Analytical, experimental and clinical aspects of total 25-hydroxyvitamin D measurement by two ligand assays are differentially biased by disease-related factors.

BACKGROUND: Pathological concentrations of plasma proteins may confound the results of binding assays. We compared two routinely used total 25-hydroxyvitamin D [t-25(OH)D] methods: a chemiluminescence-immuno-(CLIA) and an electro-chemiluminescence-protein-binding-(ECLPBA) assay. METHODS: Two sub-studies were performed: 1) In an "in vitro" study, exogenous albumin was added to pools of patients' sera with low albumin levels; and 2) In "ex vivo" studies of Cohort_1: sera of hospitalized patients with low albumin levels, and of healthy controls; and of Cohort_2: outpatients with chronic kidney disease in pre-dialysis stage, or on peritoneal dialysis and hemodialysis were investigated by the routine and LC_MS/MS methods. RESULTS: When increasing albumin concentrations were "in vitro" added, t-25(OH)D levels were overestimated by ECLPBA, and underestimated by CLIA. In patients' sera, positive correlations were detected between t-25(OH)D-vitamin D binding protein (DBP) values by both routine methods, and between t-25(OH)D-albumin values by all three methods. Much higher t-25(OH)D was measured by LC_MS/MS in all subgroups. When altering albumin levels with constant DBP concentration, the "in vitro" experiment revealed a higher sensitivity of ECLPBA. The "ex vivo" measurements demonstrated clinically relevant differences between the routine methods. CONCLUSION: Both routine methods are dependent of the matrix effect in hospitalized patients, which is predicted by the DBP/Albumin ratios. In hemodialysis, ECLPBA is recommended because its outcomes differ less from those of LC_MS/MS. The results of LC_MS/MS are reliable, but not routinely available. A guidance would be valuable on how levels measured by the binding methods differ from those by LC-MS/MS in various clinical conditions.

[Clinical value of two methods to measure parathyroid hormone in chronic renal insufficiency, considering vitamin D metabolism]. / Kétféle parathormonmérési módszer klinikai értékének vizsgálata krónikus veseelégtelenségben a D-vitamin-ellátottság figyelembevételével.

INTRODUCTION: Parathyroid hormone levels provide important information in chronic renal failure. AIM: To compare parathyroid hormone levels measured by two assays in correlation with vitamin D supply. METHOD: Parathyroid hormone and 25-hydroxi-vitamin-D were determined in 104 patients (31 patients with chronic renal failure without renal replacement therapy, 36 patients treated with peritoneal dialysis and 37 patients treated with hemodialysis). RESULTS: Good correlation was found between results of the two parathyroid hormone methods, but the intact parathyroid hormone levels were higher than the biointact values. 87% and 13% of the patients had vitamin-D deficiency and insufficiency, respectively. The frequency of serious vitamin-D deficiency was higher in the peritoneal dialysis than in the hemodialysis group. Intact parathyroid hormone levels were different in dialysed patients having vitamin-D-deficiency and insufficiency, and the difference was higher for the biointact than intact values. Negative correlation was detected between biointact parathyroid hormone and 25-hydroxivitamin-D in the hemodialysis group. CONCLUSIONS: Biointact parathyroid hormone levels better reflect the vitamin D supply and bone metabolism than intact levels, especially in hemodialysed patients.

[Vitamin D supply among healthy blood donors in Vas County, Hungary]. / D-vitamin-ellátottság felmérése Vas megye egészséges véradói körében.

INTRODUCTION: There is growing evidence showing the importance of adequate vitamin D supply for preserving health. AIM: The aim of the study was to evaluate the vitamin D supply among healthy blood donors and healthy elderly subjects in County Vas, Hungary. METHODS: Serum 25-hydroxyvitamin D, intact parathyroid hormone, calcium and albumin (Cobas, Modular, Roche), as well as serum alfa-2-globulin concentrations (Gelelfo, Interlab) were determined in 178 serum samples (68 men, 110 women, 41 were taking oral contraceptives). The results were analysed according to sex and age (younger and older than 43 years), and the impact of oral contraceptive use was also taken into consideration. RESULTS: Deficiency and insufficiency in vitamin D levels were detected in 9.6% and 32% of the studied subjects, respectively, whereas sufficient vitamin D levels were present in 58.4% of the subjects. 63% of the older and 41.2% of the younger group had suboptimal vitamin-D supply (p < 0.01). In women taking oral contraceptives serum 25-hydroxyvitamin D and alfa-2-globulin levels were significantly higher, whereas serum albumin and calcium levels were lower than in the control group. There was no difference in serum intact parathyroid hormone concentration between oral contraceptive users and non-users. CONCLUSIONS: The occurrence of suboptimal vitamin D supply is significant, although less frequent than that in literature reports. In women taking oral contraceptives, serum 25-hydroxyvitamin D levels were higher, but serum intact parathyroid hormone concentrations were not decreased suggesting that the increased 25-hydroxyvitamin D levels may be the consequence of oestrogen-induced alterations of serum protein fractions.