The role of calcium metabolism disorders in the formation of different density calculi with calcium oxalate nephrolithiasis

Abstract

Objective To investigate the relationship between calcium metabolism disorders, stone formation inhibitor levels and stone density in primary and recurrent calcium-oxalate nephrolithiasis.Material and Methods Sixty nine patients with urolithiasis were examined, their average age was 41,4 ± 9,5 years. Two main groups were distinguished: Group 1 – primary calcium-oxalate nephrolithiasis (PN), Group 2 – recurrent calcium-oxalate nephrolithiasis (RN). Then each group was divided into two subgroups – A and B according to stone density: 500–1000 HU and from 1000–1500 HU, respectively. Stone density was determined by computed tomography (CT). PTH (parathormone), PTHrP (parathyroid hormone related protein), vitamin D, total blood calcium (Ca), ionized blood Ca, total blood protein, Ca and urine pH were also examined. After the examination, patients underwent surgical removal of the stones.Results It was found that 41.9% of group 1 and 46.9% of group 2 patients had grade I obesity. Average creatinine level in group 2 was 9.7% higher than in group 1 (p < 0.05). Urea level in both groups was not statistically significantly different. Glomerular filtration rate (GFR) was comparable. Groups 2A and 2B had higher PTHrP values (77.61 and 76.98 pg/mL, respectively) combined with relatively high PTH levels (2A – 4.4 pg/mL and 2B – 5.1 pg/mL), relatively low osteopontin concentration (2A – 0.044 pg/ mL, 2B – 1.106 pg/mL), compared to those in group 1 (p < 0.05). Pairwise unidirectional differences between groups 1A and 2A, 1B and 2B were found to correlate positively with density values: for osteopontin: r = 0.992 (p < 0.05); for vitamin D: r = 0.831 (p < 0.05); for blood Ca2+ ions: r = 0.836 (p < 0.05); for urine pH: r = 0.863 (p < 0.05). There was a negative correlation with the daily concentration of urinary calcium ions with the density of concrements: r = -0.663; p < 0.05. The concentration of osteopontin was significantly higher in Group 1B and 2B patients, and it was significantly lower in patients with stones of < 1000 HU density. Higher values of osteopontin concentration were noted in groups 1B and 2B in relation to groups 1A (p < 0.05) and 2A (p < 0.05). The increase of blood Ca2+ ions in patients in groups 1B and 2B in relation to groups 1A (p < 0.05) and 2A (p < 0.05) was also accompanied by higher values of vitamin D.Conclusion Patients with denser stones showed high values of osteopontin and PTHrP in serum and low values of urinary calcium ions, which may lead to the formation of concrements on the matrix with an organic base. Determination of calcium metabolism makes it possible to predict recurrence of KSD in primary calcium oxalate nephrolithiasis and assess the severity of mineral metabolism disorders in recurrent calcium oxalate nephrolithiasis.