Guiding Appropriate Laboratory Test Utilization: 1,25-OH-Vitamin D

The integral nature of vitamin D in human physiology has recently gained great interest and popularity in modern medicine. Accordingly, use of military laboratory services to measure vitamin D has increased markedly and maintains high visibility, both as a nutritional monitor and a significant cost center. At San Antonio Military Medical Center (SAMMC), over 53K requests for vitamin D analysis were processed in fiscal year (FY) 2014, with cumulative costs exceeding $400K. With this volume being among the highest for a single test processed in the facility, reviews were undertaken to identify deviations in appropriate utilization as well as ways to reduce overall costs. Recognizing inappropriate utilization patterns begins with having a comprehensive understanding of the background physiology of this vitamin. This editorial seeks to briefly review essential physiology of vitamin D and offer potential suggestions other facilities may consider to improve utilization. Vitamin D is a group of related steroids recognized as essential in an array of physiological processes, of which calcium homeostasis is the most understood. Vitamin D precursors are primarily obtained through two sources: endogenous synthesis and diet. Endogenously, cholecalciferol (vitamin D3) is formed from 7-dehydrocholesterol in the skin upon exposure to ultraviolet B rays in sunlight. In contrast, dietary sources of vitamin D are primarily obtained in the form of vitamin D3 (through animal sources) and/or as ergocalciferol (vitamin D2), the primary precursor found in plants. In the liver, vitamin D2 and vitamin D3 are metabolized to 25-hydroxy vitamin D (25-OH-D; calcidiol) and made available as a circulating storage pool with a half-life of 2 to 3 weeks. In a process tightly regulated by circulating levels of parathyroid hormone, calcium, and phosphate, 25-OH-D is subsequently converted in the kidney to its bioactive form 1,25-hydroxy vitamin D (1,25-OH-D; calcitriol). This hormone possesses circulating concentrations approximately 1,000-fold lower than the storage form (25-OH-D) and with a much shorter half-life of 4 to 6 hours. Through activation of intestinal active transport systems, 1,25-OH-D increases absorption of calcium and phosphate, subsequently increasing the plasma concentration of these essential minerals. It is beyond the scope of this editorial to address the need for comprehensive vitamin D screening, although the reader may be referred to a recent U.S. Preventative Services Task Force recommendation for recent advances in this field. During routine review of a reference laboratory billing statement, a major deficiency was identified at SAMMC: an unexpectedly high number of 1,25-OH-D orders placed by nonspecialty health care providers (HCPs). In FY 2014, we found that over 1,300 1,25-OH-D were ordered by HCPs, with over 95% originating from nonspecialty clinics (e.g., Family Medicine). Examining these cases, we observed that virtually none of these requests appeared to be ordered on patients that were being investigated for an overt calcium disorder. Moreover, based on the situational context, it was abundantly clear that these orders were placed to merely screen patients for vitamin D deficiency. Based on its significantly longer half-life, its status as an abundant circulating pool, and the less immediate impact of physiological controls on its concentration, 25-OH-D is the most effective marker for assessing nutritional status, a fact supported by the most recent clinical guidelines. In contrast, measurement of 1,25-OH-D is best suited for use in the sequential assessment of complex calcium/phosphate disorders. In FY 2015, we implemented utilization controls on this test, both to reduce unnecessary overhead costs as well as improve test utilization and subsequent patient care. To maximize the effect of this program, we employed a multidimensional strategy similar to those published by peer academic facilities: