A serum hemoglobin test measures the amount of free-floating hemoglobin in your blood serum. Serum is the liquid that is left over when the red blood cells and the clotting elements have been removed from your blood plasma. Hemoglobin is a type of oxygen-carrying protein found in your red blood cells.
Normally, all of the hemoglobin in your body is contained in your red blood cells. However, some conditions may cause some of the hemoglobin to be in your serum. This is called free hemoglobin. The serum hemoglobin test measures this free hemoglobin.
Doctors usually use this test to diagnose or monitor abnormal breakdown of red blood cells. If you have had a recent blood transfusion, this test can monitor for a transfusion reaction. Another cause might be hemolytic anemia. If you have this type of anemia, your red blood cells break down too quickly. This leads to higher-than-normal levels of free hemoglobin in your blood.
The test is sometimes called a blood hemoglobin test.
Your doctor may order a serum hemoglobin test if you are exhibiting symptoms of hemolytic anemia. This condition occurs when your red blood cells break down rapidly and your bone marrow can’t replace them quickly enough.
Your doctor may also order this test if you have already been diagnosed with hemolytic anemia. In this case, the test can help your doctor monitor your condition.
There are two types of hemolytic anemia.
Extrinsic hemolytic anemia
If you have extrinsic hemolytic anemia, your body produces normal red blood cells. However, they are destroyed too quickly because of an infection, an autoimmune disorder, or a particular type of cancer.
Intrinsic hemolytic anemia
If you have intrinsic hemolytic anemia, your red blood cells themselves are defective and naturally break down quickly. Sickle cell anemia, thalassemia, congenital spherocytic anemia, and G6PD deficiency are all conditions that can lead to hemolytic anemia.
Both types of hemolytic anemia cause the same symptoms. However, you may have additional symptoms if your anemia is caused by an underlying condition.
In the early stages of hemolytic anemia, you may feel:
You may also experience headaches.
As the condition progresses, your symptoms will become more serious. Your skin may become yellow or pale, and the whites of your eyes may become blue or yellow. Other symptoms may include:
- brittle nails
- heart issues (an increased heart rate or heart murmur)
- dark urine
- an enlarged spleen
- an enlarged liver
- tongue soreness
A serum hemoglobin test requires a small sample of blood to be drawn from your hand or your arm. This process usually only takes a few minutes:
- Your doctor or nurse will apply an antiseptic to the area where your blood will be drawn.
- An elastic band will be tied around your upper arm to increase the amount of blood flow to the veins, causing them to swell. This makes it easier to find a vein.
- Then, a needle will be inserted into your vein. After the vein is punctured, the blood will flow through the needle into a small tube that’s attached to it. You may feel a slight prick when the needle goes in, but the test itself isn’t painful.
- Once enough blood is collected, the needle will be removed and a sterile bandage will be applied over the puncture site.
Collected blood is then sent to a lab for testing.
Serum hemoglobin is measured in grams of hemoglobin per deciliter of blood (mg/dL). Lab results vary so your doctor will help determine if your results are normal or not. If your results come back normal, your doctor may want to do further testing.
High levels of hemoglobin in your serum are generally a sign of hemolytic anemia. Conditions that can cause red blood cells to break down abnormally include, but are not limited to:
- sickle cell anemia: a genetic disorder that causes your red blood cells to be rigid and unusually shaped
- G6PD deficiency: when your body does not make enough of the enzyme that produces red blood cells)
- hemoglobin C disease: a genetic disorder that leads to the production of abnormal hemoglobin
- thalassemia: a genetic disorder that affects your body’s ability to produce normal hemoglobin
- congenital spherocytic anemia: a disorder of your red blood cell membranes
If the results of your test are abnormal, your doctor will probably perform more tests to determine exactly what is causing hemolytic anemia. These additional tests may be simple blood or urine tests, or they may involve testing your bone marrow.
The only risks involved in this test are those always associated with a blood draw. For example, you will probably experience slight pain when the needle is inserted to draw your blood. You might bleed a little when the needle is removed or develop a small bruise in the area.
Rarely, a blood draw may have more serious consequences, such as excessive bleeding, fainting, or an infection at the puncture site.