Endocrine Abstracts

The total 25-hydoxy-vitamin-D (t25OHD) level can be assessed by various methods and reflects vitamin D intake. Results are influenced by the serum variables affected by dialyses.

Aims: To examine t25OHD and bioavailable vitamin D (b25OHD) by two methods in patients on peritoneal-(PD) and hemodialysis (HD).

Methods: We studied 37 HD (64±15 years) and 36 PD (63±18 years) patients. The t25OHD was assessed by chemiluminescence immunoassay (LIA) and electrochemiluminescence protein binding assay (PBA). Levels of PTH-biointact (PTHbi) by immunometric assay, vitamin D binding protein (DBP) by turbidimetry and albumin by colorimetry were measured. The b25OHD values were calculated.

Results: t25OHD values below the analytical sensitivity occurred more frequently by PBA (29%) than by LIA (1.4%). Values of t25OHD (LIA: 23±8 vs 37±15; PBA: 11±6 vs 37±19 nmol/l) and b25OH (LIA: 2.1±1.5 vs 4.7±5.1; PBA: 1.0±0.7 vs 4.8±5.8 nmol/l) were lower in PD, but PTHbi levels were lower in HD (150±92 pg/ml) than in PD (287±152 pg/ml; P<0.001). Albumin levels were lower in PD (38±5 vs 41±4 g/l; P<0.01), but DBP levels were higher in PD than in HD (339±102 vs 291±112 mg/l; P<0.05). Positive correlations were observed with both methods between t25OHD and albumin levels in PD (PBA: r=0.36; P<0.05; LIA: r=0.48; P<0.01). The correlations of t25OHD levels assessed by LIA and BPA were different (HD: r=0.89; P<0.001; PD: r=0.47, P<0.01), but correlations of b25OHD values were similar (HD: r=0.85; PD: r=0.83, P<0.001) in both groups. Negative correlations were observed between PTHbi and t25OHD levels (PBA: r=−39, LIA: r=−0.42; P<0.05) in HD only, but between PTHbi and b25OHD were similar in both (LIA: PD r=−0.40, HD r=−0.54, P<0.01; PBA: PD r=−0.49, HD r=−0.44).

Conclusions: Assessment of vitamin D supply by LIA and PBA is influenced by lower albumin levels especially in PD. Estimation of b25OHD is more suitable in PD, but t25OHD is reliable by both methods in HD.