This test is used as a screening tool for?

Ref: Harsh Mohan Textbook of Pathology, 7th ed. pg. 292 and Wintrobe's Hematology, 13th ed. pg. 610* The image shows performance of Naked eye single tube, osmotic fragility test. Notice that in control sample on right side, the fine print of newspaper can be acknowledged.* However, in the left sided sample, osmotic fragility is reduced leading to turbidity, leading to opacification of sample and the fine print of the newspaper cannot be read.* This test is a screening test for thalassemia following which high performance liquid chromatography is done.