A comparison of automated methods for the quantitation of serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D Samantha M. Kimball a, ⁎ , Reinhold Vieth a,b a Department of Nutritional Sciences, University of Toronto, Canada M5S 3E2, Department of Laboratory Medicine and Pathology, Mt. Sinai Hospital, Toronto, Canada M5G 1X5 b Department of Laboratory Medicine and Pathology, University of Toronto, Canada M5S 3E2 Received 17 April 2007; received in revised form 1 July 2007; accepted 24 July 2007 Available online11 August 2007 Abstract Objective: To compare automated platforms with the routinely used methods in our clinical laboratory for the quantitation of 25- hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D]. Method: The NEXgen Four and Triturus ELISA platforms, utilizing the IDS enzyme immunoassay (EIA) kit for 25(OH)D, and the DiaSorin Liaison 25(OH)D methods were compared with the DiaSorin radio immunoassay (RIA) kit. The NEXgen Four and the Triturus, utilizing IDS EIA for 1,25(OH)2D, were compared with the thymus radioreceptor assay (RRA) for measurement of 1,25(OH)2D. Results: NEXgen correlated best with DiaSorin RIA (r 2 = 0.652). NEXgen correlated best with the thymus RRA method (r 2 = 0.541). Imprecision CV values for NEXgen 1,25(OH)2D were 2.8–9.4% within-run and 10.2–13.9% between-run compared with a between-run precision of 14.0–16.9% with the thymus RRA method. Conclusion: NEXgen correlated best with DiaSorin RIA for measurement of 25(OH)D. NEXgen correlated best and demonstrated better precision than thymus RRA for quantitation of 1,25(OH) 2D. © 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. Keywords: Automation; Vitamin D; 25-Hydroxyvitamin D; 25(OH)D; 1,25-dihydroxyvitamin D; 1,25(OH)2D; NEXgen; Triturus; Liaison Introduction Vitamin D (cholecalciferol) is a 27-carbon seco-steroid that is metabolized in the body to many metabolites. The two clinically relevant compounds produced are 25-hydroxyvitamin D [25(OH)D or calcidiol], the accepted measure of vitamin D nutritional status [1] and 1,25-dihydroxyvitamin D [1,25(OH) 2D or calcitriol], the active metabolite involved in calcium homeostasis. Clinical laboratories have published a vast array of methods for determining concentrations of vitamin D metabolites, however the results obtained between laboratories were reported to be inconsistent with large inter-laboratory variation [2–4]. In 1989, the International External Quality Assessment Scheme for Vitamin D metabolites (DEQAS) was established to ensure analytical reliability of 25(OH)D assays and was extended to cover 1,25(OH)2D assays in 1997 [5]. Clinical demand has increased the need for simple, rapid methods for determining 25(OH)D concentrations in patient samples. Currently, various commercial kits are available for 25(OH)D determination including DiaSorin (Stillwater, MN) Radio- immunoassay (RIA), Immunodiagnositic Systems (IDS) Ltd. (Tyne and Wear, UK) RIA, IDS Enzyme Immunoassay (EIA), DiaSorin Liaison (Stillwater, MN) automated platform and the Nichols Advantage (San Clemente, CA) automated chemilu- minescence assay. Selective antibodies are incorporated in the DiaSorin and IDS Ltd. 125 I-based RIAs, IDS uses a non- radioactive enzyme in the IDS EIA kit, while DiaSorin employs a competitive chemiluminescence immunoassay on the Liaison platform, whereas the Nichols Advantage utilizes a competitive protein-binding assay incorporating chemiluminescence. The Available online at www.sciencedirect.com Clinical Biochemistry 40 (2007) 1305 – 1310 ⁎ Corresponding author. 600 University Ave. Room 6-423, Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, ON Canada M5G 1X5. Fax: +1 416 586 8504. E-mail address: samantha.kimball@utoronto.ca (S.M. Kimball). 0009-9120/$ - see front matter © 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.clinbiochem.2007.07.015