Iron (Serum Iron)

Serum iron measures the amount of iron currently circulating in the bloodstream, bound to transferrin. It is a single snapshot in time and varies significantly by time of day (highest in the morning, lowest at night) and by recent meals. Serum iron is one of four results on the standard Australian iron studies panel — alongside ferritin (iron stores), transferrin / TIBC, and transferrin saturation — and is most useful when interpreted as part of the full panel rather than in isolation.

Iron is essential for haemoglobin synthesis, oxygen transport, energy production, immune function and cognitive performance. Iron studies are one of the most commonly ordered blood tests in Australia, used to investigate fatigue, hair loss, restless legs, exercise intolerance, heavy menstrual bleeding, vegetarian/vegan diets and unexplained anaemia. They are also used to screen for haemochromatosis (iron overload) — a common inherited condition affecting roughly 1 in 200 Australians of Northern European descent.

High serum iron often reflects haemochromatosis (HFE gene mutation), iron supplementation taken on the morning of the blood draw, frequent blood transfusions, or acute liver injury releasing stored iron. Persistently high iron with elevated transferrin saturation (>45%) and rising ferritin is the screening pattern for hereditary haemochromatosis and is followed up with HFE genetic testing in Australia. A single high serum iron in isolation is rarely meaningful — interpretation requires the full iron studies panel and ideally a repeat fasting morning sample without recent supplements.

Low serum iron is most commonly caused by iron-deficiency anaemia (inadequate dietary intake, heavy menstrual bleeding, pregnancy, gastrointestinal blood loss from ulcers, polyps, coeliac disease or colorectal cancer), anaemia of chronic disease (where iron is sequestered away from the bloodstream by inflammation), or chronic kidney disease. Pure low serum iron with normal ferritin is often non-significant — but low serum iron + low ferritin + high TIBC = classic iron deficiency. Low serum iron + low TIBC = anaemia of chronic disease. Vegan and vegetarian diets, gastric bypass, distance running and frequent blood donation are common Australian risk factors.

Iron studies are recommended annually for premenopausal women, vegans and vegetarians, distance athletes, frequent blood donors and anyone with metabolic risk factors for haemochromatosis. People with established iron deficiency should retest 4–6 weeks after starting oral iron, then every 3 months until ferritin is in the upper-normal range, then annually. People on TRT or with polycythaemia should monitor iron studies every 3–6 months because frequent therapeutic phlebotomy depletes iron.

Always interpreted alongside ferritin (the most important single iron marker), transferrin or TIBC, transferrin saturation, haemoglobin, MCV and MCH. The full panel is needed to distinguish iron deficiency from anaemia of chronic disease and from haemochromatosis.