Iron

Some laboratories use 11 to 28 or 10 to 28 umol/L; it is highest in the morning and swings widely through the day and after meals; use the range your lab printed.

Serum iron is the amount of iron travelling through the blood at that moment, bound to its carrier protein transferrin. It is not a measure of the body's iron stores; ferritin does that. Because it changes hour by hour and with food, it is read as part of a set of iron studies rather than on its own.

Doctors request it as part of iron studies, mainly to calculate the transferrin saturation, when looking into anaemia, suspected iron overload, or the cause of a raised ferritin. It is rarely useful on its own.

• A recent meal or iron tablet, for a few hours
• Iron overload, including haemochromatosis
• Liver disease
• Conditions where red cells are broken down early
• Oestrogen-containing medicines
• Low vitamin B12 or folate, because iron is not being used

• Low iron stores
• Inflammation or infection, which locks iron away in the tissues
• Later in the day, as a daily rhythm
• Long-term kidney disease
• Heavy periods and pregnancy
• Some cancers

• It swings through the day and after meals more than almost any other routine test; a morning fasting value is the most stable
• An iron tablet taken within the last day raises it considerably
• A recent infection lowers it
• A haemolysed sample reads a little high

Best taken in the morning, fasting, with no iron tablets for 24 hours beforehand. Always read with transferrin or TIBC and ferritin.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.