Requesting patterns for serum calcium concentration in patients on long-term lithium therapy

Long-term lithium therapy is associated with hypercalcaemia in 10-60% of patients, but unlike creatinine and thyroid stimulating hormone (TSH), monitoring by general practitioners of serum calcium for patients on lithium is not a requirement of the Qualities and Outcomes Framework (QOF) of 2004. We aimed to assess requesting patterns for serum calcium in patients on long-term lithium therapy and subsequent diagnosis of hypercalcaemia.

We identified 100 patients on long-term lithium therapy, as indicated by regular monitoring of lithium levels in our laboratory for at least 1 year. We determined how many of these patients had had serum calcium analysed, noting the assay date, concentration, source of request and clinical details stated.

Forty-three out of hundred patients had serum calcium analysed during the course of their treatment including 28 in the previous 15 months. Twenty-one patients had serum calcium analysed by their GP, including 12 in the previous 15 months. Hypercalcaemia was diagnosed in five patients (11.6%).

A significant proportion of patients in whom calcium was checked developed hypercalcaemia on lithium therapy. However, only 12% of the patients had serum calcium requested by their GP in the previous 15 months, which compares unfavourably with TSH and creatinine, for which monitoring approaches 100%. We recommend that serum calcium be checked every 15 months along with creatinine and TSH. This might be achieved by incorporating appropriate targets into the QOF, or by reflective or reflex adding-on of calcium to lithium specimens from patients who have not had calcium analysed in the previous 15 months.