High hemoglobin count

Date Updated: 02/15/2025

Definition

A high hemoglobin (Hb or Hgb) count is a blood test result. It means that the level of a key protein in red blood cells called hemoglobin is higher than is typical. Hemoglobin carries oxygen throughout the body. It also gives red blood cells their color.

Hemoglobin is measured in grams per deciliter (g/dL) of blood. What's considered a high hemoglobin count differs slightly from one lab to another. In general, a high hemoglobin count is more than 16.6 g/dL for men and more than 15 g/dL for women. In children, a high hemoglobin count varies with age and sex.

Other factors that can affect hemoglobin count include:

The time of day.
How hydrated you are.
How high above sea level you are.

Causes

Most often, a high hemoglobin count happens when the body needs more oxygen. The body may need more oxygen due to:

Smoking tobacco. This can lessen blood flow and cause less oxygen to reach the heart and lungs.
Living high above sea level. Oxygen levels in the air are lower at high altitudes.

Less often, a high hemoglobin count happens because:

The body creates more red blood cells to make up for low oxygen levels due to heart or lung conditions.
The bone marrow makes too many red blood cells.
Some medicines or hormones cause the body to make more red blood cells. For example, lab-made versions of the sex hormone testosterone are a treatment for some men with low testosterone. This treatment is called testosterone replacement therapy, and it can cause a high hemoglobin count as a side effect.

If you have a high hemoglobin count without other concerning test results, you likely don't have a serious underlying condition. But some health conditions can cause a high hemoglobin count, including:

Congenital heart disease in adults — one or more changes in the heart's structure that are present at birth.
COPD — a long-term lung disease that causes trouble with breathing.
Dehydration — when the body doesn't have enough water and other fluids to work as it should.
Emphysema — a lung condition that causes shortness of breath.
Heart failure — a condition in which the heart doesn't pump blood as well as it should.
Kidney cancer — cancer that starts in the kidneys.
Liver cancer — cancer that starts in the liver.
Polycythemia vera — a type of blood cancer.
Obstructive sleep apnea — the most common sleep-related breathing condition.

When to see a doctor

A very high hemoglobin count can lead to symptoms. Talk with your healthcare professional if you have symptoms such as:

Trouble with vision.
Dizziness.
Headache.
Slurred speech.

Keep in mind that these symptoms can happen for many different reasons. It's more common to find a high hemoglobin count during a routine blood test or a test checking for another condition. Your healthcare professional likely will do more tests to help figure out the cause of the high hemoglobin count.