An inexpensive, rapid, convenient screening tube test for the detection of hemoglobin S and non-S sickling hemoglobins has been developed, which has a molecular basis. The reagents consist of potassium phosphate, sodium dithionite, and saponin. When sickling red cells are introduced into such a solution, the red cells lyse immediately, the hemoglobin deoxygenates, the beta globin chains of each hemoglobin tetramer are displaced laterally, complementarity of steric fit between interacting hemoglobin tetramers is achieved in accordance with the recently modified Murayama hypothesis for the molecular mechanism of sickling, a nematic liquid crystal system is formed, and in the presence of hemoglobin S or non-S sickling hemoglobins, the system becomes turbid. On addition of urea, those nematic liquid crystal systems dependent upon hydrophobic bonds are dispersed.

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Automated adaptations of dithionite and urea—dithionite tube tests are accurate, reliable, inexpensive methods for detecting hemoglobin S. More than 3,000 individuals have been screened (120 determinations per hour; reagent cost, 2 to 4 cents per test). The dithionite reagent consists of potassium phosphate, sodium dithionite, and saponin. When S hemoglobin contacts this reagent, the red cells lyse, and the hemoglobin deoxygenates and sickles, forming a hydrophobic-bond-dependent nematic liquid crystal system that is manifested as turbidity. The resulting AutoAnalyzer curve is strikingly and diagnostically different from that produced by hemoglobin A in the same reagent. Specificity of the automated dithionite test may be enhanced by use of the automated urea—dithionite test, which consists of a specimen set of two aliquots: one traverses a dithionite line, the other a urea—dithionite line. A comparison of transmittance in the two lines yields typical diagnostic curves because the urea disperses the sickling, with a consequently increased transmittance over that of the dithionite aliquot. Methods are discussed for recognizing non-S sickling hemoglobins and a few other rare hemoglobinopathies.