Vitamin D retesting by general practitioners: a factor and cost analysis.

Abstract

Vitamin D testing by Primary Care doctors is increasing, placing greater workloads on healthcare systems. There is little data though on vitamin D retesting in Ireland. This study aims to investigate the factors associated with vitamin D retesting by Irish General Practitioners (GPs) and examine the resulting costs. This is a retrospective analysis over 5years (2014-2018) of GP requested 25-hydroxyvitamin D (25(OH)D) results in 36,458 patients at a major city hospital in Dublin, Ireland. Those with one test were compared with individuals who were retested and samples categorised to determine changes in status between tests. Nearly one in four patients (n=8,305) were retested. Positive predictors of retesting were female (p<0.001), age (60-69years, p<0.001), location (Co. Kildare, p<0.001) and initial deficiency (<30nmol/L, p<0.001) or insufficiency (30-49.9nmol/L, p<0.001). Vitamin D status improved on retesting, with deficiency halving on first retest (9 vs. 18%, p<0.001) and dropping to 6% on further retests. About 12.2% of retests were done within 3months and 29% had≥2 retests within 1year. 57% of retests were in those initially vitamin D replete (>50nmol/L). The annual cost of inappropriate testing was €61,976. One in four patients were retested and this varied by age, gender and patient location. Over 10% of retests were inappropriately early (<3months), a third too frequent and over half were in replete individuals incurring significant costs. Clear guidance for GPs on minimum retesting intervals is needed, as well as laboratory ordering systems to limit requests using pre-defined criteria.