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Information ⬇

Synonym/Acronym

red blood cell osmotic fragility, OF.

Rationale

To assess the fragility of erythrocytes related to red blood cell (RBC) lysis toward diagnosing diseases such as hemolytic anemia.

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

(Method: Spectrophotometry) Functional testing of RBCs by hemolysis (unincubated) begins in a hypertonic sodium chloride (NaCl) solution (e.g., 0.75%), is measured at a series of less hypertonic (incubated) solutions, and is complete (incubated) at 0.3% NaCl solution. Results are plotted and compared to a normal curve.

Osmotic fragility by hemolysisNormal: Within normal range curve (by comparing patient sample to known normal control)
RBC Band 3 Protein Reduction by flow cytometryNormal: No reduction in RBC Band 3 fluorescence detected; findings decrease the possibility of hereditary spherocytosis (HS)

Critical Findings and Potential Interventions ⬆ ⬇

N/A

Overview ⬆ ⬇

(Study type: Blood collected in a green-top [heparin] tube and two peripheral blood smears for spectrophotometry method; lavender-top [EDTA] or green-top [sodium or lithium heparin] and a Wright stained peripheral blood smear for flow cytometry; related body system: Circulatory/hematopoietic system.)

Osmotic fragility (OF) is an indication of the ability of RBCs to experience osmotic stress and take on water without lysing. Normal RBC membranes must be flexible to changes in plasma concentrations of electrolytes and other substances. In this functional test, RBCs are placed in graded dilutions of NaCl. Swelling of the cells occurs at lower concentrations of NaCl as they take on water in the hypotonic solution; that is, the concentration of electrolyte is higher inside the RBC, and in order to establish equilibrium with the surrounding fluid, the RBC must take on water by osmosis. Normal RBCs can absorb an increased volume; because of their biconcave shape, they have more surface area and can swell. Thicker cells, such as spherocytes, have an increased OF because they are already spherical, already have weak membranes, and cannot take on more volume without lysing; thinner cells have a decreased OF.

The RBC Band 3 study by flow cytometry is recommended to assist in the diagnosis of HS along with family history, clinical signs and symptoms, examination of peripheral smears for the presence of spherocytes, osmotic fragility, and genetic testing. Band 3 is the most plentiful transmembrane protein in human RBCs. A dye that binds to RBC Band 3 is added to the flow cytometer. The dye binds to RBCs with normal membranes. Decreased dye binding (less than normal) is reported in specimens of patients with HS.

Indications ⬆ ⬇

Evaluate hemolytic anemia.

Interfering Factors ⬆ ⬇

Other Considerations

  • Specimens should be submitted for analysis immediately after collection.

Potential Medical Diagnosis: Clinical Significance of Results ⬆ ⬇

Increased In

Conditions that produce RBCs with a small surface-to-volume ratio or RBCs that are rounder than normal will have increased osmotic fragility.

  • Acquired immune hemolytic anemias (abnormal RBCs in size and shape; spherocytes)
  • Hemolytic disease of the newborn (abnormal RBCs in size and shape; spherocytes)
  • Hereditary spherocytosis (abnormal RBCs in size and shape; spherocytes)
  • Malaria (related to effect of parasite on RBC membrane integrity)
  • Pyruvate kinase deficiency (abnormal RBCs in size and shape; spherocytes)

Decreased In

Conditions that produce RBCs with a large surface-to-volume ratio or RBCs that are flatter than normal will have decreased osmotic fragility.

  • Asplenia(abnormal cells are not removed from circulation due to absence of spleen; target cells)
  • Hemoglobinopathies (abnormal RBCs in size and shape; target cells, drepanocytes)
  • Iron-deficiency anemia (abnormal RBCs in size and shape; target cells)
  • Liver disease (abnormal RBCs in size and shape; target cells)
  • Thalassemias (abnormal RBCs in size and shape; target cells)

Nursing Implications ⬆

Before the Study: Planning and Implementation

Teaching the Patient What to Expect

  • Explain that a blood sample is needed for the test.
  • Discuss how this test can assist in assessing for anemia. Symptoms of anemia include chest pain, dizziness, fatigue, hands and feet that feel cold, headache, irregular pulse, pale skin, shortness of breath, and weakness. Additional symptoms of hemolytic anemia include jaundice (related to the accumulation of excessive amounts of bilirubin in the sclera and skin) and development of gallstones (related to abnormal elevations of bilirubin in the bile, which may lead to cholecystitis and formation of gallstones).

After the Study: Implementation & Evaluation Potential Nursing Actions

Treatment Considerations

  • Interventions/actions include the following: Monitor and trend bilirubin, Hgb/Hct, and RBC count. Explain that RBC transfusion(s) may be ordered to treat the anemia. Observe the patient for development of jaundice.
  • Note that splenectomy may be performed in the presence of significant anisocytosis (variations in RBC size) and/or poikilocytosis (variations in RBC shape) to reduce massive splenic destruction of the abnormal RBCs which would lead to anemia.

Clinical Judgement

  • Consider ways to provide culturally appropriate information related to potential blood transfusion.

Follow-Up Evaluation and Desired Outcomes

  • Acknowledges that additional testing may be necessary to monitor disease progression or evaluate the need for a change in therapy.