Enzyme immunoassay

To identify people at risk of vitamin D deficiency, serum 25-hydroxyvitamin D was measured. Fasting venous blood was collected at ages 14, 17, and 20 years. Serum was stored securely at −80°C. At 14 years, serum was measured using an enzyme immunoassay (Immunodiagnostic Systems Ltd.), and at ages 17 and 20, isotope-dilution liquid chromatography–tandem mass spectrometry was performed by RMIT Drug Discovery Technologies.²⁷ (link)

This was a retrospective observational study. The ethics committee at the Medical University of Graz approved the study before data retrieval and waived the requirement for informed consent because the investigators devised procedures to protect the confidentiality of the information to be collected. The primary endpoint was the prevalence of vitamin D deficiency and insufficiency. Secondary endpoints included the association of ICU mortality and hospital mortality with 25(OH) D status, adjusted for covariates like baseline Simplified Acute Physiology Score II (SAPS II), age, gender, glomerular filtration rate (GFR) and C-reactive protein (CRP). A subgroup analysis was performed in patients with available blood culture results during hospital stay. 25(OH) D was measured from fresh blood samples on workdays with enzyme immunoassay (Immunodiagnostic Systems, Boldon, UK) until June 2009 and with the IDS-iSYS, an assay based on chemiluminescence technology (Immunodiagnostic Systems), thereafter (R² 0.93 at our laboratory). The coefficient of variation for control material is 13% at 12 ng/ml, 10% at 31 ng/ml, and 9% at 64 ng/ml [26 (link)], respectively. Samples were taken in the early morning along with other routine laboratory tests. In the majority of patients, 25(OH) D was analysed within 48 hours following ICU admission.