A1c and anemia

Iron deficiency: the A1c reads high

A 2015 systematic review in Diabetologia pooled 12 studies of nonpregnant adults without known diabetes. Most looked at iron-deficiency anemia. In general, iron deficiency with or without anemia led to higher A1c values than in people without it, with no matching rise in glucose (English 2015). The authors concluded that iron deficiency is likely to cause a spurious increase in A1c, which can cause confusion when A1c is used to diagnose diabetes (English 2015). NIDDK also notes that a falsely high A1c can occur in people who are very low in iron (NIDDK).

This matters most near a cut point. Someone with low iron and an A1c of 5.8% or 6.6% could be classed as having prediabetes or diabetes by A1c, while their glucose tests are normal. That is one of the reasons behind A1c high but glucose normal.

Other anemias: the A1c can read low

When red blood cells are destroyed or lost faster than usual, they have less time to collect glucose, and the ADA notes this usually lowers A1c (ADA Standards 2026, sec. 2). Hemolysis and recent blood loss are examples (ADA Standards 2026, sec. 2). The 2015 review found more limited data, but a possible decrease in A1c with anemias not caused by iron deficiency (English 2015). A low A1c in these cases can hide high blood sugar.

What doctors use instead

• Plasma glucose tests. In conditions that may alter red blood cell turnover, the ADA says plasma glucose criteria should be used to diagnose diabetes: a fasting plasma glucose or a 2-hour glucose tolerance test (ADA Standards 2026, sec. 2).
• Looking for the cause of a mismatch. When A1c and blood glucose disagree in a large and consistent way, the ADA recommends looking for interference or a problem with either test (ADA Standards 2026, sec. 2).
• Checking the blood count. MedlinePlus lists anemia among the conditions in which an A1c may be incorrect (MedlinePlus), which is why a blood count and iron tests are often part of the picture.

The ADA does not give a fixed amount by which A1c moves per gram of hemoglobin, and the 2015 review says more evidence is needed on which types and degrees of anemia matter (English 2015). So there is no reliable way to "correct" an A1c at home.

Frequently asked questions

Does anemia make A1c high or low?

It depends on the type. Iron deficiency, with or without anemia, tends to raise A1c without any rise in glucose. Anemias that make red blood cells turn over faster, such as hemolysis or recent blood loss, usually lower it.

Can iron deficiency cause a high A1c?

Yes. A systematic review found that iron deficiency, with or without anemia, led to higher A1c values than in people without it, with no rise in glucose. The ADA also lists iron-deficiency anemia as a cause of a falsely high A1c.

Can I be diagnosed with diabetes using A1c if I have anemia?

The ADA says A1c may not be a suitable diagnostic test in people with anemia, and that plasma glucose criteria should be used when red blood cell turnover may be altered.

What should I ask my doctor?

Whether your blood count and iron levels have been checked, whether they could be affecting your A1c, and whether a fasting glucose or glucose tolerance test would give a clearer answer.