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

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 clinical utility 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 of FECa 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 calculating FECa can change the diagnosis of some patients whose FECa is in the gray zone.

Primer hiperparatiroidizmi olan hastalarda fraksiyone klasiyum atýlýmý hesaplanýrken albumine göre düzeltilmiþ kalsiyum mu kullanýlmalýdýr?

GÝRÝÞ ve AMAÇ: Primer hiperparatiroidizm (PHPT) ayaktan hastalarda hiperkalseminin en sýk sebebidir.Tedavi edilmediðinde progresif olarak ilerler, nefrokalsinosis ve kemik mineral kaybý geliþir ve son dönem böbrek yetmezliði, kemik kýrýklarý gibi ciddi komplikasyonlar ortaya çýkabilir. Hiperkalsemiye eþlik eden yüksek veya normal parathormonu varlýðýnda PHPT ayýrýcý tanýsýnda ailesel hipokalsiürik hiperkalsemi düþünmek gerekir. Ýki antitenin ayýrýcý tanýsýnda 24 saatlik idrarda kalsiyum atýlýmý ve fraksiyone idrar kalsiyum ekskresyonu kullanýlmaktadýr. Bu çalýþmanýn amacý fraksiyone idrar atýlýmý formülünde serum total kalsiyum düzeyini albumine göre düzeltmenin klinik anlamý olup olmadýðýný araþtýrmaktýr.
YÖNTEM ve GEREÇLER: Primer hiperparatiroidizmi olan toplam yirmi hastanýn fraksiyone idrar atýlýmý “idrarkalsiyumu x plazma kreatinin/ serum kalsiyumu x idrar kreatinin” formülü ile hesaplandý.Hesaplama yaparken serum kalsiyumu albumine göre düzeltilmiþ ve düzeltilmemiþ olarak iki ayrý ölçüm yapýldý ve ölçümler birbiriyle karþýlaþtýrýldý.
BULGULAR: Albumine göre düzeltilmiþ kalsiyum kullanýldýðýnda ortalama fraksiyone atýlýmý 0.0008(%0.8) ±0.00013, düzeltilmemiþ kalsiyum kullanýldýðýnda hesaplanan deðer ise 0.016 (%1.6) ±0.057 idi. Ýki sonuç arasýndaki fark istatistiksel olarak anlamlý idi (p=0.01). Klinik olarak PHPT ve ailesel hipokalsiürik hiperkalsemi ayýrýcý tanýsý için kesim noktasý %1 alýndýðýnda hiçbir hastada taný deðiþmezken, %2 alýndýðýnda iki PHPT’li hastanýn tanýsý ailesel hipokalsiürik hiperkalsemi olarak deðiþti
TARTIÞMA ve SONUÇ: Fraksiyone idrar atýlýmý PHPT ve ailesel hipokalsiürik hiperkalsemi ayýrýcý tanýsýnda önemlidir. Serum kalsiyum ölçümü serum albumin düzeyinden etkilenmekte ve yanlýþ yüksek veya düþük ölçülmektedir. Fraksiyone idrar atýlýmý hesaplanýrken albumine göre düzeltilmiþ kalsiyumu kullanmak, sonuçlarý gri zonda olan bazý hastalarýn klinik tanýsýný deðiþtirebilir.