Hemoglobin blood test: what low or high hemoglobin means

What hemoglobin measures

Hemoglobin picks up oxygen in your lungs and delivers it to the rest of your body. The test is almost always part of a complete blood count (CBC), reported in grams per deciliter (g/dL).

It is read with hematocrit (the share of your blood made of red cells), the red blood cell count and the red cell indices such as MCV. It is a different test from hemoglobin A1C, which tracks average blood sugar; see the A1C test.

Normal and anemia ranges by sex

There is no single cutoff. Each lab prints its own reference range, and age, altitude and pregnancy shift what is expected. These are typical adult lab ranges; your report's range is the one that applies to you.

A result below your lab's range is generally read as anemia. Gabriel's optimal bands are narrower (14 to 16 g/dL for men, 13.5 to 14.5 g/dL for women). A woman a little under 13.5 is not anemic; it is a prompt to check ferritin and menstrual blood loss.

What low hemoglobin can mean

• Low iron. The most common nutritional cause. Hemoglobin falls late, so ferritin is the better early check; see ferritin levels.
• Blood loss. Heavy periods, an injury, or slow bleeding in the gut.
• Low vitamin B12 or folate. Both are needed to make red cells; see the vitamin B12 blood test.
• Chronic illness or kidney disease. Long-term inflammation and kidney disease can slow red cell production.
• Inherited conditions such as thalassemia, and destruction of red cells (hemolysis).
• Pregnancy. Blood volume rises, so hemoglobin normally dips.

Common symptoms of anemia are tiredness, weakness, dizziness, cold hands and feet, headache and shortness of breath with exertion. Many people with mild anemia feel fine.

What high hemoglobin can mean

High hemoglobin is most often the body's response to long-term low oxygen. Common causes:

• Smoking.
• Dehydration, which concentrates the blood. A repeat test after rehydrating often comes back lower.
• Living at high altitude. Levels rise for several weeks after moving higher.
• Sleep apnea, lung disease or heart disease.
• Certain medicines. Bring your full medication list. If you use testosterone, see high hematocrit on TRT.
• Less common: polycythemia vera, a bone marrow condition, and some kidney tumors.

What to do with an abnormal result

1. Read it with the rest of the CBC. Hematocrit, MCV and RDW help narrow down the cause.
2. Ask about the follow-up tests that fit. For low hemoglobin that usually means ferritin, an iron panel, B12 and folate. For high hemoglobin, a repeat test when well hydrated, and questions about smoking, sleep and medications.
3. Retest after a change. Hemoglobin moves slowly, so ask your clinician when a recheck will be meaningful.

Get care promptly if low hemoglobin comes with chest pain, shortness of breath at rest, fainting, a racing heart, or black, tarry or bloody stools. Very high hemoglobin with a severe headache, vision changes or one-sided weakness needs emergency care.