Introduction: The aim of this study was to assess calcium-phosphate metabolism of autosomal dominant polycystic kidney disease (ADPKD) patients with a special consideration to the following serum parameters: calcium (Ca²⁺), inorganic phosphate (Pi), parathyroid hormone (PTH) and intracellular erythrocyte calcium ([Ca²⁺]i) concentrations.
Material and methods: The study included 49 adult ADPKD patients (19 males, 30 females) aged 36 ±11 years with normal renal function and no diagnosis of diabetes as well as 50 healthy controls (22 males, 28 females) matched for age and gender. Serum concentrations of sodium (Na+), potassium (K+) and magnesium (Mg2+) ions and Pi were determined with an indirect ion-selective method, while Ca²⁺ concentration was measured with a direct ion-selective method. The PTH was detected using a radioimmunometric method. [Ca²⁺]i concentration was determined with the Ca²⁺ sensitive fluorescent dye Fura-2 method.
Results: In the ADPKD group, when compared to controls, the following concentrations were significantly higher: serum Ca²⁺ (1.18 ±0.06 mmol/l vs. 1.15 ±0.06 mmol/l, p = 0.0085), [Ca²⁺]i (146.9 ±110.0 nmol/l vs. 96.5 ±52.7 nmol/l, p = 0.0075), serum Na+ (139.4 ±2.7 mmol/l vs. 138.5 ±2.1 mmol/l, p = 0.060, borderline signi­ficance), and PTH (15.5 ±6.8 pg/ml vs. 13.6 ±5.3 pg/ml, p = 0.066, borderline signi­ficance), while serum Mg2+ was significantly lower (0.81 ±0.09 mmol/l vs. 0.85 ±0.05 mmol/l, p = 0.021). In the ADPKD group we observed significant negative correlations of PTH with Ca²⁺ serum concentrations (Rs = –0.32, p = 0.025) and with estimated glomerular filtration rate (Rs = –0.31, p = 0.033).
Conclusions: The erythrocyte Ca²⁺ concentration is elevated in ADPKD patients with normal renal function. It may result from a dysfunction of mutated polycystins which can affect various aspects of electrolyte metabolism.