[1][2] The test was developed by Leonard Apt (1922–2013),[3] an American pediatric ophthalmologist.
The test was originally used to identify the source of bloody stools in newborn infants.
It has been modified to distinguish fetal from maternal hemoglobin in blood samples from any source.
Therefore, exposing the blood specimen to sodium hydroxide (NaOH) will denature the adult but not the fetal hemoglobin.
The blood is mixed with a small amount of sterile water to cause hemolysis of the RBCs, yielding free hemoglobin.