RBC blood test: what a high or low red blood cell count means

What the RBC count measures

Red blood cells (erythrocytes) carry oxygen from your lungs to your body using hemoglobin. The RBC count is reported in millions of cells per microliter.

It is read with hemoglobin, hematocrit and the red cell indices such as MCV, which show cell size. A count can be normal while the cells themselves are too small or too large, so the indices matter. See the CBC guide and the complete blood count lab guide.

What a low RBC count can mean

• Anemia from low nutrients: iron, vitamin B12 or overall poor nutrition. Check iron with ferritin.
• Blood loss, from an injury or other bleeding.
• Kidney disease or kidney failure.
• Pregnancy.
• Alcohol use disorder.
• Bone marrow conditions and cancers, such as leukemia or multiple myeloma.

Symptoms of a low count include tiredness or weakness, shortness of breath, headache, dizziness, pale skin and an irregular heartbeat.

What a high RBC count can mean

A high count is also called erythrocytosis or polycythemia. It thickens the blood and can raise clotting risk. Causes:

• Dehydration, which concentrates the blood without adding cells
• Smoking and carbon monoxide exposure
• Living at high altitude
• Sleep apnea and lung disease such as COPD or lung scarring
• Heart disease that lowers blood oxygen
• Testosterone and anabolic steroids, or EPO used to boost performance; see high hematocrit on TRT
• Less common: kidney or liver tumors, and polycythemia vera, a bone marrow condition that makes too many red cells

Symptoms, when present, include headache, dizziness, blurry vision, itchy skin and nosebleeds. Many people have none.

Gabriel's optimal ranges

Typical lab ranges differ by sex and lab; one common set is about 4.1 to 5.8 million per microliter for men and 3.8 to 5.1 for women. Gabriel's optimal ranges are narrower: 4.8 to 5.5 for men and 4.3 to 4.8 for women. These are targets to discuss with your clinician, and the evidence behind them is limited, especially for women.

What to do with an abnormal result

1. Read it with hemoglobin, hematocrit and MCV. Together they show whether you are anemic and point toward the type.
2. For a low count, ask about ferritin and an iron panel, vitamin B12, folate and kidney function.
3. For a high count, think about hydration on the day of the draw, smoking, altitude, snoring or daytime sleepiness, and any testosterone use. Ask whether a repeat test or an EPO level makes sense.
4. Retest after a change. Red cells turn over slowly, so give a fix time before rechecking.
5. If you have a report in hand, you can upload it to Gabriel for a plain-words read of every marker, then take your questions to your clinician.

Seek care right away for chest pain, fainting, severe shortness of breath, black or bloody stools, or signs of a stroke such as face drooping or sudden weakness. See a clinician soon for a high RBC with headaches or vision changes, or a low RBC with ongoing tiredness or heavy bleeding.