Transferrin

Iron cannot travel loose through your blood; free iron is reactive and damages tissue. So your body has a carrier: transferrin, a protein from your liver that can grab two iron atoms at once and deliver them where they are needed, above all in the bone marrow that makes red blood cells from them. The transferrin value is the number of taxis on the road, whether they are occupied or not. How many taxis run, your liver decides on the basis of how much iron there is. If iron is scarce, the liver makes more transferrin, to pick up every atom the gut delivers straight away. If there is enough or too much, less. That makes transferrin move opposite to ferritin: in an iron deficiency the store is empty and the transferrin high. Two things cut across that pattern. With an inflammation the liver makes less transferrin, independently of the iron, and with a protein deficiency or a sick liver too. And oestrogen, from the pill or in pregnancy, makes the liver produce more transferrin without there being a deficiency. Your report shows transferrin in g/L. Normal is about 2.2 to 2.9 g/L for men and 2.5 to 3.2 g/L for women where the labs overlap. Serum iron divided by transferrin gives transferrin saturation, the share of taxis that is occupied.

Transferrin is the value that tells two kinds of anaemia apart that look alike but are treated in opposite ways. In a real iron deficiency your liver puts every taxi on the road: transferrin high, ferritin low, saturation low, and all three point the same way. In anaemia from a chronic inflammation or disease the picture is reversed: transferrin low or normal, ferritin high, and the iron sits in the store not because it has run out but because the body locks it away. In the first case iron helps; in the second iron does not help and tackling the inflammation does. Transferrin makes that distinction without further investigation. The second reason is diet. Transferrin is a protein the liver makes afresh every day, and with too little protein in the diet, on a strict diet or in a period of eating little it falls within weeks. A low transferrin without inflammation and with a normal iron is therefore one of the first signs that you take in too little protein, earlier than albumin shows it. And transferrin belongs to recognising iron overload early. In haemochromatosis transferrin is low or normal while saturation comes out far above the band, because the few taxis are all full. That pattern stands out before ferritin rises and before there is damage.

A high transferrin means a body looking for iron. In order of how often it occurs: an iron deficiency, a pregnancy, and the contraceptive pill or other oestrogens. In an iron deficiency ferritin is low and so is saturation; in a pregnancy or on the pill transferrin is high while the store is fine, and then saturation looks lower than it is. A low transferrin means a liver making fewer taxis. In order: an inflammation or illness, a liver disease, a protein deficiency, and rarely iron overload. CRP tells it apart from inflammation, the liver values from a sick liver, and albumin and your eating pattern from a protein deficiency. A low transferrin with a saturation above 45% is the picture of overload. Always read transferrin beside ferritin, serum iron, transferrin saturation and CRP. Transferrin does not swing over the day; do mention it if you are pregnant or use the pill.