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

Which preservative in a 24-hour urine collection interferes the least with dipstick analysis?

1. HCl (Hydrochloric acid)

2. Boric acid

3. Acetic acid

4. Formalin

The correct answer is: Boric acid

Boric acid is the preservative that interferes the least with dipstick analysis in a 24-hour urine collection. It serves primarily as a gentle antimicrobial agent, preventing bacterial growth without significantly altering the chemical composition of the urine. This characteristic is crucial for accurate dipstick testing, which relies on specific chemical reactions to provide reliable results. In contrast, other preservatives can result in more substantial interactions with the dipstick reagents. For example, hydrochloric acid can lower the pH of the urine drastically, which may affect readings for things such as protein or glucose. Acetic acid, while it may have some uses in preserving urine, can similarly impact the pH and may also influence other parameters being tested. Formalin, used primarily in histopathology for tissue preservation, can greatly interfere with the dipstick analysis by affecting color reactions and skewing results, as it alters the protein content and can produce false positives or negatives. Thus, the characteristics of boric acid make it the most suitable choice among preservatives when conducting dipstick analysis, ensuring that the urine chemistry remains as unaltered as possible for reliable assessments.