Definition

The osmotic fragility of erythrocyte test is a diagnostic procedure used to assess how susceptible red blood cells (erythrocytes) are to rupturing. Normal red blood cells are biconcave in shape, providing them with a relatively impermeable surface that helps maintain osmotic balance with their surrounding environment. Under normal conditions, when the environment becomes hypotonic, water enters the red blood cells to balance the osmotic pressure. However, if the environment becomes excessively hypotonic, the cells will absorb too much water, leading to rupture. Red blood cells shaped like spheres (spherocytes) have a reduced capacity to expand, and they will rupture in conditions that typically would not affect normal red blood cells. This indicates a reduction in osmotic fragility.

The test measures the extent of hemolysis (rupture of red blood cells) in a hypotonic salt solution. If hemolysis occurs at a sodium chloride concentration of more than 0.5%, the osmotic fragility is considered decreased. In the case of hereditary spherocytosis, the reduced osmotic fragility may only be visible in a small percentage of cells that are more prone to rupture. Incubation is sometimes used to enhance the visibility of the abnormality, making the increased susceptibility of cells in hereditary spherocytosis more apparent. If hemolysis does not occur completely in a 0.3% salt solution, osmotic fragility is considered to be increased.

Indication

Your doctor may recommend the osmotic fragility of erythrocyte test if you exhibit symptoms of anemia (a condition characterized by a shortage of red blood cells), such as:

• Headache

• Dizziness or light-headedness

• Fatigue

• Chest pain

• Irregular heartbeat

• Cold hands and feet

• Weakness

• Irregular breathing

• Yellowish or pale skin

Contraindication

Contraindications for blood sampling are generally related to conditions affecting the area from which the blood is being drawn. For example, infections in the sampling area increase the risk of bacteria entering the bloodstream. Other contraindications include the presence of blood vessel grafts, bruising, or hardening of the arteries.

Preparation Before the Test

No special preparation is required before the osmotic fragility of erythrocyte test.

Test Procedure

The test requires a blood sample. You may experience a mild stinging or pain when the needle is inserted, but this discomfort is typically short-lived. After the blood is drawn, you may feel slight pain or notice bruising at the injection site.

In the laboratory, the red blood cells are exposed to a solution that causes them to swell, allowing the technician to assess the fragility of the cells.

Normal and Abnormal Value

The degree of hemolysis in different sodium chloride (NaCl) concentrations is as follows:

• 5 g/dL NaCl (without incubation): 3-53% hemolysis

• 6 g/dL NaCl (with incubation): 14-74% hemolysis

• 65 g/dL NaCl (with incubation): 4-40% hemolysis

• 75 g/dL NaCl (with incubation): 1-11% hemolysis

A normal test result is considered negative, meaning no abnormal hemolysis is observed.

The normal range can vary slightly between different laboratories, as some labs may use different measurement techniques. Be sure to consult your doctor for clarification on your test results.

Results and Recommendations (Follow-up Tests)

Decreased fragility of erythrocyte can indicate two major conditions: thalassemia and hereditary spherocytosis.

• Thalassemia is an inherited blood disorder caused by mutations in the DNA, leading to abnormalities in hemoglobin, the protein responsible for carrying oxygen in red blood cells. This results in anemia due to insufficient or dysfunctional hemoglobin.

• Hereditary Spherocytosis is another inherited condition that causes the red blood cell membrane to become fragile. This condition leads to anemia as the red blood cells are more prone to breaking down.

Both thalassemia and hereditary spherocytosis can cause hemolytic anemia, where the destruction of red blood cells occurs at a faster rate than their production, leading to a low red blood cell count.

Although decreased osmotic fragility is a hallmark of hereditary spherocytosis, it can also be observed in other types of hemolytic anemia, especially those involving spherocytic red blood cells. This includes autoimmune hemolytic anemia and conditions like hypernatremia (elevated sodium levels), where blood sodium concentrations exceed 155 meq/L. Additionally, individuals who have recently undergone a blood transfusion may experience increased red blood cell breakdown (hemolysis).

On the other hand, increased osmotic fragility is associated with chronic liver disease, iron deficiency anemia, hyponatremia (sodium levels below 130 meq/L), polycythemia vera, and sickle cell anemia following spleen removal.

To diagnose hereditary spherocytosis more accurately, additional tests such as flow cytometry using eosin-5'-maleimide (EMA) and flow-cytometric osmotic fragility tests (FOFT) can be performed.

Research has shown that both flow cytometry tests yield more precise results than traditional osmotic resistance tests. In fact, combining the EMA and FOFT tests can provide a 100% accurate diagnosis. As a result, these tests are expected to become the standard method for diagnosing hereditary spherocytosis in the future.

Consult the Right Doctor

If you have abnormal erythrocyte osmotic resistance test results, it’s advisable to consult an internal medicine specialist. The doctor will help determine the underlying cause and provide appropriate treatment.

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