Why Am I So Tired When My Blood Work Is Normal? What Standard Testing Misses — What “in range” actually means

The reference range for most labs is statistical, not biological. It represents the values that fall within two standard deviations of the population mean. The population from which the range was derived is not selected for health. It is selected for being whoever showed up at the lab. This produces several distortions. The reference range for TSH was developed from a population that included subclinical hypothyroid patients. The reference range for ferritin includes patients with chronic low-grade inflammation that elevates ferritin spuriously. The reference range for vitamin D was set against a population that is broadly deficient. The reference range for B12 includes elderly patients with functional B12 deficiency due to absorption issues. In each case, the reference range tells you about the population, not about your specific physiological need. The clinically useful concept is the optimal range, which differs from the reference range substantially for many markers. A TSH of 2.5 may be reported as normal but is associated with worse symptoms than a TSH of 1.5 in many patients. A ferritin of 30 is within reference range but is associated with worse fatigue than a ferritin of 80 in many women. A vitamin D of 32 is within reference range but is associated with worse immune function than a vitamin D of 50. The &ldquo;in range&rdquo; reading on the lab report is often what the