Calcium requests in a primary care; An observational audit of biochemical requests and frequency of abnormal results

This aim of this audit was to assess the extent of serum calcium testing and the frequency of hypercalcaemia in the primary care setting. We also assessed the appropriateness of subsequent investigations with repeat serum calcium and PTH testing if hypercalcaemia was identified.

All laboratory requests for adjusted calcium and PTH samples sent from primary care in Glasgow were analysed over a 12 month period. This covered approximately 125 GP practices and a patient population of over 590,000.

There were 78,845 requests for adjusted calcium and 2053 PTH requests from 62,745 patients aged 16-105 years (median age 57, IQ range 30 years). Of these requests 1423 (2.3%) of patients had biochemical evidence of hypercalcaemia (adjusted calcium ≥ 2.61 mmol/L). Of the 1423 patients with hypercalcaemia, 368 patients (45.8%) had a single raised calcium level that was within the normal range on repeat testing. Of the 400 patients with persistent hypercalcaemia on 2 or more samples, 210 (52.5%) had a PTH measured. Eight patients had a PTH < 2.0 pmol/L, whilst 202 (96.1%) had a PTH ≥ 2.0 pmol/L (range 2.1-106.1 pmol/L).

Serum calcium was checked in 10.6% of the population per year within primary care. In the 2.4% with a raised calcium on initial testing, approximately half (45.8%) will normalise on repeat testing. Of those who remained persistently hypercalcaemic, only half (52.5%) had a PTH measured and the majority (96.1%) were in keeping with primary hyperparathyroidism being the most common cause of hypercalcaemia.