Background: Prevalence of FHH in hypercalcaemic patients with a raised PTH has been quoted as 1 in 20. Parathyroidectomy has no benefit and therefore it is important to exclude FHH prior to considering surgery.
Objectives: The aim of our study was to idenitify hypercalcaemic patients with a 24 hour urine calcium creatinine ratio (Ca/Cr) between 0.010.02 with a view to propose a cut-off ratio of 0.015 which will provide optimal discrimination between FHH and PHPT.
Study: We conducted a retrospective analysis of hypercalcaemic patients in a large tertiary centre, recording clinical and biochemical data, CaSR gene results, radiology and post-operative histology. The study group included 88 patients with hypercalcaemia with a mean age of 59 yrs (F:M ratio=3:1). Most patients had sporadic PHPT (n=58 (65%) confirmed by histology and post-op calcium. 24 hour urine Ca/Cr ratio was found to be <0.015 in 38 (43%) patients. In this group, 5 patients were CaSR gene mutation positive FHH and 17 patients (68%) had probable diagnosis of FHH with positive family history and/or no end organ damage. 2 patients who tested positive for CaSR gene mutation had a Ca/Cr of 0.014 even with normal vitamin D levels.
50 (56%) patients had a ratio >0.015, 90% of whom had a confirmed diagnosis of PHPT either by concordant imaging (USS and MIBI) or by parathyroid surgery. The remaining 10% of patients had a clinical diagnosis of PHPT as they were symptomatic and/or had end organ damage but were on conservative management. None of these patients were tested positive for CaSR gene or had clinical suspicion for FHH.
Conclusion: The major feature that distinguishes FHH from PHPT is a low 24 hour urine Ca/Cr ratio. In our study, we have shown that a Ca/Cr clearance ratio <0.015 has 100% sensitivity for FHH, 75% specificity and a negative predictive value of 100%. Based on this study, FHH should be strongly considered in all vitamin D replete patients with a 24 hour urine Ca/Cr ratio of <0.015.