Reagent used in Apt test
**Core Concept**
The Apt test is a diagnostic tool used to differentiate between fetal and mature hemoglobin in a newborn's stool or vomit. It relies on the isomaltase enzyme present in mature red blood cells, which is sensitive to alkali. The test is performed by adding a reagent to the sample, causing it to change color based on the presence of fetal or mature hemoglobin.
**Why the Correct Answer is Right**
The correct reagent used in the Apt test is sodium hydroxide (NaOH). When NaOH is added to the sample, it breaks down the isomaltase enzyme in mature red blood cells, causing a color change. This reaction is specific to mature hemoglobin, allowing for the differentiation from fetal hemoglobin, which does not contain the isomaltase enzyme. The test is based on the principle that fetal hemoglobin is more resistant to alkali denaturation than mature hemoglobin.
**Why Each Wrong Option is Incorrect**
* **Option A:** Ammonium hydroxide is not the correct reagent used in the Apt test. While it is a strong base, it is not specific to the isomaltase enzyme and would not provide accurate results.
* **Option B:** Hydrochloric acid (HCl) is not used in the Apt test. HCl is a strong acid that would not break down the isomaltase enzyme and would likely interfere with the test results.
* **Option C:** Glucose is not a reagent used in the Apt test. Glucose is a simple sugar that is not involved in the reaction that differentiates between fetal and mature hemoglobin.
**Clinical Pearl / High-Yield Fact**
The Apt test is a simple and inexpensive method for differentiating between fetal and mature hemoglobin, but it requires careful handling and interpretation of the results. A positive test result indicates the presence of mature hemoglobin, which is often associated with gastrointestinal bleeding in newborns.
**Correct Answer:** D.