25 oh vitamin d

Blood samples were collected after a 12h overnight fast. Biochemical measurements of calcium, glucose, glycated hemoglobin (HbA1c), total cholesterol and fractions (HDLc, LDLc), triglycerides, phosphorous, albumin, alkaline phosphatase, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatinine were performed on the day of blood collection. The serum aliquots for the other parameters were stored at −70 °C until the day of the assay. Calcium, phosphorus, alkaline phosphatase, fasting glucose, albumin, AST, ALT and creatinine were determined using an automatic biochemistry analyzer (Wiener lab, CT 600i, Thermo Fisher Scientific, Espoo, Finland). HbA1c and basal insulin levels were measured using an immunoenzymatic assay (Atellica^® CH, Siemens Heathineers, Erlangen, Germany). PTH, 25(OH) vitamin D and osteocalcin (Liaison, Diasorin, Saluggia, Italy) levels were measured using chemiluminescence. Leptin and Chemerin (Biovendor, R&D, Karásek, Czech Republic) were determined using ELISA. Serum insulin levels and HOMA-IR were assessed in 23 controls and 10 patients since DS individuals with type 2 diabetes using insulin therapy were not considered for these parameters. Insulin resistance was calculated using the HOMA-IR index: [fasting glucose (mg/dL) × 0.0555 × fasting insulin (µU/mL)/22.5], with normal values < 2.71 [45 (link)].

Serum levels of total calcium, albumin, 25-OH vitamin D (by radioimmunoassay, Diasorin, MN, USA), and PTH were measured before infusion. The sodium bicarbonate test was performed as previously described [6 (link), 7 (link)]. The volunteers were in fasting state for at least 4 hours and 35 mL/m² of body surface of 8.4% sodium bicarbonate solution was infused in one arm over 2 minutes and blood samples for the determination of serum PTH were drawn before (PTH₀) and at 3 (PTH_3 min), 5 (PTH_5 min), 10 (PTH_10 min), 30 (PTH_30 min), and 60 minutes (PTH_60 min) after the infusion of the other. Infusion of sodium bicarbonate causes acute metabolic alkalosis and in turn increases the binding of calcium to albumin leading to a decrease of the ionized calcium in blood [7 (link)]. No side effects were observed during the sodium bicarbonate infusion test except for a transient lips or/and hands paresthesia, metallic taste, and slight pain in the arm. However all these symptoms were transient and lasted about five minutes from the beginning of the infusion.