(3) Unstoppered tubes containing dithionite reagent decompose when left
out at room temperature.
(4) False negative results could occur if the blood sample for testing is
drawn within 4 months of transfusion.
(1) Hemoglobin S is an inherited type of hemoglobin found primarily in
blacks and people from Mediterranean areas.
(2) The degree of erythrocyte sickling is dependent on the concentration of
hemoglobin. SS, SC, and SD cells sickle more rapidly than AS cells. Newborns with
sickle cell anemia have erythrocytes more resistant to sickling due to the presence of
(3) The dithionite test also detects other sickling types of hemoglobin. Urea
causes hemoglobin S (and structural variants of hemoglobin S) to dissolve. Other
hemoglobins remain turbid in the presence of urea.
(4) This test is a rapid screening test for hemoglobin S. All positive
dithionite tests should be electrophoresed for confirmation.
f. Interpretation. Hemoglobin S causes turbidity in the tube. Hemoglobin A is
soluble in the phosphate buffer.
6-12. DEMONST4RATION OF THE SICKLE CELL PHENOMENON
a. Principle. Erythrocytes of persons with sickle cell anemia or trait will assume
a sickle shape when the oxygen tension is lowered. This may be demonstrated by
mixing a drop of blood with a reducing agent such as sodium metabisulfite.
b. Reagent. Sodium metabisulfite, 2 percent. Add 2 g of sodium metabisulfite
to a 100-ml volumetric flask. Dilute to the mark with distilled water. This solution, if
stored at 3 or 4C remains effective for about 1 week.
(1) Place 1 drop of capillary (or venous without anticoagulants) blood on a
clean glass slide.
Add 1 or 2 drops of 2 percent aqueous sodium metabisulfite and mix.
(3) Place a cover glass on the preparation and express the excess blood by
gently pressing the cover glass. The gentle pressure will produce a film thin enough to
permit examination of individual red cells. It is not necessary to seal the preparation.