**Question:** Test for detection of old blood stain is

A. Hemastix
B. Latex test
C. Coomassie Brilliant Blue (CBB)
D. Periodic Acid Schiff (PAS)

**Core Concept:** Tests for the identification of bloodstains involve various methods to detect the presence of hemoglobin, which is the primary component of blood. These tests are used in forensic science to establish the age of a bloodstain, differentiate between fresh and old bloodstains, and provide crucial information for case investigations.

**Why the Correct Answer is Right:** The correct answer, D. Periodic Acid Schiff (PAS) test, is used to detect the presence of hemoglobin in a bloodstain, specifically its glycosaminoglycans. Hemoglobin is converted into a highly reactive intermediate, which reacts with PAS reagent, producing a pink color that is easily distinguishable from other substances. This test is specifically designed to detect old bloodstains, making it suitable for determining the age of a bloodstain.

**Why Each Wrong Option is Incorrect:**

A. Hemastix: Although Hemastix is a urine dipstick test that detects the presence of hemoglobin in urine, it cannot accurately identify the age of a bloodstain. Hemastix is primarily used for urine analysis, not bloodstain detection.

B. Latex test: This test is primarily used for detecting the presence of proteins, not specifically hemoglobin or old bloodstains. Thus, it is not suitable for determining the age of a bloodstain.

C. Coomassie Brilliant Blue (CBB): CBB is a staining technique used for protein detection in electrophoresis, not for bloodstain identification or age determination.

**Clinical Pearl:** In forensic investigations, it is essential to choose the appropriate test for detecting bloodstains, especially when determining the age of the bloodstain. The choice of test depends on the specific requirements of the case, such as the age of the bloodstain, substrate (e.g., fabric, wood, concrete) and the presence of other substances or stains. In the context of determining the age of bloodstains, Periodic Acid Schiff (PAS) test is the most suitable choice, whereas Hemastix and Latex tests are not suitable for this purpose. Coomassie Brilliant Blue is a staining technique for proteins and is not relevant to bloodstain analysis.