The present invention provides a method for determining sickle-cell zygosity in a subject. The method involves forming a first solution which includes a sample from the subject, a phosphate buffer, a detergent, and a reducing agent and subjecting the first solution to centrifugation to form a second solution and a supernatant; and taking a color reading of the supernatant and of the second solution; optionally filtering the second solution to form a filtrate and a precipitate, and optionally measuring the amount of the precipitation and the absorbance of the filtrate or taking a color reading of the filtrate.