Sociodemographic correlates of 25-hydroxyvitamin D test utilization in Calgary, Alberta

Increasing laboratory test utilization is a major challenge facing clinical laboratories. However, in most instances we lack population level information on the patient groups to which increased testing is directed. Much recent work has been published on the sociodemographic correlates of 25-hydroxyvitamin D deficiency. An unanswered question, however, is whether testing is preferentially directed towards individuals with a higher likelihood of deficiency. In this paper we examine this question by combining laboratory information system data on testing rates with Census Canada data.

We examined 1,436 census dissemination areas within the city of Calgary, Alberta, Canada. For each census dissemination area we determined age and sex-specific 25-hydroxyvitamin D testing rates over a one year period. We then compared these testing rates with the following sociodemographic variables obtained from Census Canada: first nations status, education level, household income, visible minority status, and recent immigrant status.

Overall, 6.9% of males in the city of Calgary were tested during the study period. Females were 1.7 times more likely to be tested than males. Testing rate increased with increasing age, with 16.8% of individuals 66 years and over tested during the one-year study period. Individuals having at least some university education were less likely to be tested (RR = 0.60; p < 0.0001). Interestingly, although visible minorities were over twice as likely to be tested as compared to non-visual minorities (RR = 2.25; p < 0.0001), recent immigrants, a group known to exhibit low 25 hydroxyvitamin D levels, were significantly less likely to be tested than non-recent immigrants (RR = 0.72; p = 0.0174). While median household income was modestly associated with increased testing (RR = 1.02; p < 0.0001), First Nations status and non-English speaking were not significant predictors of 25-hydroxyvitamin D testing.

Testing for 25-hydroxyvitamin D is in part directed toward populations at higher risk of deficiency (visible minorities) and at higher risk of osteoporosis (older females), but a particularly high risk group (recent immigrants) is being tested at a lower rate than other patient groups.