Cord red blood cells from an infant suspected of having hemolytic disease of the newborn is most likely to be tested by which of the following?
**Core Concept**
Hemolytic disease of the newborn (HDN) is a condition where the immune system of the mother produces antibodies against the red blood cells of the fetus, leading to their destruction. Direct antiglobulin test (DAT) is a laboratory test used to detect the presence of antibodies or complement on the surface of red blood cells.
**Why the Correct Answer is Right**
The DAT is used to diagnose HDN by detecting the presence of maternal antibodies or complement on the surface of the infant's red blood cells. This is typically seen in conditions where the mother has Rh or ABO incompatibility with the fetus. The test involves adding antiglobulin antibodies to the blood sample to detect any antibodies or complement bound to the red blood cells. This is a critical test in diagnosing HDN, as it helps in understanding the severity of the disease and guiding further management.
**Why Each Wrong Option is Incorrect**
**Option A:** The direct Coombs test is the same as the direct antiglobulin test, so it is also correct. (This option is correct, but not necessary to explain as it's not a distractor.)
**Option B:** The indirect Coombs test is used to detect the presence of antibodies in the serum that can bind to red blood cells, but it is not used to test cord blood for HDN.
**Option C:** The complete blood count (CBC) is a basic test that provides information on the different components of blood, but it does not specifically diagnose HDN.
**Option D:** The Kleihauer-Betke test is used to detect the presence of fetal hemoglobin in maternal blood, which is not relevant to diagnosing HDN.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the DAT is a critical test in diagnosing HDN, and it should be performed in infants with suspected HDN to guide further management.
**Correct Answer:** C. Direct antiglobulin test (DAT).