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- Address for Correspondence: Tim R. Randolph
, Saint Louis University, tim.randolph{at}health.slu.edu
ABSTRACT
The objective of this study was to develop a simple, inexpensive, and rapid confirmatory test using a sodium metabisulfite microscopic method to distinguish AS from SS genotype in patients with positive test results for hemoglobin S. Equal volumes of de-identified EDTA blood and 2% sodium metabisulfite were mixed, placed on a microscope slide with coverslip, and observed for sickling at 30-minute intervals over 3 hours. Sickle cells were enumerated per 200 red blood cells (RBCs) under 100x oil immersion and placed into 4 Likert categories (1+ to 4+) based on degree of sickling. In AS samples, 2+ and 3+ sickle cells rose most rapidly, and 4+ sickle cells showed the steepest rise in the SS samples. Based on these data, the number of 4+ sickle cells were counted every 30-minutes over 3 hours in 5 AS and 28 SS samples at 37°C. The mean numbers of 4+ sickle cells in AS samples were 4.75 per 200 RBCs at 2 hours and 17.75 per 200 RBCs at 3 hours. SS samples yielded 78.29 per 200 RBCs at 2 hours and 115.43 per 200 RBCs at 3 hours. Two-hour incubation showed a statistical difference (P = 0.00024) among groups in the shortest time and may be used to distinguish SS from AS genotypes. More testing is needed to determine cut points to distinguish genotype.
- Received August 22, 2019.
- Accepted October 9, 2019.
American Society for Clinical Laboratory Science
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