Table of Contents
Epidemiology Research International
Volume 2015 (2015), Article ID 581206, 8 pages
http://dx.doi.org/10.1155/2015/581206
Research Article

Quality Assessment of 25(OH)D, Insulin, Total Cholesterol, Triglycerides, and Potassium in 40-Year-Old Frozen Serum

1Section for Epidemiology and Social Medicine, Institute of Medicine, University of Gothenburg, P.O. Box 453, 405 30 Gothenburg, Sweden
2Sahlgrenska Biobank, Sahlgrenska University Hospital, 413 45 Gothenburg, Sweden
3Department of Biomedicine, Sahlgrenska Academy, University of Gothenburg, 413 45 Gothenburg, Sweden
4Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, University of Gothenburg, 431 80 Mölndal, Sweden
5UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK
6Department of Primary Health Care, Institute of Medicine, University of Gothenburg, 405 30 Gothenburg, Sweden

Received 1 November 2014; Revised 26 January 2015; Accepted 28 January 2015

Academic Editor: Jaume Marrugat

Copyright © 2015 Monica Leu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background. Many longitudinal epidemiological studies collect specimens into biobanks to investigate how biomarkers predict future disease. In 1968-1969, the Population Study of Women in Gothenburg (PSWG) established a biobank of serum samples. Objective. To examine the validity of 25-hydroxyvitamin D (25(OH)D), total cholesterol, triglycerides, insulin, and potassium after 40 years of storage at −20°C in terms of relative and absolute agreement. The quality of these markers under such condition has not been previously investigated. Methods. Baseline and remeasured levels were compared in selected samples through percentage change, correlation, and regression. 25(OH)D levels, not assessed at baseline, were compared by season, by BMI, and longitudinally over six years. Results. Despite some lack of absolute agreement, Spearman correlations were >0.7 and statistically significant for all biomarkers. The 1968-1969 25(OH)D correlated with BMI and with levels six years later . Summer 25(OH)D was higher than winter 25(OH)D . Conclusion. For all markers, baseline and remeasured levels exhibited high relative agreement. 25(OH)D was comparable with expected levels on fresh blood and varied with season. In future studies, PSWG individuals will be ranked according to these markers in order to predict incidence of disease.