 Fetal hemoglobin is resistant to alkali (basic) denaturation, whereas adult hemoglobin is susceptible to such denaturation.Therefore, exposing the blood specimen to sodium hydroxide (NaOH) will denature the adult but not the fetal hemoglobin.The fetal hemoglobin will appear as a pinkish color under the microscope while the adult hemoglobin will appear as a yellow-brownish color.