Liaison chemiluminescence immunoassay

The women were randomized 1:1, between 10–18 weeks of gestation, to a daily intake of 4,000 IU vitamin D₃ plus a multivitamin containing 400 IU vitamin D₃ or a matching placebo tablet plus a multivitamin containing 400 IU vitamin D₃, i.e. 4,400 vs. 400 IU vitamin D₃ supplement per day. The intervention was continued until delivery. Adherence was measured by MEMS^® (Medication Events Monitoring Systems) caps, an electronic cap that recorded each time the tablet container was opened[7 (link)].
Blood was drawn from the mothers at entry to the trial and at the 3^rd trimester visit (32 to 38 weeks of gestation) for measurement of circulating levels of 25(OH)D, determined by using the DiaSorin Liaison® chemiluminescence immunoassay[13 (link)].

Laboratory blood tests included 25-OH vitamin D3, PTH, and ALP levels. 25-OH Vitamin D3 was measured by radioimmunoassay using a gamma counter (Hewlett Packard, Palo Alto, CA, USA). PTH was measured using a LIAISON chemiluminescence immunoassay (Diasorin, Stillwater, MN, USA), and ALP was measured using an enzyme assay using a Hitachi Automatic Analyzer 7600 (Hitachi, Tokyo, Japan) and external and internal quality controls.
Bone mineral density (BMD) (g/cm²) was measured by DEXA scan (DISCOVERY-W fan-beam densitometer; Hologic Inc., Bedford, MA, USA). The accuracy of BMD in KNHANES was assessed by educated affiliated osteoporosis assessors, and interpretation of the BMD results was corrected and standardized by quality control [24 (link)].
BMD was estimated at lumbar vertebrae (L1–4) and the femur (total femur and femoral neck). The T-score, which is a reference standard deviation value, compared with BMD of a healthy 30-year-old, was used to compare BMD between groups. Osteoporosis was defined when the T-score was ≤ −2.5, and a T-score > −2.5 but < −1 was classified as osteopenia [25 (link)].