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The finger prick test doesn’t test iron levels –and other things you should know before donating blood

The finger prick test doesn’t test iron levels –and other things you should know before donating blood

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South Africans are encouraged to donate blood as the festive season approaches but how much do you know about the donation process before you donate blood?

As most of us know, donors are encouraged to eat a filling and healthy breakfast and answer the questionnaire to the best of your ability and honestly, before donating blood. Clinic staff then do a finger prick test to check haemoglobin levels, not iron levels.

That is right, my fellow South Africans, your whole life was a lie. However, you can be forgiven for thinking the finger-prick does test iron levels as clinic staff and numerous websites mention “iron levels” when referring to the finger prick test.

Dr Caroline Hilton, who manages the medical department at the Western Cape Blood Service, broke down the difference.

“In a nutshell, the finger prick test that is performed prior to your donation is actually a measure of your haemoglobin level, which staff often incorrectly refer to as ‘iron’. The haemoglobin measurement ensures that you have sufficient red blood cells to donate without becoming anaemic,” said Hilton. It is worth noting that haemoglobin levels are tested in g/dl whereas ferritin levels are tested in ug/l.

Hilton said: “The result you would receive by SMS is your ferritin value (if it is very low or very high), which is completely different, performed by a machine at our laboratories after you have donated, and is a measurement of your stored iron levels.”

So think of haemoglobin as a car. This car (which is the protein in our red blood cells) carries its favourite passenger, which is oxygen in the blood.

Your haemoglobin level is tested to make sure you have sufficient red cells in your body to spare for the donation.

Hilton said haemoglobin contains iron, but is not necessarily a reflection of all the iron you have as it is used and stored in other parts of the body besides the red blood cells. Ferritin refers to the amount of iron stored in the body, which can be measured by a blood test.

So what are the requirements and level cut-offs?

The minimum haemoglobin (finger-prick) cut-off for women is 12.5 g/dl and 13.5 g/dl for men. With regards to ferritin levels, donors are notified if their ferritin levels are below 15ug/l or above 500ug/l.

When someone’s ferritin levels are low, donors are advised to inform their doctor that they are iron deficient so that this can be investigated.

“While regular blood donation can be a cause of low iron stores, there could be a more sinister cause of their iron deficiency. They are advised to take a break from donating blood as each donation depletes the iron stores further,” said Hilton, adding that iron tablets are offered at the clinics in a bid to replace the iron lost in the donor’s blood donation.

What should you know before donating blood?

Aside from the usual “eat a sufficient breakfast”, there are two things to bear in mind before donating blood. One of them is the questionnaire you might have skimmed through.

“The questionnaire should be answered as truthfully as possible as each question is there for a reason. Donors should realise that there is risk of infection being passed from their bloodstream to the patient,” Hilton said.

Hilton noted that blood donation can steadily deplete your stored iron levels. This results in iron deficiency. Low iron stores can result in lethargy and fatigue.

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