Endocrine Abstracts

Background: Primary hyperparathyroidism (PHPT) and familial hypercalcaemic hypocalciuria (FHH) can both present with hypercalcaemia, but their management and prognosis are quite distinct. The 24 h urine calcium: creatinine clearance ratio (CCCR) is used to distinguish FHH from PHPT, where patients with FHH have a CCCR of <0.01. This study compares the use of a spot urine sample to measure CCCR with the gold-standard 24-h urine CCCR.

Objective: To evaluate the utility of spot urine samples for measurement of CCCR, compared against 24 h urine collection, in normocalcaemic and PTH-dependent hypercalcaemic patients.

Methods: In this dual-centre study, 18 normocalcaemic and 12 hypercalcaemic patients were identified. Spot urine samples were taken at 0900, 1400 and 2200 h, together with a 24 h collection and these were measured for calcium and creatinine. Serum adjusted calcium, creatinine and PTH were also measured and the CCCR was calculated from the 24 h collection and each of the spot urine samples.

Results: Mean serum adjusted calcium levels were 2.75 and 2.31 mmol/l for the hypercalcaemic and normocalcaemic groups with mean PTH levels of 15.53 and 4.91 pmol/l respectively. In the normocalcaemic subjects, there was statistically significant correlation between the 24 h urine collection and all spot urine samples for CCCR (P<0.0001). Bland-Altman plot showed good agreement between the two methods. In contrast, in hypercalcaemic subjects, there was no statistically significant correlation between the 24 h CCCR and each timed spot urine CCCR; nor between the 24 h CCCR and the mean CCCR of the 3 spot urine samples. Bland-Altman plot comparing 24 h and mean spot CCCR in the hypercalcaemic subjects showed poor agreement with wide limits of agreement.

Conclusion: Spot urine specimens are not clinically useful to estimate the CCCR and differentiate between PHPT and FHH. Hence, 24 h urine collection should remain the gold standard.