Background There is increasing awareness of the importance of vitamin D for maintaining musculoskeletal health by both the medical profession and the public. Vitamin D appears to have effects on both innate and acquired immunity and deficiency may be associated with both susceptibility and disease severity in rheumatological conditions.1 Consequently rates of testing for vitamin D deficiency are increasing, particularly in primary care. These expensive tests can place substantial financial burdens on health services, particularly if testing is performed indiscriminately.
Objectives The aim of this study was to identify trends in measurement of vitamin D (25OHD) in primary care over time and to explore the utility of testing.
Methods This observational study used fully anonymised 25OHD results, from 2007 to 2012 inclusive, obtained from primary care practices in Liverpool, UK. The definition of deficiency (25OHD<30mol/L), insufficiency (30-50nmol/L) and adequacy (>50nmol/L) were as defined by recent National Osteoporosis Society (NOS) and Institute of Medicine (IOM) guidelines.2
Results In the six-year period a total of 12,772 samples were sent from primary care practices across Liverpool. The number of tests rose from 503 in 2007 to 5,552 in 2012. The median age of requests for the whole cohort was 50 years. Females were tested more frequently than males for each age category with the gender difference most marked during reproductive years. Over the six year period 40% of results from initial requests demonstrated vitamin D deficiency, 26% were insufficient and 34% were adequate. Adjusted for age and sex, the odds of finding a deficient result was 2.46 times higher (95% CI 1.93, 3.13) in 2007 compared to 2012. The proportion of vitamin D deficiency each month followed a sinusoidal pattern (figure 1). Deficiency was detected at higher proportions in winter (December to February) than summer (June to August) (50% vs 29% respectively, P=0.003). Median vitamin D levels were 31nmol/L in winter (IQR 17.6 to 51.7nmol/L) compared to 46.3nmol/L in summer (IQR 27.5-67.3nmol/L) (P<0.001).
Conclusions This study has demonstrated a marked rise in frequency of requests for vitamin D measurement in primary care over a recent six-year period. Primary care practices in Liverpool ordered over £100,000 worth of vitamin D tests in 2012, eleven times the amount in 2007. Although the absolute number of deficient individuals identified had increased each year, the odds of finding a deficient result became lower. Winter levels of vitamin D may not reflect the year-round vitamin D status of individuals and it may not be necessary to treat those identified as borderline deficient in winter. Conversely a person with a borderline insufficient result in autumn is likely to become deficient over the winter. Clinicians should think carefully before testing patients for vitamin D deficiency and consider whether supplementation would be an alternative.
Kulie T, Groff A, Redmer J, et al. Vitamin D: an evidence-based review. J Am Board Fam Med. 2009 Nov-Dec;22(6):698-706.
Vitamin D and Bone Health: A Practical Clinical Guidelines for Patient Management. National Osteoporosis Society. 2013.
Disclosure of Interest None declared
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