With increasing recognition of more subtle presentations of primary hyperparathyroidism (pHPT), laboratory values are frequently seen in a range that would be expected for patients who have familial hypercalcemic hypocalciuria (FHH). Calcium creatinine clearance ratio (CCCR) has been advocated as a diagnostic tool to differentiate between these two disorders. However, it is limited by an indeterminate range (0.01-0.02). The aim of this study is to assess the relevance of CCCR in a modern series of patients with surgically managed pHPT.

We performed a retrospective cohort study of 1000 patients who underwent parathyroid surgery for pHPT over eleven years. CCCR was evaluated by degree of biochemical derangement, single versus multiple gland disease and interfering medications.

Patient demographics and resected histopathology were typical for a current series of patients with pHPT. In retrospect, none of the patients were suspected to have FHH post operatively. CCCR was less than 0.01 for 19.0%, between 0.01-0.02 for 43.7% and greater than 0.02 in 37.3%. Distribution of CCCR for patients free from interfering medications and different histological subtypes were the same. One third of the cohort had mild calcium elevations, more typical for FHH. Of these, almost two thirds had a CCCR in a range suspect for FHH (<0.02).

To our knowledge this is the largest series to evaluate the validity of CCCR for patients with surgically confirmed pPHT. The utility of CCCR in screening for FHH is limited, as 63% of modern patients with confirmed pHPT have low values.