American Society for Clinical Pathology (ASCP) Histotechnician Certification Practice Exam

Which marker is best for ensuring a complete 24-hour urine collection?

1. Creatinine level

2. Urea nitrogen level

3. 4-aminobenzoic level

4. Glucose level

The correct answer is: 4-aminobenzoic level

The best marker for ensuring a complete 24-hour urine collection is 4-aminobenzoic acid (PABA). This compound is often used as a test substance because it is easily measurable and is excreted in urine in a consistent manner. When conducting a 24-hour urine collection, administering PABA allows for verification of whether the patient has collected urine over the entire 24-hour period. If any urine is discarded or if the collection is incomplete, the levels of PABA will be lower than expected, alerting the technician to the collection's incompleteness. In contrast, while creatinine, urea nitrogen, and glucose levels can also be assessed in a 24-hour urine collection, they do not specifically serve as markers to confirm that the entire collection was carried out properly. Creatinine is commonly measured to estimate kidney function, but variations in its levels can occur due to dietary intake, hydration status, and muscle mass, and therefore it does not offer reliable confirmation of collection completeness. Urea nitrogen is utilized for similar purposes in assessing kidney function or protein metabolism but has the same limitations. Glucose levels vary markedly based on dietary intake and other factors, and while they can indicate certain metabolic conditions, they do not inherently confirm the