Review Vitamin D: Methods of 25 hydroxyvitamin D analysis, targeting at risk populations and selecting thresholds of treatment Paul Glendenning a, b, c, ⁎, Charles A. Inderjeeth b, d a Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Australia b School of Medicine and Pharmacology, University of Western Australia, Australia c School of Pathology and Laboratory Medicine, University of Western Australia, Australia d Area Rehab and Aged Care, North Metropolitan Health Service, Australia abstract article info Available online 11 April 2012 Keywords: Vitamin D Methods of 25OHD analysis 25OHD target of treatment Interest in vitamin D has intensified with the association of vitamin D deficiency (VDD) with many diseases. This review will outline the limitations of current 25 hydroxyvitamin D (25OHD) methods, the target treat- ment threshold, and review the classical (endocrine/bone) and non-classical (paracrine/non-bone) actions of vitamin D. Recent standardisation by the National Institutes of Standards and Technology and use of LC tandem mass methodology has reduced inter-method bias but insensitivity and imprecision of automated methods have challenged assay performance. Many diseases are associated with VDD but randomised clinical trial data demonstrating the benefit of un-activated sterol supplementation only exists for the prevention of falls and fractures. Consequently, 25OHD measurement should be restricted to high falls or fracture risk patients. Controversy regarding the 25OHD target of therapy requires consensus. Until resolved, widespread adoption of screening programmes and measurement of 25OHD in patients at risk of non-musculoskeletal disease is premature, costly and not supported by evidence. © 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901 Defining vitamin D deficiency: setting target 25OHD levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 Biochemical markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 Bone effects: BMD, fracture and bone biopsy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 Falls risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 Adopting the optimal 25OHD target threshold — ambiguity and differing consensus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 Target populations: when to measure 25OHD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 Disease associations: endocrine and autocrine effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 Measuring 25OHD — methodological issues of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904 Reference methods and reference standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905 Introduction Vitamin D is an important endocrine hormone with well charac- terised effects on bone and muscle development in early life as well as preservation of musculoskeletal function in later life. Other associations between vitamin D deficiency and non-musculoskeletal disease include cancer, cardiovascular disease, immune dysfunction, neurological dis- ease, metabolic and infective illness and are less well characterised and largely based on observational studies. Randomised clinical trial (RCT) data demonstrating the benefit of vitamin D supplementation with un-activated sterol therapy (cholecalciferol or ergocalciferol) only exists for the prevention of falls or fractures [1,2]. The best charac- terised musculoskeletal consequences of vitamin D deficiency are oste- oporosis, osteomalacia, muscle strength and falls risk. Clinical Biochemistry 45 (2012) 901–906 ⁎ Corresponding author at: Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Australia. E-mail address: Paul.Glendenning@health.wa.gov.au (P. Glendenning). 0009-9120/$ – see front matter. © 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.clinbiochem.2012.04.002 Contents lists available at SciVerse ScienceDirect Clinical Biochemistry journal homepage: www.elsevier.com/locate/clinbiochem