OFT - OFT hematology PDF

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OFT hematology...

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Osmotic Fragility test   

Measure of the ability of the red cells to take up fluid without lysing. This is to help diagnose different types of anemias, in which the physical properties of the red blood cell are altered. Primary factor affecting OFT o Shape of Red cell, o in which turn depends on the volume, o surface area, o And functional state of the red blood cell membrane.

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Factor affecting OFT Test o Chemical purity of sodium chloride o Accuracy of sodium chloride solution o Tonicity of solution o PH must be 7.4 (a change of PH by 0.1 is equal to the change of tonicity by 0.01%) o A temperature rise will increase fragility (a 5®C change is equal to a change of tonicity of about 0.01%) o Erythrocyte (Shape ,Volume ,Surface area, Membrane Function)

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The larger the amount of red cell membrane (surface area) in relation to the size of the cell, o The more fluid the cell is capable of absorbing before rupturing (it is more resistant to hemolysis and has decreased fragility).

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The target cell has the largest surface area (amount of membrane) for its size and therefore shows decreased fragility.

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As the red cell takes in fluid it becomes more round (spherocytic). o It therefore follows that the spherocyte has the smallest surface area for its volume, o ruptures the most quickly, o And has increased fragility.

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Increased osmotic fragility (decreased resistance) is found in o Hemolytic anemias o and hereditary spherocytosis, o And whenever spherocytes are found.

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Decreased osmotic fragility (increased resistance) occurs following o splenectomy and o in liver disease, o sickle cell anemia, o iron-deficiency anemia, o thalassemia and

o o 

polycythemia Vera, And conditions in w/ target cells are present.

Reticulocytes show decreased osmotic fragility; the older red cells are also more fragile.

METHODS OF OSMOTIC FRAGILITY TEST       

Sanford method Modified method Griffith and Sanford Dacie Incubation method Unopette method Fragiligraph method

INTERPRETATION Increase OFT- Cells like Spherocytes have limited capacity to expand in hypotonic solution & therefore lyse @ higher concentration of NaCl solution than normal biconcave Red cell. Decrease OFT- cells like Target cells in thalassemia are flatter cells. IDA have a greater capacity to expand in hypotonic solution and lyse @ lower concentration of sodium chloride solution than normal RBC.

SANFORD METHOD Principle: It test the stability of Red blood cells under different concentration of hypotonic NaCl solution. Materials needed.        

12 TT (3-5ml) Time TT Rack Viewer Dropper 0.5% NaCl Distilled water Fresh/Defibrinated/ Heparinized blood

Procedure: Ara sa Lab manual. Interpretation:   

No hemolysis – With compact sediment & clear Solution Initial Hemolysis- With not so compact Sediment & Faint Pink Solution Complete Hemolysis- Without Sediment and Dark Red Solution. (Normal Values for IH: 0.42%—0.44%) (NV for CH: 0.32%- 0.34%)...