A hemoglobin test measures the amount of hemoglobin, an oxygen-carrying protein, in your blood. The healthy range is 13.2 to 16.6 grams per deciliter (g/dL) for men and 11.6 to 15 g/dL for women. Results outside these ranges can signal anemia, blood disorders, chronic diseases, or other conditions affecting your red blood cells.
What Hemoglobin Does in Your Body
Hemoglobin is a protein packed inside red blood cells. It contains iron, which binds to oxygen in your lungs and carries it through your bloodstream to every tissue in your body. When red blood cells reach tissues that need oxygen, hemoglobin releases it so your cells can produce energy. The iron in hemoglobin is also what makes blood red.
Red blood cells are built for this job. They’re small and flexible enough to squeeze through the narrowest blood vessels, and their disc-like shape maximizes the surface area available to absorb oxygen. When hemoglobin levels drop too low, your body can’t deliver enough oxygen to keep up with demand. When levels climb too high, blood can become thick and sluggish.
Why Your Doctor Orders This Test
A hemoglobin test is one of the most common blood tests in medicine. It’s often included in a routine complete blood count (CBC), so you may have had one without specifically requesting it. Beyond routine screening, doctors order it when specific concerns arise:
- Symptoms of anemia: weakness, dizziness, fatigue, pale skin, or cold hands and feet
- Family history: inherited blood disorders like sickle cell disease or thalassemia
- Nutritional gaps: a diet low in iron, folate, or vitamin B12
- Chronic infections or inflammatory conditions
- Significant blood loss: from surgery, injury, or heavy menstrual periods
It’s also used to monitor treatment. If you’ve been diagnosed with anemia or a condition that affects red blood cells, repeat hemoglobin tests track whether your levels are improving.
What Low Hemoglobin Reveals
A hemoglobin level below the normal range points to anemia, but that’s a broad category with many possible causes. The underlying problem falls into one of three patterns: your body is making fewer red blood cells than normal, destroying them faster than it can replace them, or losing blood.
Iron deficiency anemia is the most common culprit worldwide. It happens when your body doesn’t have enough iron to produce adequate hemoglobin. Heavy menstrual bleeding, pregnancy, and diets low in iron-rich foods are frequent triggers. Vitamin deficiency anemia works similarly, but the missing nutrients are folate or vitamin B12 instead of iron.
Chronic diseases can also suppress red blood cell production. Kidney disease is a major one because the kidneys produce a hormone that signals your bone marrow to make red blood cells. When kidneys aren’t functioning well, that signal weakens. Other conditions linked to low hemoglobin include hypothyroidism, inflammatory bowel disease, rheumatoid arthritis, cirrhosis, and certain cancers like leukemia and lymphoma. Some medications, particularly chemotherapy drugs, can lower hemoglobin as a side effect.
In inherited conditions like sickle cell disease and thalassemia, the hemoglobin molecule itself is abnormal. Sickle cell disease causes red blood cells to become rigid and crescent-shaped, making them break down faster than healthy cells. Thalassemia reduces the amount of hemoglobin each red blood cell can carry. An enlarged spleen can also destroy red blood cells prematurely, pulling hemoglobin levels down.
Blood loss is the most straightforward cause. Bleeding in the digestive tract from ulcers, polyps, or hemorrhoids can be slow enough that you don’t notice it, yet persistent enough to gradually drain your hemoglobin over weeks or months.
What High Hemoglobin Reveals
Elevated hemoglobin is less common but still clinically significant. Sometimes it’s a simple fluid issue: dehydration reduces the liquid portion of your blood, making your red blood cell concentration appear higher than it actually is. Once you rehydrate, levels return to normal.
Living at high altitude naturally raises hemoglobin. With less oxygen in the air, your body compensates by producing more red blood cells. Smoking has a similar effect because carbon monoxide from cigarettes occupies space on hemoglobin that would normally carry oxygen, prompting your body to make extra red blood cells to compensate.
More serious causes involve the bone marrow overproducing red blood cells. In primary erythrocytosis (including polycythemia vera), a genetic defect in bone marrow stem cells drives excessive red blood cell production. Secondary erythrocytosis occurs when something outside the bone marrow, like chronic lung disease or sleep apnea, triggers the overproduction by keeping oxygen levels chronically low. Thick, concentrated blood increases the risk of clots, which is why persistently high hemoglobin needs investigation.
Factors That Shift Your Results
Your age, sex, and where you live all influence what’s normal for you. The CDC has confirmed that hemoglobin readings need to be adjusted for altitude and smoking status to avoid misdiagnosis. Without these adjustments, a person living at sea level might be incorrectly flagged as anemic, while someone at high altitude with genuinely low levels could be missed. Current guidelines may slightly underadjust for light smokers and overadjust for people at very high altitudes.
Pregnancy also lowers hemoglobin. Blood volume expands significantly during pregnancy, diluting the concentration of red blood cells even when the total number is adequate. That’s why pregnant women have different reference ranges than the general population.
Hemoglobin vs. Hemoglobin A1c
These two tests share a name but measure completely different things. A standard hemoglobin test counts how much hemoglobin protein is in your blood, reflecting your red blood cell health. A hemoglobin A1c test measures the percentage of hemoglobin molecules that have glucose (blood sugar) stuck to them, giving a snapshot of your average blood sugar over the past two to three months.
Glucose in your bloodstream naturally attaches to hemoglobin. The higher your blood sugar runs over time, the greater the percentage of glucose-coated hemoglobin. That’s why A1c is used to diagnose and monitor diabetes, while a standard hemoglobin test is used to evaluate anemia and blood disorders. If your doctor orders “a hemoglobin test” without mentioning A1c, they’re checking your red blood cell protein levels, not your blood sugar.
What the Test Involves
A hemoglobin test requires a simple blood draw, typically from a vein in your arm. No fasting is required unless other tests are being run at the same time. Results are usually available within a day. The number you’ll see on your results is measured in grams per deciliter (g/dL), and your lab report will list the reference range right next to your result so you can see where you fall.
A single hemoglobin reading is a starting point, not a diagnosis. If your level comes back outside the normal range, your doctor will look at other values from the same blood draw (like red blood cell size and count) and consider your symptoms, medical history, and lifestyle before determining the cause and whether further testing is needed.