Test used to differentiate maternal and fetal blood is-
**Core Concept**
The differentiation between maternal and fetal blood is crucial in various clinical scenarios, including postpartum hemorrhage and prenatal diagnosis. This requires a test that can distinguish between the two types of blood based on their unique characteristics.
**Why the Correct Answer is Right**
The correct answer is the Apt test, also known as the Apt-Downey test. This test is based on the principle that fetal hemoglobin is more resistant to alkaline denaturation than adult hemoglobin. When a blood sample is mixed with a solution of sodium hydroxide (NaOH), the adult hemoglobin in maternal blood will denature and precipitate out of solution, whereas the fetal hemoglobin in fetal blood will remain dissolved. This results in a clear or pale yellow color in the presence of fetal blood, distinguishing it from maternal blood, which will appear cloudy or milky.
**Why Each Wrong Option is Incorrect**
**Option A:** The Kleihauer-Betke test is used to detect fetal-maternal hemorrhage, but it is not used to differentiate between maternal and fetal blood.
**Option B:** The Apt test is not the same as the Apt test used in pediatric gastroenterology to diagnose congenital esophageal atresia or tracheoesophageal fistula.
**Option C:** The direct Coombs test is used to detect the presence of antibodies against red blood cells, but it is not used to differentiate between maternal and fetal blood.
**Clinical Pearl / High-Yield Fact**
The Apt test is a simple, rapid, and inexpensive method for differentiating between maternal and fetal blood, making it a valuable tool in various clinical settings.
**Correct Answer:** C.