Should we use corrected calcium for serum albumin when calculating the fractionated urinary calcium levels in patients with hyperparathyroidism

Abstract

INTRODUCTION:Primary hyperparathyroidism (PHPT) is the most common cause of hypercalcemia in outpatients. When left untreated, it has detrimental effects on bones and kidneys that result in fractures, nephrocalcinosis and end stage renal failure. In case of hypercalcemia if the parathyroid hormone is high or normal, there are two clinical entities to be differentiated; PHPT and familial hypocalciuric hypercalcemia (FHH). In the differential diagnosis we usually use 24 hours collection of urinary calcium and fractionated urinary calcium (FECa). In this study we aimed to determine the clinicalutility of using corrected calcium for albumin in calculation of fractionated calcium excretion in differentiating PHPT and FHH.METHODS:We conducted the study with twenty operated patients with PHPT and all had single parathyroid adenoma in the histopathology report. We retrospectively evaluated the laboratory parameters and recalculated the fractionated calcium excretion according to the corrected serum calcium for albumin. The formula for FECa is as follows; urinary calcium x plasma creatinine/ plasma calcium x urinary creatinine. Two calculations of FE Ca with and without correcting serum Ca according to serum albumin were compared with each other.RESULTS:Mean FE Ca was 0.016 ±0.057. Recalculated FE Ca excretion was 0.0008±0.0013. The difference between two calculations ofFECa was statistically different. If we accept the cutoff of FECa as 0.01 for the differentiation of PHPT from FHH, recalculation of FECa didn’t change the diagnosis in any patient. But when we accept the cut off as 0.02, two patients would have falsely been diagnosed as FHH with the new calculated FECa.DISCUSSION AND CONCLUSION:FECa is important for differential diagnosis of PHPT and FHH. Serum total calcium measurement is affected by serum albumin levels. Using corrected calcium level while calculatingFECa can change the diagnosis of some patients whose FECa is in the gray zone.