Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Which of the following tests is most commonly performed on a skin puncture sample?

1. HCT

2. pH

3. PKU

4. PTT

The correct answer is: PKU

The most commonly performed test on a skin puncture sample is the phenylketonuria (PKU) screening test. This test is particularly important for newborns and young infants, as it identifies defects in the metabolism of phenylalanine, an amino acid that, if not properly metabolized, can lead to serious neurological issues. Since skin puncture samples, often collected via heel prick in infants, require a limited volume of blood, PKU testing is well-suited for this method. It is a quick, cost-effective, and essential screening tool to ensure that infants are healthy and developing normally. In contrast, tests such as hematocrit (HCT), which measures the proportion of blood volume that is occupied by red blood cells, can be performed using venous blood samples for greater accuracy and reliability. Similarly, pH testing typically requires a more controlled environment and accurate sample handling, making it less suitable for skin punctures. Prothrombin time (PTT), a test that assesses blood clotting ability, is generally performed on larger venous blood samples to accurately determine coagulation factors, thereby ruling it out as a common application for skin puncture specimens.