Transferrin

When elevated (>3.6 g/L) -- indicates iron deficiency:

Supplements:

• Iron Bisglycinate -- 25-50mg elemental iron/day (better absorbed, fewer GI side effects than ferrous sulfate)
• Vitamin C -- 500mg taken with iron to enhance absorption
• Take iron on empty stomach or with Vitamin C; avoid calcium, coffee, and tea within 2 hours (inhibit absorption)

Context for athletes:

• Elevated transferrin is the body's response to low iron stores -- it upregulates transport capacity to maximise iron delivery
• Common in AAS users who donate blood regularly to manage high haematocrit
• Confirm with low ferritin and low transferrin saturation
• Recheck iron studies 6-8 weeks after starting supplementation

When low (<2.0 g/L) -- possible chronic disease or inflammation:

• Low transferrin with low iron but normal/high ferritin suggests anaemia of chronic disease (not true iron deficiency)
• Investigate underlying inflammation (check CRP, ESR)
• Iron supplementation is NOT helpful in anaemia of chronic disease -- treat the underlying cause
• Liver disease can also reduce transferrin production

References:

• Camaschella, C. (2015). Iron-deficiency anemia. New England Journal of Medicine, 372(19), 1832-1843. DOI: 10.1056/NEJMra1401038