Overview
Osmotic fragility testing exposes RBCs to decreasing NaCl concentrations and quantifies hemolysis; spherocytes lyse at higher tonicities than normal discocytes.
Clinical Importance
As a supportive test when hereditary spherocytosis is suspected
In selected laboratories that still perform OFT alongside or instead of EMA binding
Specimen Requirements
- Anticoagulated whole blood (EDTA or heparin per local protocol)
- Test promptly; freshness affects results
- Avoid hemolyzed draws
Analytical Method
RBCs suspended in hypotonic saline take up water and lyse. The percentage hemolysis at each saline concentration is plotted. Incubated OFT (24 h at 37 °C) increases sensitivity for mild spherocytosis.
Instruments Used
Automated analyzers
- Spectrophotometers for supernatant hemoglobin measurement after controlled lysis
Manual methods
- Manual osmotic fragility tube series with spectrophotometric readout
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Results are reported as hemolysis curves versus a normal control run in parallel; absolute cutoffs are method-specific.
Interpretation
Common Causes of Increased Results
- Increased fragility (lysis at higher saline concentrations) supports a spherocytosis pattern when clinical and smear findings align
Common Causes of Decreased Results
- Decreased fragility may be seen with target cells / certain hemoglobinopathies; nonspecific
Clinical Significance
- Supportive laboratory evaluation when hereditary spherocytosis is in the differential
Factors Affecting Results
Pre-analytical
- Delayed testing, recent transfusion, and reticulocytosis alter curves
- Iron deficiency can reduce fragility
Analytical
- Inaccurate saline concentrations or temperature control
- Failure to run a normal control
Post-analytical
- Interpreting OFT without smear morphology
Advantages and Limitations
Advantages
- Classic physiologic demonstration of spherocyte fragility
Limitations
- Labor-intensive; imperfect sensitivity for mild disease
- EMA binding flow cytometry is preferred in many modern algorithms
Clinical Pearls
Always compare the patient curve to a same-day normal control; an OFT without a control is not interpretable.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
WHO Publications
- World Health Organization. Guide to G6PD testing and counselling for safe use of 8-aminoquinoline drugs. WHO; 2022.
Frequently Asked Questions
Common questions about using this Osmotic Fragility Test laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Osmotic Fragility Test laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Osmotic Fragility Test. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Osmotic Fragility Test specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Osmotic Fragility Test. Confirm collection details against your laboratory protocol.
Where are Osmotic Fragility Test reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Osmotic Fragility Test results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Osmotic Fragility Test?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Osmotic Fragility Test?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Osmotic Fragility Test?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for Osmotic Fragility Test?
See the Clinical Pearls section for concise laboratory practice notes associated with Osmotic Fragility Test. Apply pearls alongside institutional protocols.
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