Prevalence of vitamin D deficiency and consequences for PTH reference values M.M.L. Deckers a, ⁎, R.T. de Jongh b , P.T.A.M. Lips b , B.W.J.H. Penninx c , Y. Milaneschi c , J.H. Smit c , N.M. van Schoor d , M.A. Blankenstein e , A.C. Heijboer e a Dept. Clinical Chemistry Saint Lucas Andreas Hospital, Amsterdam, The Netherlands b Dept. Internal Medicine, VU University Medical Center, The Netherlands c Dept. Psychiatry, VU University Medical Center, The Netherlands d Dept. Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands e Dept. Clinical Chemistry, VU University Medical Center, The Netherlands abstract article info Article history: Received 30 May 2013 Received in revised form 6 August 2013 Accepted 28 August 2013 Available online 4 September 2013 Keywords: PTH Vitamin D Reference value BMI Reference values of PTH depend on vitamin D status of the reference population. This is often not described in package inserts. The aim of the present study was therefore to calculate assay specific PTH reference levels in EDTA plasma for the Architect (Abbott) in relation to 25-hydroxyvitamin D (25OHD) levels. The relation between PTH levels, 25OHD, BMI, age, gender and kidney function was determined in a cohort of older individuals from the Longitudinal Aging Study Amsterdam (LASA, n = 738, age 55–65 years) and in a cohort of healthy individuals from the Netherlands Study of Depression and Anxiety (NESDA, n = 633, 18–65 years). The LASA cohort is a representative sample of the Dutch older population. As expected, PTH reference values were significantly lower in 25OHD sufficient subjects (25OHD N 50 nmol/L) than in 25OHD deficient and insufficient subjects. The 97.5th percentile of PTH in 25OHD sufficient subjects was 10 pmol/L (94.3 pg/mL), which was higher than the upper limit stated by the manufacturer (7.2 pmol/L or 68.3 pg/mL). The relation between vitamin D and PTH was independent of age, gender, BMI and kidney func- tion. In conclusion, we have shown that it is important to establish PTH reference values in a local reference pop- ulation taking 25OHD status into account. © 2013 Published by Elsevier B.V. 1. Introduction Standardization of PTH assays is lacking. Method comparison studies of PTH immunoassays from various suppliers show 2–3 fold differences in PTH levels [1–4]. The lack of standardization has major clinical impli- cations as PTH is used not only to exclude hyper- or hypoparathyroidism but also to monitor disease progression in patients with Chronic Kidney Disease (CKD) [2,5–7]. To overcome these problems either a standardization program should be started or assay specific reference values or assay specific decision limits should be used [8,9,4]. In order to define assay specific reference values a proper description of the population characteristics such as age, gender, race, BMI and vitamin D levels is required [10]. These characteristics are often poorly described in the package inserts [9]. Recent studies have shown that 1–14% of the variation in PTH levels is explained by vitamin D status [11,12]. Given the inverse relationship between PTH and 25-hydroxyvitamine D (25OHD), 25OHD levels should be simultaneously assessed while defining PTH reference values [10,13]. Or alternatively, only vitamin D sufficient subjects should be included in the reference population [9,11]. The aim of the present study was to examine the association be- tween 25OHD levels and PTH in two large, healthy cohorts and calculate assay specific PTH reference levels on the Architect (Abbott) in EDTA plasma in relation to 25OHD levels. 2. Material and methods 2.1. Methods 2.1.1. Subjects The LASA study is based on an age and sex-stratified representative healthy sample of Dutch, mainly Caucasian, older population as de- scribed earlier [14,15]. In this study the baseline measurements of the second cohort were included. The samples from the LASA were col- lected in 2002. Blood samples were obtained in the morning after light breakfast without dairy products. The samples were centrifuged and Clinica Chimica Acta 426 (2013) 41–45 Abbreviations: NESDA, Netherlands Study of Depression and Anxiety; LASA, Longitudinal Aging Study Amsterdam; KDIGO, Kidney Disease: Improving Global Outcomes; KDOQI, National Kidney Foundation-Kidney Disease Outcomes Quality Initiative; CKD, Chronic Kidney Disease; CKD-MBD, Chronic Kidney Disease Mineral and Bone Disorder; GFR, Glomerular filtration rate; 25OHD, 25-hydroxyvitamin D; PTH, parathyroid hormone; BMI, body mass index. ⁎ Corresponding author. Tel.: +31 20 5108342; fax: +31 20 6183976. E-mail address: m.deckers@slaz.nl (M.M.L. Deckers). 0009-8981/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.cca.2013.08.024 Contents lists available at ScienceDirect Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim