<prompt> The reagent used in the Apt test?Sodium hydroxideSodium chloridePotassium ChlorideSodium bicarbonate  <response>: Alkali denaturation test Apt-Downey test apt test-Used to detect differentiate Fetal or neonatal blood from maternal blood Qualitative.PrincipleMethodvFetal hemoglobin alpha 2 gamma 2 subunits is resistant to alkali basic denaturation, whereas adult hemoglobin alpha2 beta 2 subunits is susceptible to such denaturation.vExposing the blood specimen to sodium hydroxide NaOH will denature the adult but NOT the fetal hemoglobin.vThe fetal hemoglobin will appear as a pinkish color under the microscope while the adult hemoglobin will appear as a yellow-brownish colorvThe blood is mixed with sterile water to cause hemolysis of the RBCs, yielding free hemoglobin,vThe 5 ml pink hemoglobin-containing supernatant is then mixed with 1 mL of 1 NaOH.vFetal hemoglobin will stay pink and adult hemoglobin will turn yellow-brown.vAdult hemoglobin changes color because it is less stable and will conve to hematin. 