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Abbreviation for:
open field
operating framework 
organ failure
osmotic fragility
ossifying fibroma
oxidation fermentation

Osmotic Fragility

Synonym/acronym: Red blood cell osmotic fragility, OF.

Common use

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


Whole blood (1 mL) collected in a green-top (heparin) tube and two peripheral blood smears.

Normal findings

(Method: Spectrophotometry) Hemolysis (unincubated) begins at 0.5% sodium chloride (NaCl) solution and is complete at 0.3% NaCl solution. Results are compared to a normal curve.


Osmotic fragility (OF) is an indication of the ability of red blood cells (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 test, RBCs are placed in graded dilutions of sodium chloride (NaCl). Swelling of the cells occurs at lower concentrations of NaCl as they take on water in the hypotonic solution, i.e. 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 RBC can absorb an increased volume because of their bicocave 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.

This procedure is contraindicated for



  • Evaluate hemolytic anemia

Potential diagnosis

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)

Critical findings


Interfering factors

  • Drugs that may increase osmotic fragility include dapsone.
  • Parasitic infestations, such as malaria, may independently cause cell hemolysis.
  • Specimens should be submitted for analysis immediately after collection.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:  Inform the patient this test can assist in assessing for anemia.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include CBC, CBC RBC indices, CBC RBC morphology, culture blood, G6PD, Ham’s test, hemoglobin electrophoresis, iron, and PK.
  • Refer to the Hematopoietic System table at the end of the book for related tests by body system.
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