Evidence check: Transferrin in the context of fatigue

Transferrin is a blood protein that transports iron. Low transferrin saturation can indicate iron deficiency, a well-known cause of fatigue. However, transferrin alone is not a direct marker for fatigue – clinical assessment requires additional measures like ferritin, hemoglobin, and inflammatory markers. Studies show a moderate association between low transferrin saturation and fatigue in iron-deficient individuals, especially in women of reproductive age. Yet the evidence is not strong enough to recommend transferrin as a standalone predictor. Many other factors (sleep, stress, thyroid, vitamin deficiencies) can cause fatigue. Measuring transferrin is useful as part of a comprehensive iron panel, but not as an isolated test. Caution: normal transferrin does not rule out iron deficiency, and elevated levels can occur with inflammation. Overall, moderate evidence for the utility of transferrin in fatigue evaluation.