Lab Dept:


Test Name:

Osmotic Fragility

General Information

Lab Order Codes:



RBC Fragility; Erythrocyte Fragility; Incubated Osmotic Fragility

CPT Codes:

85557 – Osmotic fragility, RBC; incubated

Test Includes:

Percent hemolysis of red blood cells for unincubated specimens placed in 0.50 g/dL concentration of NaCl and incubated specimens (37°C for 24 hours) when tested in NaCl concentrations of 0.60, 0.65 and 0.75 g/dL.


Test Indications:

Useful for suspected hereditary spherocytic hemolytic anemia.

Lab Testing Sections:

Hematology - Sendouts

Referred to:

Mayo Medical Laboratories (MML Test: 9064/FRAG)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

2 – 5 days (performed Monday – Saturday, reported Monday - Friday)

Special Instructions:

Indicate patient’s date of birth on request form. Specimen must arrive at reference lab within 96 hours of draw.


Specimen Type:

Whole blood


Lavender top (EDTA) tube

Draw Volume:

5 mL (Minimum: 2 mL)  blood

Processed Volume:

Same as Draw Volume


A trauma-free blood collection required


Special Processing:

Send 5 mL EDTA blood refrigerated. Specimen should remain in original collection container. Do not transfer blood to another tube. Do not centrifuge.

Also, send a 5 mL fresh EDTA whole blood specimen from a normal, untreated person at the same time, refrigerate and Label as normal control, indicate sex of the person from whom the control was drawn on the specimen label.

Do Not freeze.

Patient Preparation:


Sample Rejection:

Clotted; frozen; mislabeled or unlabeled specimen; gross hemolysis


Reference Range:

0.50 g/dL NaCl (unincubated)

Males: 0.0 – 47.8% hemolysis

Females: 0.0 – 31.1% hemolysis

0.60 g/dL NaCl (incubated)

Males: 18.7 – 67.4% hemolysis

Females: 10.9 – 65.5% hemolysis

0.65 g/dL NaCl (incubated)

Males: 4.4 – 36.6% hemolysis

Females: 0.2 – 39.3% hemolysis

0.75 g/dL NaCl (incubated)

Males: 0.8 – 9.1% hemolysis

Females: 0.0 – 10.9% hemolysis

Interpretation: Increased lysis in 3 or more concentrations of sodium chloride indicates red cell fragility.

Critical Values:



Infrequently, other hemolytic disorders may be associated with positive results, as in patients with congenital nonspherocytic hemolytic anemia due to G-6-PD or pyruvate kinase deficiency.

Patients with an immunohemolytic anemia, or who have recently received a blood transfusion may also have increased RBC lysis.


Osmotic Lysis


Recent transfusion


Mayo Medical Laboratory Web Page August 2013


11/6/2006: Updated reference ranges.