Liaison 25 oh vitamin d total assay

Fasting blood samples were collected between September 2002 and January 2006 and kept frozen at –80°C until analysis. Measurement of total serum 25(OH)D, including both vitamins D₂ and D₃, was processed on-site at the Icelandic Heart Association by means of a direct, competitive chemiluminescence immunoassay using the LIAISON 25 OH Vitamin D total assay (Diasorin, Inc.), hereafter referred to as vitamin D. The interassay CV was <6·5 % when using a frozen serum pool as a control sample and <12·7 % when using Liaison quality controls.

Blood was collected during the first clinic visit to AGES-study, from September 2002 to January 2006, and fasting serum samples were kept frozen at −80°C on-site in the IHA laboratory. Quantitative determination of total 25(OH) D (D₂ and D₃) was conducted by means of a direct, competitive chemiluminescence immunoassay (CLIA), using the LIAISON 25 OH Vitamin D Total assay (DiaSorin, Inc., Stillwater, Minnesota). The inter assay coefficient of variation was <6.5%, using a previously frozen serum pool as the control sample and <12.7% when the calculated data were from measurements using Liaison quality controls.

During the study period, serum 25(OH)D levels were measured by routine clinical analysis. Before 2008 (n = 196 samples), both a chemiluminescence immunoassay (CLIA) (Nichols Institute Diagnostics, California, USA) and a radioimmunoassay (Immunodiagnostics Systems, Boldon, UK) were used, due to a change in clinical diagnostic operating procedures. Both methods had a good inter-assay correlation.[8 (link)] After 2008 (n = 358 samples), a CLIA (LIAISON® 25 OH Vitamin D TOTAL Assay, Diasorin, Saluggia, Italy) was used.
In accordance with other studies, 25(OH)D data were deseasonalized to corrrect for seasonal variation of 25(OH)D levels.[17 (link), 31 (link), 32 (link)] The total of all consecutive 25(OH)D levels from all patients were used to model seasonal variation in our cohort according to the sinusoidal model described by van der Mei et al.[17 (link)] yt = β0 + β1sin(2πt/365)+ β2cos(2πt/365), where yt denotes serum 25(OH)D concentration, t denotes the day of the year when the sample was collected, and βj (j = 0,1,2) are estimated regression coefficients. The adjusted 25(OH)D value was calculated by applying the deviation of an individual from the population mean at a time-point measured, on the population mean at T = 0. The seasonal corrected 25(OH)D levels are referred to as vitamin D status.

Blood samples from neonates were obtained from the cord blood and drawn into BD Vacutainer® SST (BD) tubes. At 28 days of life and at 4 months, the blood samples of the PTs were obtained from a peripheral vein as part of the routine protocol followed in the unit to monitor metabolic status. No extra blood volume was required. Maternal blood samples were obtained from a peripheral vein in the delivery room after the mothers had given informed written consent. The blood collected into these tubes was allowed to clot in the cold for 30 min prior to centrifugation at 1500 x g for 10 min at 4 °C. Once centrifugated, the samples were separated into aliquots and frozen at − 80 °C until analysis. Serum levels of 25(OH) D were measured by Radioimmunoassay (RIA), using an immunological test kit (LIAISON® 25 OH Vitamin D TOTAL Assay; DiaSorin), following the manufacturers’ instructions with the PACKARD Copper II E5005 gamma counter analyzer.
Parathyroid hormone (PTH) was measured by immunoradiometric assay by our CAS. MMP-8 were quantified by a semi-automated TRITURUS®-200 open-configuration kit that uses Xmap technology as a basis, designed for determinations by the sandwich ELISA (enzyme-linked immunosorbent assay) technique, using a 450-nm microplate reader with capacity for automatic dispensing of samples/reagents and reading of results directed by computer.