Is low plasma 25-(OH)vitamin D a major risk factor for hyperparathyroidismand Looser's zones independent of calcitriol?

Background. Recent reports suggest that calcitriol might not be the sole ac tive metabolite of vitamin D and that plasma concentrations of 25-(OH)vitam in D (25OHD) are often abnormally low in hemodialysis patients. We have the refore evaluated plasma 25OHD as a risk factor for parathyroid hormone (PTH ) hypersecretion and radiological bone disease. We carried out a cross-sect ional study during the month of September in an Algerian dialysis center of 113 patients who were not taking supplements of alphacalcidol or calcitrio l. Methods. Plasma 25OHD, calcitriol, PTH, calcium, phosphate, bicarbonate, an d aluminum were measured, and x-rays of the hands and pelvis were obtained for evaluation of subperiosteal resorption and Looser's zones. Results. The median plasma 25OHD was 47.5 nmol/liter (range 2.5 to 170.0). Univariate analysis showed that plasma PTH was correlated positively with m onths on maintenance dialysis and negatively with plasma 25OHD, calcitriol, calcium, bicarbonate and aluminum, but not with that of phosphate. plasma 25OHD was positively correlated with calcium and calcitriol. Using multiple regression analysis, only plasma 25OHD (negative) and the duration on main tenance dialysis (positive) were independently linked to plasma PTH. The pr evalence of isolated subperiosteal resorption (ISR) was 34%, and that of th e combination of resorption with Looser's zones (CRLZ) was 9%; thus, only 5 7% of the patients had a normal x-ray appearance. These groups were compara ble with regards to age, gender, and duration on dialysis. When the biochem ical measurements of the patients with CRLZ were compared with those from p atients without radiological lesions, plasma 25OHD was the only parameter t o show a statistically significant difference, being significantly lower in the CRLZ group (26 +/- 18 vs. 57 nmol/liter, ANOVA, P < 0.004). Plasma 25O HD was also significantly lower in the ISR group (44, P < 0.05) than in the normal x-ray group, and plasma Ca (P < 0.003) and bicarbonate (P < 0.02) w ere lower. Logistical analysis showed that the presence of resorption was i ndependently linked only with plasma PTH. Looser's zones and subperiosteal resorption were not seen in patients with plasma 25OKD of more than 40 (Loo ser's zones) and more than 100 nmol/liter (subperiosteal resorption). The o ptimal range for intact PTH in hemodialysis patients with mild aluminum ove rload is 10 to 25 pmol/liter. We found that plasma PTH was inappropriately high only when plasma 25OHD was less than 100 nmol/liter. With a plasma 25O HD of between 100 and 170 nmol/liter, hypercalcemia was present with a plas ma PTH of less than 10 pmol/liter in only one case. Conclusions. This cross sectional study shows that low plasma 25OHD is a ma jor risk factor for hyperparathyroidism and Looser's zones. In dialysis pat ients, we suggest that the plasma levels of 25OHD are maintained around the upper limit of the reference range of sunny countries.