Which of the following will not contribute to the integrity of a urine specimen when performing multiple porphyrin assays?

• A. Refrigeration
• B. Addition of hydrochloric acid
• C. 24-hour urine collection
• D. Use of a brown bottle

Answer: (B)

Preservation and stability of urine specimens for porphyrin assays rely on limiting light exposure, keeping the sample cold, and collecting a representative sample over time. Refrigeration slows degradation and microbial changes that could alter porphyrin levels. A brown bottle protects porphyrins from light, which can cause photo-degradation. A 24-hour collection ensures that the measured amount reflects total excretion rather than a single void’s variability, improving accuracy. Adding hydrochloric acid, on the other hand, changes the urine’s pH and can alter the chemical form or stability of porphyrins, compromising the integrity of the specimen and the assay results.