1,25 Dihydroxyvitamin D Testing and Its Clinical Significance

SPONSORED BY: DiaSorin, DiaSorin
C.E. CREDITS: P.A.C.E. CE | Florida CE
  • Head of the Center for Clinical Studies in Thoracic and Cardiovascular Surgery
      Prof. Dr. Armin Zittermann is Head of the Center for Clinical Studies in Thoracic and Cardiovascular Surgery at the Heart and Diabetes Center in Bad Oeynhausen, Germany. Prof. Zittermann also lectures at the Institute of Nutrition and Food Sciences at the University of Bonn on specific aspects of food security. His research focuses include the prevalence and the consequences of insufficient levels of vitamin D in humans, in particularly in patients with cardiovascular diseases. Furthermore, Prof. Zittermann investigates the confounding factors on outcomes of cardiac surgery patients, including the influence of immunosuppressants in heart transplant patients. His scientific work includes various fields such as biochemistry, physiology, epidemiology, nutrition, heart surgery and statistics. Prof. Zittermann has published more than 200 journal and book articles and has presented more than 250 lectures (national and international). He is a reviewer for a number of international scientific journals and serves on the editorial board of various nutritional medicine journals.


    1,25-dihydroxyvitamin D (1,25[OH]2D) is the active, hormonal form of vitamin D. It is produced from its precursor (vitamin D) by two hydroxylation steps in the liver and the kidneys. Circulating 1,25(OH)2D levels are regulated by serum calcium and phosphate concentrations, this is mediated by the calcium-regulating hormones, parathyroid hormone (PTH) and phosphate-regulating hormone, fibroblast growth factor-23 (FGF-23). In the human body, 1,25(OH)2D has a broad range of actions which include endocrine, autocrine and paracrine properties. Due to its picomolar concentrations and its lipophilic nature, 1,25(OH)2D is a difficult analyte and represents a challenge to the analytical biochemist with respect to quantification. Until recently, relatively large sample volumes and extensive purification and separation steps were required to quantify 1,25(OH)2D.

    The clinical relevance of circulating 1,25(OH)2D is underappreciated. Besides the well-known suppression of circulating 1,25(OH)2D in chronic kidney disease, evidence is accumulating that circulating 1,25(OH)2D is also reduced in other diseases. In addition, several studies have demonstrated that circulating 1,25(OH)2D is inversely associated with clinical outcome and may complement or substitute traditional laboratory tests. Nevertheless, in the clinical setting there are still several gaps in the present knowledge on circulating 1,25(OH)2D. These gaps include incomplete data about the effect of activated vitamin D or the influence of dosing and initial 25OHD level on circulating 1,25(OH)2D; and the effect of different diseases on circulating 1,25(OH)2D.

    In conclusion, circulating 1,25(OH)2D is less tightly regulated than assumed and may become a reliable predictor of clinical outcomes in some conditions.   

    Learning Objectives:

    1. Understand the role several hormones, including 1,25-dihydroxyvitamin D play in calcium and phosphate homeostasis.
    2. Understand why active vitamin D therapy should be accompanied by measuring 1,25 dihydroxyvitamin D.
    3. List the clinical conditions that would benefit from follow-up measurement for 1,25 dihydroxyvitamin D.


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