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Draft Recommendation Statement


Note: This draft Recommendation Statement is not the final recommendation of the U.S. Preventive Services Task Force. This draft is distributed solely for the purpose of pre-release review. It has not been disseminated otherwise by the USPSTF. It does not represent and should not be interpreted to represent a USPSTF determination or policy.

This draft Recommendation Statement is based on an Evidence Report that is also available for public comment. To read the accompanying draft Evidence Report on Screening for Vitamin D Deficiency and provide comments, go to http://www.uspreventiveservicestaskforce.org/draftrep.htm.

The USPSTF makes recommendations about the effectiveness of specific preventive care services for patients without related signs or symptoms.

It bases its recommendations on the evidence of both the benefits and harms of the service, and an assessment of the balance. The USPSTF does not consider the costs of providing a service in this assessment.

The USPSTF recognizes that clinical decisions involve more considerations than evidence alone. Clinicians should understand the evidence but individualize decisionmaking to the specific patient or situation. Similarly, the USPSTF notes that policy and coverage decisions involve considerations in addition to the evidence of clinical benefits and harms.

This draft Recommendation Statement is available for comment from June 24 until July 21, 2014 at 5:00 PM ET. You may wish to read the entire Recommendation Statement before you comment. A fact sheet that explains the draft recommendations in plain language is available here.


Screening for Vitamin D Deficiency: U.S. Preventive Services Task Force Recommendation Statement
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Summary of Recommendation and Evidence

The U.S. Preventive Services Task Force (USPSTF) concludes that current evidence is insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency.

This is an I statement. See the Clinical Considerations section for suggestions for practice regarding the I statement.

Table 1 describes the USPSTF grades, and Table 2 describes the USPSTF classification of levels of certainty about net benefit.

Rationale

Importance

There is no consensus definition of vitamin D deficiency, and the optimal level of total serum 25-hydroxy vitamin D (the major circulating form of vitamin D) is debated. Depending on what cutpoint is used (often <20 ng/mL or <30 ng/mL), some studies have shown that low levels of vitamin D are associated with increased risk for fractures, functional limitations, cancer, diabetes, cardiovascular disease, depression, and mortality (1).

Detection

Numerous testing methods are available to measure total serum 25-hydroxy vitamin D levels. However, the accuracy of these tests is difficult to determine due to the lack of studies using an internationally recognized reference standard and the lack of consensus on the cutpoint values used to define vitamin D deficiency. The USPSTF found evidence suggesting variation in results between testing methods and between laboratories using the same testing methods

Benefits of Detection and Early Treatment

No studies were identified that evaluated the direct benefit of screening for vitamin D deficiency in adults. Adequate evidence was found that showed treatment of asymptomatic vitamin D deficiency has no benefit on cancer, type 2 diabetes, mortality in community-dwelling adults, and risk for fractures in persons not selected based on having a high risk for fracture. The USPSTF found inadequate evidence on the benefit of treating asymptomatic vitamin D deficiency on other outcomes, including psychosocial or physical functioning. The USPSTF concluded that the overall evidence on the early treatment of asymptomatic, screen-detected vitamin D deficiency to improve overall health outcomes in adults is inadequate.

Harms of Detection and Early Treatment

No studies were identified that evaluated the direct harms of screening for vitamin D deficiency. The USPSTF found adequate evidence that the harms of treatment of vitamin D deficiency are small to none. No studies reporting on harms of treatment of vitamin D deficiency identified a significant increase in total adverse events, hypercalcemia, kidney stones, or gastrointestinal complaints.

USPSTF Assessment

The USPSTF concludes that the evidence on screening for vitamin D deficiency to improve health outcomes in asymptomatic adults is insufficient and the balance of benefits and harms of screening and early intervention cannot be determined..

Clinical Considerations

Patient Population Under Consideration

This recommendation applies to community-dwelling, nonpregnant adults age 18 years and older who are seen in primary care settings and are not known to have signs or symptoms of vitamin D deficiency or conditions for which vitamin D treatment is recommended. The focus of this statement is on screening (that is, testing for vitamin D deficiency in asymptomatic adults and treating those who are found to be deficient) and is distinct from other USPSTF statements on supplementation (that is, recommending preventive medication in patients at increased risk for a specific negative health outcome, such as falls, whether they are deficient or not).

The USPSTF recognizes that there is no consensus on how to define vitamin D deficiency and does not endorse the use of a specific threshold to identify vitamin D–deficient populations. The evidence reviewed by the USPSTF used varying cutpoint levels. For the purposes of this recommendation statement, the term “vitamin D deficiency” is used to reflect evidence found in study populations generally representing levels at 30 ng/mL or less, or the subpopulations of studies with levels less than 20 ng/mL

Suggestions for Practice Regarding the I Statement

Potential Preventable Burden

Given the lack of consensus on how to define and assess vitamin D deficiency, precise prevalence estimates of vitamin D deficiency are difficult to determine. In order to collect precise estimates, accurate assay methods, an internationally recognized reference standard, and a cutpoint for defining vitamin D deficiency need to be established. Reported estimates of the prevalence of vitamin D deficiency vary widely depending on the time period, cutpoint, study population, study design, and testing method used; reported estimates range from as low as 19% using a statistical modeling approach (2) to as high as 77% based on National Health and Nutrition Examination Survey (NHANES) data from 2001 to 2004 using a cutpoint value of less than 30 ng/mL (3).

It is difficult to evaluate the effect of vitamin D levels on health outcomes. Lower vitamin D levels have been reported to increase risk for fractures, falls, functional limitations, some cancers, diabetes, cardiovascular disease, depression, and mortality. However, observations of these associations have been inconsistent and may vary depending on the cutpoint used to define low vitamin D levels and by subpopulations (defined by race and institutionalized populations). For example, African Americans have paradoxically lower reported rates of fractures despite having increased prevalence of low vitamin D levels compared with whites.

If a threshold total serum 25-hydroxy vitamin D value could be established to define vitamin D deficiency and if testing assays could be standardized, the goal of screening for vitamin D deficiency would be to identify and treat vitamin D deficiency before the occurrence of associated adverse clinical outcomes. However, current evidence is inadequate to support the recommendation that screening and treatment of asymptomatic low 25-hydroxy vitamin D levels improves clinical outcomes in community-dwelling adults.

Potential harms

Screening could cause misclassification of vitamin D–deficient persons because of the uncertainty of the cutpoint for defining vitamin D deficiency and the variability of available assays. This could result in overdiagnosis (which could lead to nondeficient persons receiving unnecessary treatment) or underdiagnosis (which could lead to deficient persons not receiving treatment).

A rare potential harm of oral vitamin D treatment is toxicity, which may lead to hypercalcemia, hyperphosphatemia, suppressed parathyroid hormone, and hypercalciuria. However, the level associated with 25-hydroxy vitamin D toxicity (often defined as >200 ng/mL) (4) is well above the level considered to be sufficient. Vitamin D with calcium may also be associated with increased risk for kidney stones; vitamin D alone does not appear to increase risk for kidney stones. In general, oral vitamin D treatment does not appear to be associated with serious harms. Harms of treating vitamin D deficiency with increased sun exposure (specifically ultraviolet B [UVB] radiation) include increased risk for skin cancer. Because of this concern, increased sun exposure is not generally recommended as a treatment for vitamin D deficiency.

Cost

Numerous vitamin D level testing methods are available and the cost of screening varies.

Current practice

Testing rates for vitamin D levels appear to be increasing despite the uncertainties about the definition of vitamin D deficiency. Although estimates on vitamin D deficiency screening rates in primary care settings are not available, a recent study evaluating 2007 to 2010 data from the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey found that the annual rate of visits associated with a diagnosis code for vitamin D deficiency more than tripled between 2008 to 2010 (with 1,177 visits per 100,000 population in 2010) (5). Additionally, according to a 2009 survey, total serum 25-hyrdroxy vitamin D testing increased by at least 50% compared with the previous year in over half of the clinical laboratories surveyed (6).

Assessment of Risk

Although there is not enough evidence to support screening for vitamin D deficiency, there is some evidence on what factors may increase an individual's risk for vitamin D deficiency. Persons with low vitamin D intake, decreased vitamin D absorption, and little or no sun exposure (such as due to the winter season, high latitude, and physical sun avoidance) may be at increased risk for vitamin D deficiency (1). Obesity and darker skin pigmentation may also be associated with low levels of total serum 25-hydroxy vitamin D, but it is unclear whether these factors reflect vitamin D deficiency and increase risk for adverse clinical outcomes. Obesity may allow for greater sequestration of vitamin D into adipose tissue, however, this vitamin D may still be bioavailable (1). Increased skin pigmentation reduces the skin's ability to produce vitamin D in response to UVB exposure. Prevalence rates of low total serum 25-hydroxy vitamin D are 2 to 9 times higher in African Americans and 2 to 3 times higher in Hispanics compared with whites (1), yet risk for fracture in African Americans is half of that in whites (7). Although other factors such as body composition and calcium economy have been proposed to explain this paradox (8), a recent study suggests that although total serum 25-hydroxy vitamin D levels in African Americans may be low, the concentration of bioavailable 25-hydroxy vitamin D levels may not be low (1, 9). Some evidence suggests that older age and female sex may also be associated with increased risk for vitamin D deficiency, however, these findings are inconsistent (1).

Screening Tests

Current vitamin D assays measure total serum 25-hydroxy vitamin D levels to determine vitamin D status (that is, whether a person is considered deficient or nondeficient). Numerous testing methods are available, including competitive protein binding, immunoassay, high pressure liquid chromatography (HPLC), and combined HPLC and mass spectrometry (LC-MS/MS). However, the sensitivity and specificity of these tests are unknown due to the lack of studies using an internationally recognized reference standard. Variability between assay methods and between laboratories using the same methods may vary by 10% to 20%, and classification of samples as “deficient” or “nondeficient” may vary by 4% to 32% depending on which assay is used (1).

Treatment or Interventions

Most often, oral vitamin D is used to treat vitamin D deficiency (other treatment options include increasing dietary vitamin D intake or UVB exposure). Commonly available forms of oral vitamin D include vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).

Additional Approaches to Prevention

According to the Institute of Medicine (IOM), daily dietary vitamin D intake of 600 IU in adults ages 18 to 70 years and 800 IU in adults older than 70 years should be sufficient to meet the needs of 97.5% of the adult population (10). UVB exposure can also increase vitamin D levels, however, numerous variables (such as time of day, season, cloud cover, skin pigmentation, and sunscreen use) can affect how long of an exposure is needed to attain sufficient vitamin D levels. Sun exposure to prevent vitamin D deficiency is not generally recommended because it increases the risk for skin cancer associated with UVB radiation.

Useful Resources

The USPSTF has published statements on the use of vitamin D supplementation for prevention of falls and fractures and statements on the use of vitamins for the prevention of cardiovascular disease or cancer (available at www.uspreventiveservicestaskforce.org). These other statements differ from the current statement in that they address vitamin D supplementation in certain populations at high risk for falls, fractures, cardiovascular disease, or cancer, without first determining a patient's vitamin D status.

Other Considerations

Research Needs and Gaps

The lack of an accurate screening strategy to identify vitamin D deficiency, especially in important subpopulations (such as African Americans), is a critical gap in the evidence. Further research is needed to determine: a cutpoint level to define vitamin D deficiency, testing sensitivity and specificity of the various assays using an internationally accepted reference standard, and if total serum 25-hydroxy vitamin D is the best measure of vitamin D deficiency in all populations. Further studies are also needed to evaluate which treatment regimens may benefit specific vitamin D–deficient populations. In particular, studies on treatment of vitamin D deficiency in males and in non-Caucasian ethnic groups were absent from the evidence base. Lastly, further studies are needed to evaluate the harms of screening for and treatment of vitamin D deficiency.

Discussion

Burden of Disease

Vitamin D is a fat-soluble vitamin that helps regulate calcium homeostasis and bone health. Important sources of vitamin D include diet (such as fatty fish, cod liver oil, dairy products, fortified beverages and foods, and supplements) and endogenous synthesis triggered by UVB exposure. Inadequate dietary vitamin D intake, decreased vitamin D absorption, and limited UVB exposure can all lower vitamin D levels, but the exact threshold to define vitamin D deficiency is not well established. Furthermore, the association between vitamin D status and health outcomes is unclear.

Severe and prolonged vitamin D deficiency can cause bone mineralization diseases, such as rickets in children and osteomalacia in adults. Other health effects caused by more moderate decreases in vitamin D levels remain difficult to determine and were the focus of the current review. Studies have evaluated the association between vitamin D status and health outcomes such as fractures, falls, cancer, cardiovascular disease, mortality, functional limitations, diabetes, and depression. Results have varied depending on the cutpoint level used to define deficiency, population, and setting (1). Overall, studies tend to suggest decreased risk for colorectal cancer with higher 25-hydroxy vitamin D levels and either an inverse or U-shaped relationship with mortality. Studies on fractures, falls, and cardiovascular disease risk have been more inconsistent; increased fracture and cardiovascular disease risk were found most often in white populations and increased risk for falls were found most often in institutionalized populations. Few studies have evaluated associations with functional limitations, diabetes, and depression, but these studies generally suggest an increased risk with lower 25-hydroxy vitamin D levels (1).

Childhood rickets has become relatively rare in the United States since vitamin D–fortified milk was introduced in the 1930s. Prevalence rates of less clinically overt vitamin D deficiency are much more difficult to characterize given the uncertainty about how to define adequate levels of vitamin D and what cutpoint to use to define vitamin D deficiency. Additionally, the lack of a vitamin D testing reference standard until recently has further complicated accurate measurement of vitamin D deficiency prevalence rates.

A recent study using a statistical probability approach estimated that 19% of the U.S. population is at risk for vitamin D inadequacy (2). Based on NHANES data, 33% of the U.S. population had 25-hydroxy vitamin D levels at 20 ng/mL or less from 2001 to 2006 (11) and 77% had 25-hydroxy vitamin D levels less than 30 ng/mL from 2001 to 2004 (3).

Commonly reported risk factors for low 25-hydroxy vitamin D levels are decreased dietary vitamin D intake, absorption, or synthesis due to decreased sun exposure or darker skin pigmentation; older adults; persons with inflammatory bowel disease, malabsorptive conditions, or history of gastric bypass; persons who are homebound or institutionalized; persons who routinely wear clothing that prevents sun exposure on most of their skin; or persons living at high latitudes (12).

Populations with darker skin pigmentation, such as African Americans, Hispanics, and Asians, have also been found to have lower 25-hydroxy vitamin D levels compared with white populations. According to the Second National Report on Biochemcial Indicators of Diet and Nutrition in the U.S. Population (based on NHANES data from 2003 to 2006) 21.7% of whites had 25-hydroxy vitamin D levels of 20 ng/mL or less compared with 70.6% of African Americans and 44.2% of Hispanics, and the geometric mean of 25-hydroxy vitamin D levels in adults age 20 years and older ranged from 23.0 to 25.6 ng/mL in whites compared with 13.0 to 14.5 ng/mL in African Americans and 17.8 to 18.6 ng/mL in Hispanics. However, it is unclear if low 25-hydroxy vitamin D levels in these populations are associated with adverse clinical outcomes. For example, the increased risk for fractures and cardiovascular disease with low 25-hydroxy vitamin D levels observed in some studies of whites has not been found in African Americans (1). A recent study suggests that although total serum 25-hydroxy vitamin D levels may be lower in African Americans compared with whites, bioavailable 25-hydroxy vitamin D concentrations may be similar between the two populations when vitamin D binding protein is considered (9). If substantiated with further research, this finding could potentially explain why higher rates of low total serum 25-hydroxy vitamin D levels without an associated higher risk for fracture have been reported in African Americans and would put into question the use of total serum 25-hydroxy vitamin D measurements to identify vitamin D deficiency in all populations.

Obese populations have also been found to have increased rates of low 25-hydroxy vitamin D levels, however, this may be due to either increased vitamin D requirements or greater sequestration of vitamin D into adipose tissue. It is unclear if low 25-hydroxy vitamin D levels in obese persons are associated with negative clinical outcomes (1, 10, 12).

Scope of Review

This is a new topic for the USPSTF. Evidence on screening for vitamin D deficiency, including benefits and harms of screening and early treatment, was reviewed. The scope of the review focused on community-dwelling, nonpregnant adults age 18 years and older who did not have clinical signs of vitamin D deficiency and were seen in primary care settings. Only oral vitamin D formulations were reviewed; treatment with nonoral vitamin D therapies or UVB exposure was excluded.

Accuracy of Screening Tests

Despite the availability of numerous testing methods to measure total serum 25-hydroxy vitamin D levels, the sensitivity and specificity of these tests is currently unknown given the lack of studies using an internationally recognized, commutable reference standard. Testing variability between methods and between laboratories using the same method has been observed, and whether a patient's sample is classified as “deficient” or “nondeficient” has been found to vary by 4% to 32% depending on which assay is used (1). Recently, programs have been initiated to improve testing accuracy and establish standardization of measurements. The National Institute of Standards and Technology (NIST) developed a standard reference material for 25-hydroxy vitamin D in 2009 that appears to improve testing accuracy of LC-MS/MS methods, but has limited impact on improving accuracy of immunoassay methods. Since 2010, the Vitamin D Standardization Program has sought to standardize the laboratory measurement of vitamin D status through international collaboration* and coordination of efforts, and it has developed protocols for standardizing procedures for measuring total serum 25-hydroxy vitamin D for NHANES. However, these protocols are not yet available for commercial or other research laboratory use. Several external accuracy-based testing systems are available for commercial and research laboratory use, such as the Vitamin D Metabolites Quality Assurance Program (established by NIST and the National Institutes of Health) and the Vitamin D External Quality Assurance Scheme (1).

In addition to the uncertainty regarding the accuracy of tests measuring total serum 25-hydroxy vitamin D levels, it is unclear if total serum 25-hydroxy vitamin D is the best indicator of vitamin D status or if bioavailable 25-hydroxy vitamin D should be used instead. As noted above, a 2013 study found that although African American study participants had lower total serum 25-hydroxy vitamin D levels compared with white study participants, both groups had similar concentrations of bioavailable 25-hydroxy vitamin D. This study highlights the difficulty of using a universal total serum 25-hydroxy vitamin D cutpoint to define deficiency across different races. However, more research is needed before this can be concluded and commercial testing of bioavailable 25-hydroxy vitamin D levels is not currently available.

Effectiveness of Early Detection and Treatment

Overall, the USPSTF reviewed 16 trials and 1 nested case control study that evaluated the effects of treatment of vitamin D deficiency on health outcomes in populations not selected based on signs or symptoms of vitamin D deficiency (1). Generally, the studies included older adults (the majority of studies had a mean study age greater than 65 years) that were predominantly female (12 of the studies included female participants only) and community dwelling, although four studies were conducted in exclusively institutionalized settings. All studies were conducted in the United States or Europe, with the majority of studies conducted exclusively in Europe. The studies used vitamin D3 doses of 400 to 4,800 IU daily or 8,400 to 50,000 IU weekly, and five of the studies included treatment with calcium. Followup in the studies ranged from 2 months to 7 years.

No studies directly assessed the effectiveness of screening for vitamin D deficiency. Seventeen studies were evaluated by the USPSTF that assessed the effectiveness of oral vitamin D treatment on various health outcomes (such as mortality, falls, fractures, cancer, diabetes, and physical and psychosocial functioning) in vitamin D–deficient participants not selected based on signs or symptoms of vitamin D deficiency (1). Three studies conducted in Europe reported results suggesting a benefit in mortality in older,institutionalized patients treated for vitamin D deficiency. However, no benefit in mortality was seen after meta-analysis was performed on the eight studies limited to community-dwelling populations (1). Studies on vitamin D treatment and falls reported mixed results. Five studies evaluated the effect of treating vitamin D deficiency on the risk for fracture, and no studies individually or when aggregated in meta-analysis found a benefit in treating vitamin D deficiency to decrease fracture risk (1). Few studies evaluated the effect of treating vitamin D deficiency on risk for cancer or diabetes or on physical or psychosocial functioning, but generally no association was seen (1).

Potential Harms of Early Detection and Treatment

No studies directly assessed the harms of screening for vitamin D deficiency. Twenty-three studies (1) were identified that reported on adverse effects of vitamin D treatment, however, most trials were not designed to assess harms, and reporting of adverse events was generally suboptimal. Study participants were predominantly female, although two studies were exclusively male. The mean age of study participants ranged from 31 to 85 years and the majority of studies were conducted in Europe. Five studies were conducted exclusively in institutionalized settings. Doses of vitamin D used in the studies that reported harms ranged from 400 to 7,000 IU per day and 8,400 to 54,000 IU per week, and five studies included treatment of vitamin D and calcium. Followup in the studies ranged from 6 weeks to 4 years.

No significant difference in rates of serious adverse events or rates of withdrawals due to adverse events was reported by any individual study or found in aggregate meta-analysis (1). Seventeen trials evaluated the risk for hypercalcemia with vitamin D treatment. No individual study reported a significantly higher incidence of hypercalcemia, and overall, 1.7% of treated participants compared with 1.3% of control participants were found to have hypercalcemia in trials that reported at least one case of hypercalcemia. However, the overall cases of hypercalcemia were low and seven trials reported no cases. Seven trials reported on risk for kidney stones, two of which included treatment with vitamin D and calcium, however, no kidney stones were reported in any participants.

Estimate of Magnitude of Net Benefit

Overall, the USPSTF concludes that the current evidence is insufficient to determine the net balance of benefits and harms of screening and early treatment of vitamin D deficiency in community-dwelling, U.S. primary care adult populations. No studies were identified that evaluated the treatment of screen-detected vitamin D deficiency. Studies varied in testing methods, cutpoint used to define vitamin D deficiency, and treatment regimens. Furthermore, most studies were conducted in elderly white (mostly European) and predominantly female populations, and thus application of the evidence to the general U.S. primary care population is difficult.

The USPSTF found evidence suggesting significant variation in the way vitamin D is measured and great uncertainty about the specific vitamin D level that should be used to determine when treatment with vitamin D would improve health. Furthermore, information is lacking on how to measure and treat vitamin D deficiency in specific subpopulations, such as men, non-White ethnic groups, and less elderly populations. Based on the current, available science, the USPSTF concludes that the evidence on screening for vitamin D deficiency to improve health outcomes is insufficient and the balance of benefits and harms of screening and early intervention cannot be determined.

Recommendations of Others

No national, primary care professional organization currently recommends populationwide screening for vitamin D deficiency. The Endocrine Society recommends screening for vitamin D deficiency only in persons at risk, and states that there is no evidence showing benefits of screening at a population level (13). The Endocrine Society defines vitamin D deficiency using total serum 25-hydroxy vitamin D levels less than 20 ng/mL and vitamin D insufficiency as total serum 25-hydroxy vitamin D levels from 21 ng/mL to 29 ng/mL; treatment is recommended for vitamin D–deficient persons. Further information on the Endocrine Society's clinical practice guideline can be found at www.endocrine.org.

Other organizations, including the American College of Obstetricians and Gynecologists (14), the American Geriatric Society (www.ags.org), and the National Osteoporosis Foundation (15), have recommendations on testing for vitamin D as a part of osteoporosis management.

The IOM has no formal guideline on vitamin D deficiency screening, but it has published a report on the recommended dietary allowance (RDA) for vitamin D (10). The RDA is the estimated requirement to meet or exceed the vitamin D needs for 97.5% of the population. Assuming minimal sun exposure, the IOM's RDA is 600 IU per day for adults ages 19 to 70 years and 800 IU per day for adults older than age 70 years. Furthermore, the IOM concluded that total serum 25-hydroxy vitamin D levels of 16 ng/mL meet the needs of approximately half of the population, and levels of 20 ng/mL or greater meet the needs for nearly all the population.

Table 1: What the Grades Mean and Suggestions for Practice

Grade Definition Suggestions for Practice
A The USPSTF recommends the service. There is high certainty that the net benefit is substantial. Offer or provide this service.
B The USPSTF recommends the service. There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial. Offer or provide this service.
C The USPSTF recommends selectively offering or providing this service to individual patients based on professional judgment and patient preferences. There is at least moderate certainty that the net benefit is small. Offer or provide this service for selected patients depending on individual circumstances.
D The USPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits. Discourage the use of this service.
I Statement The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined. Read the clinical considerations section of USPSTF Recommendation Statement. If the service is offered, patients should understand the uncertainty about the balance of benefits and harms.


Table 2: Levels of Certainty Regarding Net Benefit

Level of Certainty* Description
High The available evidence usually includes consistent results from well-designed, well-conducted studies in representative primary care populations. These studies assess the effects of the preventive service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies.
Moderate The available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by factors such as:
  • The number, size, or quality of individual studies.
  • Inconsistency of findings across individual studies.
  • Limited generalizability of findings to routine primary care practice.
  • Lack of coherence in the chain of evidence.

As more information becomes available, the magnitude or direction of the observed effect could change, and this change may be large enough to alter the conclusion.

Low The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of:
  • The limited number or size of studies.
  • Important flaws in study design or methods.
  • Inconsistency of findings across individual studies.
  • Gaps in the chain of evidence.
  • Findings not generalizable to routine primary care practice.
  • A lack of information on important health outcomes.

More information may allow an estimation of effects on health outcomes.

*The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.

References

1. LeBlanc E CR, Zakhler B, Fraenkel M, Pappas M. Screening for Vitamin D Deficiency: Systematic Review for the U.S. Preventive Services Task Force Recommendation. Evidence Synthesis No. 118. AHRQ Publication No. 13-05183-EF-1. Rockville, MD: Agency for Healthcare Research and Quality; 2014.
2. Taylor CL, Carriquiry AL, Bailey RL, Sempos CT, Yetley EA. Appropriateness of the probability approach with a nutrient status biomarker to assess population inadequacy: a study using vitamin D. Am J Clin Nutr. 2013;97(1):72-8.
3. Ginde AA, Liu MC, Camargo CA, Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009;169(6):626-3.
4. Jones G. Pharmacokinetics of vitamin D toxicity. Am J Clin Nutr. 2008;88(2):582S-586S.
5. Huang KE MB, Davis SA, Feldman SR. Surge in US outpatient vitamin D deficiency diagnoses: National Ambulatory Medical Care Survey analysis. South Med J. 2014;107(4):214-7.
6. Rollins G. Vitamin D testing—What's the right answer? Labs grapple with confusing analytics, evidence. Clin Lab News. 2009;35(7):1, 6, 8.
7. Barrett-Connor E, Siris ES, Wehren LE, Miller PD, Abbott TA, Berger ML, et al. Osteoporosis and fracture risk in women of different ethnic groups. J Bone Miner Res. 2005;20(2):185-94.
8. Aloia JF. African Americans, 25-hydroxyvitamin D, and osteoporosis: a paradox. Am J Clin Nutr. 2008;88(2):545S-550S.
9. Powe CE, Evans MK, Wenger J, Zonderman AB, Berg AH, Nalls M, et al. Vitamin D-binding protein and vitamin D status of black Americans and white Americans. N Engl J Med. 2013;369(21):1991-2000.
10. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press; 2011.
11. Looker AC, Johnson CL, Lacher DA, Pfeiffer CM, Schleicher RL, Sempos CT. Vitamin D status: United States, 2001-2006. NCHS Data Brief. 2011;(59):1-8.
12. National Institutes of Health. Vitamin D: fact Sheet for health professionals. Bethesda, MD: Office of Dietary Supplements, National Institutes of Health; last updated June 24, 2011. Accessed at http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h5 on 25 April 2014.
13. Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-30.
14. Committee on Practice Bulletins-Gynecology; The American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 129. Osteoporis. Obstet Gynecol. 2012;120:718-34
15. National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2014.

* National Institutes of Health Office of Dietary Supplements; the National Institute for Standards and Technology; the Centers for Disease Control and Prevention; the Vitamin D External Quality Assessment Scheme; the College of American Pathologists; the American Association for Clinical Chemistry; the International Federation of Clinical Chemistry and Laboratory Medicine; the Laboratory for Analytical Chemistry; and the Faculty of Pharmaceutical Sciences, Ghent University.

AHRQ Publication No. 13-05183-EF-2
Current as of June 2014


Internet Citation:

U.S. Preventive Services Task Force. Screening for Vitamin D Deficiency: Draft Recommendation Statement. AHRQ Publication No. 13-05183-EF-2. http://www.uspreventiveservicestaskforce.org/draftrec.htm



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