DEAR DOCTOR K: I’m a 31-year-old woman, and I try to donate blood every couple of months, but the last time I tried, I was turned away because my hemoglobin was too low. What does that mean? And what can I do about it?

DEAR READER: That’s terrific that you are a regular blood donor. The American Red Cross says that one pint of blood – roughly the amount collected during a donation – can treat an average of three people who need blood.

Before every blood donation, you get a mini physical. A technician checks your temperature, blood pressure, pulse and hemoglobin. Hemoglobin is the part of red blood cells that carries oxygen throughout the body. It is made up of iron and protein.

Your hemoglobin must be at least 12.5 grams per deciliter in order to donate blood. Since in giving a pint of blood you give away both hemoglobin and iron, you are not allowed to give a blood donation if your hemoglobin level already is low.

It may be that your hemoglobin level was low because your iron levels are low. Women who are menstruating can develop low iron and low hemoglobin levels because they lose blood every month. You should have your doctor check your hemoglobin and your iron levels. If they are low, your doctor may perform further tests to find out why. You may also have related questions: Will I be turned away again in the future? Following a blood donation, when I lose hemoglobin and iron, what can I do to build my blood back up quickly?

A recent study suggests one way you can rebuild your hemoglobin faster after donating blood. The study found that people who took iron pills had their hemoglobin levels recover faster than those who did not take iron pills.

If you donate blood often, ask your doctor about taking an iron supplement. One standard 325 milligram ferrous gluconate pill each day should be enough.

Don’t take iron with milk, antacids or calcium, which block iron absorption. Taking the pill with orange juice or 250 milligrams of vitamin C can help the body better absorb the iron.