Endocrine Abstracts

The total 25-hydroxy-vitamin-D (t-25OHD) level reflects the vitamin-D supply, but it is also influenced by the levels of vitamin-D-binding-proteins (DBP) and albumin. The type of dialysis influences the levels of serum proteins. The ‘free-hormone hypothesis’ states that only the free molecules (f25OHD) can diffuse intracellular. Our aim was to evaluate the total, calculated (c-f25OHD) and direct measured (dm-f25OHD) 25OHD levels in patients with chronic renal disease on cholecalciferol.

Methods: 100 patients [45 men; 55 women; 69±14 years: 40 on haemodialysis (HD), 26 chronic renal failure (CRF) both on 1000 IUD₃/day; 34 on peritoneal dialysis (PD) on 3000 IUD₃/day] were investigated. Their sera were analysed for DBP (Dako), albumin, Ca, PTHi, t-25OHD (Roche), dm-f25OHD (DIAsource).

Results: Albumin levels were significantly lower (PD:38±5 HD:40±5; CRF:43±3 g/l; P<0,001) and DBP concentrations higher (390±55 CRF:352±42; HD:323±61 mg/l; P<0,001) were in PD group. The t-25OHD and c-f25OHD were the lowest in PD (t-25OHD: 65±30; CRF:78±38; HD:79±45 nmol/l, c-f25OHD: 14±7; CRF:18±9; HD:20±11 pmol/l, P<0.05). There were no significant differences among dm-f25OHD levels (PD:16±5; CRF:16±6; HD:15±6 pmol/l). The highest incidence of suboptimal vitamin D supply was found in PD patients on the bases of t-25OHD (PD:65%; CRF:42%; HD:43%) and also in c-f25OHD levels. These incidences decreased significantly into 15%–23%, when dm-f25OHD was taken into consideration. Out of the three 25OHD fractions only dm-f25OHD levels gave the opportunity to prove significant relationship between PTHi/Ca and 25OHD level (OR=3.8_{CI:1.024-14.4}; P=0.036).

Conclusions: t-25OHD and c-f25OHD values underestimate the vitamin D supply particularly in PD patients. Patients on PD need much higher doses of cholecalciferol, without any differences from other two groups in dm-f25OHD levels either. Patients, who have higher dm-f25OHD level have 3.8 times higher chance for normal Ca/PTHi levels. In case of dm-f25OHD there was a significant relationship proven between 25OHD level and related biomarkers. The dm-f25OHD seems to be a reliable marker for estimation of vitaminD supply in patients with chronic renal disease.