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

How should a blood ammonia test specimen be preserved until testing?

1. At room temperature

2. In a cup of ice water

3. In a refrigerator

4. In an incubator

The correct answer is: In a cup of ice water

For preserving a blood ammonia test specimen until testing, maintaining the sample at a lower temperature is crucial to ensure the stability of ammonia levels in the specimen. When blood is drawn for ammonia testing, it is vital to prevent any potential increase in ammonia concentration due to factors like cellular metabolism. The ideal method for immediate preservation is to place the specimen in a container submerged in a cup of ice water. This helps to rapidly cool the sample, inhibiting enzymatic activities that could lead to false elevations in ammonia levels before the specimen is analyzed. The other options may not provide the appropriate conditions for sample preservation. For instance, storing the specimen at room temperature can lead to increased metabolic processes that may elevate ammonia levels, resulting in inaccurate test results. Similarly, refrigeration could be problematic, as it is not as effective in preventing enzyme activity compared to immediate cooling on ice. Finally, storing the specimen in an incubator would not be advisable, as this would create a warm environment that could significantly impact the accuracy of the ammonia measurement.