Vitamin D assessment in primary care: changing patterns of testing

Over recent years there has been increased interest in the disease burden associated with vitamin D deficiency. This, combined with recognition that the prevalence of vitamin D deficiency is high in the UK, has led to increased requests for vitamin D assessment from primary care clinicians.

A primary care cohort in Liverpool.

How has the usefulness of vitamin D testing changed over time in identifying deficiency?

Vitamin D results from primary care practices in Liverpool were collected between 2007 and 2012, inclusive. Results were allocated to six cohorts based on year of request and each was grouped into three categories (adequate, insufficient and deficient).

Vitamin D results of 9460 (74%) first tests and 3263 (26%) retests were analysed. Total number of requests increased 11-fold, from 503 in 2007 to 5552 in 2012. Overall 42% of first-test results were deficient (< 30 nmol). With each incremental year, more cases of vitamin D deficiency were detected - but the odds of detecting vitamin D deficiency decreased.

An exponential increase in the number of vitamin D requests was observed over this six-year period. Although more patients with vitamin deficiency were identified, the increased number of tests represents a significant cost to health services. Moreover, the practice of retesting too soon after treatment can be inappropriate. There is a need to develop clear guidance for assessing vitamin D status in primary care.