Guide to Hemoglobin

WRITTEN BY

The Levels Team

Updated: 05/22/2025|12 min read

Summary

Hemoglobin is the iron-containing protein in red blood cells that carries oxygen from your lungs to all your body's tissues. 

Why It Matters

Hemoglobin is your body's oxygen delivery system. Each hemoglobin molecule can carry four oxygen molecules, and your red blood cells are packed with hemoglobin---about 250 million molecules per cell. This makes hemoglobin critical for getting oxygen to every cell in your body.

As blood flows through your lungs, hemoglobin picks up oxygen. When your blood reaches tissues that need oxygen, hemoglobin releases it. This process happens constantly, with hemoglobin making the round trip between your lungs and tissues roughly every minute, though it can be faster during exercise or physical stress.

Hemoglobin also helps regulate your blood's pH balance and carries some carbon dioxide back to your lungs to be exhaled. 

Without enough functioning hemoglobin, your tissues can't get the oxygen they need, leading to fatigue and other symptoms. Too much hemoglobin, on the other hand, can make your blood too thick, increasing the risk of clots. Testing hemoglobin helps ensure you have the right amount for proper oxygen delivery throughout your body.

Associated Symptoms

Hemoglobin levels themselves are laboratory findings rather than medical conditions. However, abnormal levels may be associated with various health conditions, each with their own symptoms.

Common symptoms that may indicate conditions associated with low hemoglobin (anemia):

• Fatigue and weakness: Reduced oxygen delivery to tissues can impair energy production and muscle function
• Shortness of breath: Especially during physical activity, can occur as the body struggles to deliver sufficient oxygen
• Dizziness: Decreased oxygen supply to the brain can affect balance and coordination
• Pale skin: Reduced hemoglobin in small blood vessels may cause visible pallor, particularly noticeable in nail beds and mucous membranes
• Cold hands and feet: Can result from poor circulation and reduced oxygen delivery to extremitie
• Rapid heartbeat: May result from the heart pumping faster to compensate for reduced oxygen-carrying capacity

Common symptoms that may indicate conditions associated with high hemoglobin (polycythemia):

• Headaches: Can be related to increased blood viscosity and altered cerebral blood flow
• Visual disturbances: Reduced blood flow through retinal vessels may be due to increased blood thickness
• Facial flushing or ruddy complexion: May result from increased red cell concentration in facial blood vessels
• Itchy skin: Particularly after warm showers, may be related to histamine release
• Fatigue: Despite high oxygen-carrying capacity, thickened blood flows less efficiently

It's important to understand that many factors can cause these symptoms, and hemoglobin levels are just one piece of diagnostic information. The presence of symptoms alongside abnormal hemoglobin provides context for further investigation, but additional testing is typically needed to determine the underlying cause.

Clinical Ranges

Female:

• ≤18 Years: 11.5-15.3 g/dL
• >18 Years: 11.7-15.5 g/dL

Male:

• ≤18 Years: 12.0-16.9 g/dL
• >18 Years: 13.2-17.1 g/dL

Lifestyle Factors That Can Impact It

Factors that help increase hemoglobin include the following:

• Iron-rich foods provide building blocks for new hemoglobin.
• Vitamin C with meals enhances iron absorption for hemoglobin production.
• Adequate protein intake supports hemoglobin synthesis.
• Good sleep habits support blood cell production.
• Smoking will increase hemoglobin due to carbon monoxide exposure, which impairs oxygen delivery but stimulates erythropoiesis.
• Altitude increases hemoglobin due to chronic hypoxia
• Dehydration can concentrate hemoglobin, falsely elevating levels

Factors that can decrease hemoglobin include the following:

• Excessive endurance exercise can break down red blood cells.
• Chronic stress can impair red blood cell production.
• Poor nutritional intake lacking B12/Folate or vegetarian or vegan diets that are low in B12

Other Factors That Can Impact It

Medical Conditions

• Iron deficiency: decreases hemoglobin by limiting production
• Upper GI bleed: can decrease hemoglobin
• Kidney disease: lowers hemoglobin by reducing erythropoietin (EPO), a hormone that helps produce red blood cells 
• Bone marrow disorders: may increase or decrease production of red blood cells, depending on underlying condition
• Chronic inflammation: interferes with iron usage and hemoglobin production
• Lung disease: can increase hemoglobin to compensate for low oxygen

Medications

• Iron supplements: increase hemoglobin production
• EPO medications: stimulate red blood cell production and hemoglobin
• Chemotherapy: can decrease hemoglobin production
• NSAIDs: may cause small blood losses, lowering hemoglobin
• Some antibiotics: can affect red blood cell production
• Blood pressure medications: may affect blood cell production
• Chemotherapy can lower hemoglobin

Genetic Factors

• Thalassemia: lowers hemoglobin production
• Sickle cell trait: changes hemoglobin structure 
• Hereditary spherocytosis: affects red blood cell stability
• G6PD deficiency: can cause hemoglobin breakdown
• EPO receptor variants: affect red blood cell production
• Iron metabolism genes: influence hemoglobin synthesis

Environmental Factors

• Altitude: higher altitude increases hemoglobin production
• Lead exposure: interferes with hemoglobin synthesis
• Carbon monoxide exposure: blocks hemoglobin's oxygen-carrying ability
• Air pollution: may affect oxygen transport
• Radiation exposure: can decrease blood cell production

Testing Accuracy and Stability

Hemoglobin testing is generally reliable, but a few factors like hydration, exercise, and pregnancy can affect levels and accuracy.

Factors That Can Affect Your Test Results

• Dehydration falsely increases levels.
• Recent exercise can temporarily increase levels.
• Levels are naturally lower during pregnancy.
• Regular blood donations can lower levels through blood loss.

How it Relates to Other Markers

Understanding how other markers influence hemoglobin helps provide context for your results and guide treatment decisions. Many markers work together to affect your body's ability to produce and maintain healthy hemoglobin levels.

Key related markers include:

• Iron studies: Low iron directly reduces hemoglobin production because iron is a building block of hemoglobin molecules.
• Ferritin: This test shows iron storage available for hemoglobin production. Low ferritin means you don't have enough iron reserves to make adequate hemoglobin.
• Red blood cell count: This marker rises and falls with hemoglobin since each red blood cell contains hemoglobin. Changes in one usually mean changes in the other.
• Hematocrit: This test also increases or decreases with hemoglobin because it measures the percentage of blood volume made up by red blood cells, which contain hemoglobin.
• B12 and folate: These vitamins are necessary for red blood cell production. A deficiency in one or both can reduce your body's ability to make new red blood cells and hemoglobin.
• Kidney function: Your kidneys produce erythropoietin (EPO), which stimulates red blood cell production. Poor kidney function means less EPO and lower hemoglobin.
• Inflammatory markers: High inflammation interferes with iron use and can reduce hemoglobin production by making iron less available.
• Reticulocyte count: This marker shows how many new red blood cells your body is making. High counts may suggest your body is trying to increase hemoglobin, while low counts may suggest reduced production.

Follow-up Considerations

If your hemoglobin level is out of range, your provider may recommend iron supplements, diet changes, lifestyle modifications, or other treatments. They may retest your level to see how it responds to any interventions, and may recommend other tests. You should always speak to your doctor if you have medical questions or before making medical decisions.

When Re-Testing May be Appropriate

• Normal levels: Annually
• Frequency of re-testing is typically based on the underlying condition for what's causing the anemia
• Pregnancy: Typically at first prenatal visit and again between 24 and 28 weeks

Additional Testing or Monitoring Your Doctor May Consider

• Genetic testing if indicated
• Bone marrow evaluation if severe

When Additional Care May be Warranted

• Blood transfusions are usually widely recommended when the hemoglobin is less than 7
• Severe anemia (Hgb < 8 g/dL)
• Very high levels (> 20 g/dL)
• Rapid changes in levels
• New symptoms
• No response to treatment
• Unexplained changes

Bibliography