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LETTER TO THE EDITOR
Year : 2014  |  Volume : 18  |  Issue : 2  |  Page : 246

Response to the editorial on "Defining vitamin D deficiency, using surrogate markers"


1 Department of Laboratory Sciences, Tata Medical Center, Rajarhat, Kolkata, India
2 Department of Digestive Diseases, Tata Medical Center, Rajarhat, Kolkata, India

Date of Web Publication19-Mar-2014

Correspondence Address:
Subhosmito Chakraborty
Department of Laboratory Sciences, Tata Medical Center, 14 MAR (EW), Rajarhat, Newtown, Kolkata - 700 156
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2230-8210.129124

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How to cite this article:
Chakraborty S, Mallath MK. Response to the editorial on "Defining vitamin D deficiency, using surrogate markers". Indian J Endocr Metab 2014;18:246

How to cite this URL:
Chakraborty S, Mallath MK. Response to the editorial on "Defining vitamin D deficiency, using surrogate markers". Indian J Endocr Metab [serial online] 2014 [cited 2019 Dec 5];18:246. Available from: http://www.ijem.in/text.asp?2014/18/2/246/129124

Sir,

We read with great interest the editorial on vitamin D deficiency (VDD) by Garg and colleagues. [1] It is apparent on biochemical analysis that subclinical VDD is a rapidly increasing global problem and needs urgent attention, as vitamin D has a major role in immune modulation, and VDD is associated with several communicable and noncommunicable diseases. [2],[3] The editorial is timely, as more and more Indians are getting their vitamin D levels tested and are finding that they have VDD. There are no clear evidence-based guidelines regarding the long-term management of such incidentally detected VDD. Differentiating a clinically significant VDD from an incidental biochemical finding is a major clinical challenge. Although the editorial has attempted to provide some guidelines, clinical recommendations must be based on high quality studies in the present era of evidence-based guidelines.

We wish to draw the attention of your readers to some issues related to simultaneous testing of 25-hydroxyvitamin D (25OHD) with parathyroid hormone (PTH) levels. First, the editorial is rather silent on the important question, namely measuring 25OHD in place of 1,25-dihydroxyvitamin D (1,25-DOHD, the functional hormone). Measurement of 25OHD as a biomarker of VDD is better than measuring 1,25-DHOD in day-to-day clinical practice because the former has a longer half-life and is the principal circulating form in blood. [3] 1,25-DHOD can be normal or elevated in VDD patients and is not truly indicative of vitamin D status. [3] Second, the authors have recommended measuring PTH along with 25OHD. Measuring PTH in a clinical laboratory is challenging: PTH circulates in blood as biologically active hormone and also as several inactive peptides. Currently, assays are not specific for biologically active PTH and can detect the inactive fragments as well. [4] Third, the set point of PTH secretion in response to serum calcium varies among individuals and is the result of a complex interaction of factors including age, gender, genetics, renal function, mobility level, calcium intake, and phosphate and magnesium status, which makes selection of a single inflection point challenging at best. [5] Last but not the least, the association of VDD in various disease states are modified by vitamin D receptor gene polymorphisms. [6]

Fixing a clinically relevant cut-off value for the trophic and the target hormones needs rigorous testing in real-life clinical situations, with adequate sample sizes and across age-groups. Use of such a combination testing in acute illness, chronic illness, and other comorbid conditions (e.g. diabetes) will require further analysis before being accepted into routine practice.

We wish to reiterate that 25OHD analysis is currently the best screening test available for VDD. Screening is just the beginning of a triage. If screening is indicative of VDD, a clinical pathway can be followed. In the current conundrum of inaccuracy and imprecision of the assays, absence of validated PTH reference material, unstandardized cut-offs, [4] and the multifactorial nature of bone metabolism, [2] a cointerpretation of PTH and 25OHD could result in net harm. It will also cause financial loss to the patients or their caregivers.

 
   References Top

1.Garg MK, Kalra S, Mahalle N. Defining vitamin D deficiency, using surrogate markers. Indian J Endocrinol Metab 2013;17:784-6.  Back to cited text no. 1
    
2.Norman AW. From vitamin D to hormone D: Fundamentals of the vitamin D endocrine system essential for good health. Am J Clin Nutr 2008;88:491S-9.  Back to cited text no. 2
    
3.Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: An endocrine society clinical practice guideline. J Clin Endocrinol Metab 2011;96:1911-30.  Back to cited text no. 3
    
4.Risteli J, Winter WE, Kleerekoper M, Risteli L. Bone and mineral metabolism. In: Burtis CA, Ashwood ER, Bruns DE, editors. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 5 th ed. Philadelphia: Saunders; 2012. p. 1733-801.  Back to cited text no. 4
    
5.Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Guidelines for preventing and treating vitamin D deficiency and insufficiency revisited. J Clin Endocrinol Metab 2012;97:1153-8.  Back to cited text no. 5
    
6.Vélayoudom-Céphise FL, Larifla L, Donnet JP, Maimaitiming S, Deloumeaux J, Blanchet A, et al. Vitamin D deficiency, vitamin D receptor gene polymorphisms and cardiovascular risk factors in Caribbean patients with type 2 diabetes. Diabetes Metab 2011;37:540-5.  Back to cited text no. 6
    



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