What is an osmotic fragility test?

An osmotic fragility test can be used to help diagnose two hereditary conditions: thalassemia and hereditary spherocytosis:

  • Thalassemia causes your body to make an abnormal form of hemoglobin. Hemoglobin is the protein that allows red blood cells to carry oxygen. If you have thalassemia, your red blood cells are more likely to be destroyed. This can lead to anemia.
  • Hereditary spherocytosis causes problems with the outer layer of your red blood cells, distorting their shape. This leads to more fragile red blood cells and early destruction, which can also cause anemia.

For an osmotic fragility test, you’ll need to give a blood sample. Your red blood cells will be tested to see how easily they break apart in a salt solution. If your red blood cells are more fragile than normal, the test is considered positive.

Doctors may order osmotic fragility tests for infants with a family history of thalassemia or hereditary spherocytosis. This can be a fast and cost-effective way to help diagnose the disease.

However, sometimes the condition needs to be confirmed with other blood tests or genetic testing. This is because certain other conditions may also give similar results.

The osmotic fragility test may also be used to help confirm if thalassemia or spherocytosis is the cause of anemia. Symptoms of anemia can include:

  • fatigue
  • shortness of breath
  • dizziness
  • palpitations
  • decreased ability to exercise

There are no special preparations required for the test. It’s a simple blood test, also known as a venipuncture. It can be performed in either a lab or a doctor’s office.

If you’re wearing a long-sleeved shirt, the technician will ask you to roll up one of your sleeves or to remove your arm from the sleeve.

The technician will tie an elastic strap tightly around your upper arm to help blood pool in the veins. You may find this part of the process uncomfortable.

The technician will find a vein and clean the area with an antiseptic. They’ll insert a hollow needle into the vein. For most people, this sensation feels like a sharp pinch.

After collecting enough blood, the technician will remove the needle. You’ll need to keep pressure on the puncture for a few seconds. Then the technician will cover the spot with a bandage.

Having blood drawn carries few risks. The greatest risk, which occurs extremely rarely, is infection.

Tell your doctor if you start running a temperature above 100°F. You should also seek help if the skin around the puncture becomes red, swollen, or painful to touch.

For a few days after the test, the skin around the puncture may be bruised or tender. This is normal. Applying a cool compress to the area can reduce bruising and ease discomfort. Unless your doctor tells you otherwise, you’re free to resume all normal activities after the test.

The lab will prepare your blood. To test osmotic fragility, your red blood cells will be added to solutions with different salt concentrations. Normal blood cells are better able to remain intact at low salt solutions than the more fragile blood cells of spherocytosis or thalassemia.

If your cells are diagnosed as fragile, you most likely have hereditary spherocytosis or thalassemia. Both of these genetic conditions can cause hemolytic anemia. This is a form of anemia that occurs because your red blood cells are destroyed too quickly.

If your osmotic fragility test is positive, the next step is to confirm the results and test whether you are actively anemic.

Not everyone with these diseases will have the same level of symptoms. Some people will have only mild forms with occasional symptoms. Others will have severe forms that require immediate treatment and may affect life span.

Once your doctor determines the level of your condition, you’ll discuss your treatment needs. If your illness is mild and you have few symptoms, watchful waiting may be all that’s necessary. Treatment for severe disease will depend on your specific diagnosis.