A high hemoglobin count indicates an above-normal level of the iron-containing protein in red blood cells. Hemoglobin (often abbreviated as Hb or Hgb) is the oxygen-carrying component of red blood cells.

Hemoglobin, which gives red blood cells their color, helps carry oxygen from the lungs to the rest of the body and carbon dioxide back to the lungs to be exhaled.

The threshold for a high hemoglobin count differs slightly from one medical practice to another. It's generally defined as more than 16.6 grams (g) of hemoglobin per deciliter (dL) of blood for men and 15 g/dL for women. In children, the definition of a high hemoglobin count varies with age and sex. Hemoglobin count may also vary due to time of day, how well-hydrated you are and altitude.

A high hemoglobin count occurs most commonly when your body requires an increased oxygen-carrying capacity, usually because:

• You smoke
• You live at a high altitude and your red blood cell production naturally increases to compensate for the lower oxygen supply there

High hemoglobin count occurs less commonly because:

• Your red blood cell production increases to make up for chronically low blood oxygen levels due to poor heart or lung function.
• Your bone marrow produces too many red blood cells.
• You've taken drugs or hormones, most commonly erythropoietin (EPO), that stimulate red blood cell production. You're not likely to get a high hemoglobin count from EPO given to you for chronic kidney disease. But EPO doping — getting injections to enhance athletic performance — can cause a high hemoglobin count.

If you have a high hemoglobin count without other abnormalities, it's unlikely to indicate a related serious condition. Conditions that can cause a high hemoglobin count include:

• Congenital heart disease in adults
• COPD (chronic obstructive pulmonary disease) — the blanket term for a group of diseases that block airflow from the lungs — including emphysema.
• Dehydration (when the body doesn't have enough water and other fluids to work as it should)
• Emphysema
• Heart failure
• Kidney cancer
• Liver cancer
• Polycythemia vera

A high hemoglobin count is usually found from tests your doctor has ordered to diagnose another condition. Your doctor is likely to order other tests to help determine the cause of your high hemoglobin count.