… When testing with ZRT, you will receive a result that is reflective of your total 25-Hydroxy Vitamin D status (vitamin D2 plus Vitamin D3) in blood. This is the storage form of vitamin D, which is converted by the kidneys to the biologically active form, 1,25-dihydroxycholecalciferol. …
Reference Range
The reference range, a term often used in conjunction with laboratory testing, is a set of values that include the upper and lower limits of a lab test based on a group of otherwise healthy individuals. For a laboratory to determine the appropriate reference range for their testing population, often hundreds to thousands of normal, healthy patients are tested. To date, ZRT has tested over 60,000 patients to assess their vitamin D levels. When looking at the patient results, we determined that the majority of patients tested have total vitamin D levels between 20 and 80 ng/mL; that is, 86% of patients tested fall within this range. Based on years of patient testing and data analysis, we have updated our laboratory report reference range to reflect that values between 20-80 ng/mL are representative of a normal patient population.
Normal versus Optimal
This raises the issue: is normal the same thing as optimal? Not necessarily. The Vitamin D Council places the ideal level between 40 and 80 ng/mL with levels below 20 ng/mL as deficient. The Endocrine Society has a Clinical Practice Guideline on the evaluation, treatment, and prevention of vitamin D deficiency. This guideline recommends a minimum vitamin D level of 20 ng/mL, but to guarantee sufficiency they recommend between 30 and 50 ng/mL for both children and adults. In contrast, the Vitamin D Council states that even levels between 30 and 40 ng/mL are still not quite sufficient. On the other end of the spectrum, results that fall between 80 and 100 ng/mL are not achievable naturally; that is, they are only reached with some form of vitamin D supplementation. So, while they are not harmful levels, they are instead reflective of supplementation and therefore not what would be detected in a “normal” patient population.
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