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SICKLE CELL ANEMIA

2 DEFECTS

• Quantitative defects: Ex. Thalassemias – haemoglobins Hb A, Hb A2, Hb F abnormally distributed.
• Qualitative defects: Ex. Sickle cell anaemia – abnormal haemoglobin (Hb S) is formed.
• Red cells with haemoglobin S-S (Hb S-S) are abnormal in shape, narrow, crescent shaped with defective membranes.
• Hb S is insoluble when oxygen tension is lowered and this makes red cells susceptible to sickling.
• Sickled cells tend to clump together and Cannot freely flow through the circulation.
• It blocks blood supply in small blood vessels by these red cell clumps.
• It cause pain and easily haemolysed due to abnormal shapes.

• Causes chronic haemolytic anaemia.
• LABORATORY DIAGNOSIS:
• **Based on three observations:

1. Sickling of red cells under deoxygenated conditions
2. Precipitation of haemoglobin S in a special medium
3. Haemoglobin electrophoresis (confirmatory test).**

SCREENING TEST

• It does not differentiate sickle cell trait from sickle cell disease.
• SICKLE CELL PREPARATION:
• PRINCIPLE:
• Whole blood mixed with sodium metasulphite, a strong reducing agent that deoxygenates haemoglobin.
• If cells contain Hb S, they become sickle shaped or half moon shaped.
• EQUIPMENT AND SUPPLIES:
• Dropper, Pasteur pipette, petridish, slide, cover slip, filter paper, syringe, microscope, sodium metabisulphite.

PROCEDURE

• A small drop of blood (20 mu lt) on slide.
• Add sodium metabisulphite solution by Pasteur pipette.
• Keep slide on petri dish with wet filter paper and cover it.
• Mix it
• Cover the cover slip.
• With syringe cover the rim of cover slip with petroleum jelly to seal.
• Wait for 15 min.
• Observe under microscope.
• Sickling is visible immediately in case of sickle cell disease (Hb S-S) and in sickle cell trait (Hb S-A) within 60 min.
• If negative reexamine after 2 hr and after 24 hr.
• The red cells remain round (unchanged) when it is negative.

2. SOLUBILITY TEST FOR SICKLE CELL - Observed visually and no microscope. - More sensitive. - SPECIMEN: - EDTA-anticoagulated venous blood, heparinized capillary blood or citrated blood can be used. - Fresh specimen is not necessary. - PRINCIPLE: - Haemoglobin S in the reduced state is less soluble than the normal Hb A. - Dithionite in phosphate buffer reduces Hb S forms a turbid suspension of protein crystals. - These crystals prevent reading of lines on a paper card. - Saponin is used to lyse the red cells.

• REAGENT:

• Dithionite solution:
• Dibasic potassium phosphate:
• Anhydrous K2HPO4 – 21.6 g
• Monobasic potassium phosphate:
• Anhydrous crystals KH2PO4 – 16.9 g
• Sodium dithionite Na2S2O4 – 0.5 g
• Saponin – 0.1 g