Erroneous ammonia levels can be eliminated by all of the following except:

• A. Ensuring water and reagents are ammonia-free
• B. Separating plasma from cells and testing as soon as possible
• C. Drawing the specimen in a pre-chilled tube and placing on ice
• D. Storing the specimen protected from light until analysis

Answer: (D)

The key idea here is that ammonia measurements are highly affected by what happens after blood is drawn. Ammonia can be produced in the sample by remaining blood cells or by contaminants, leading to falsely elevated results if the sample is not handled promptly and properly.

Using water and reagents that are ammonia-free prevents adding external ammonium into the assay environment, which is essential to avoid contamination-driven falsely high readings. Separating plasma from cells as soon as possible stops leukocytes and platelets from continuing to generate ammonia, so the measured level reflects the patient’s true value rather than in vitro production. Drawing the specimen into a pre-chilled tube and placing it on ice further slows cellular and enzymatic activity, reducing the chance of in vitro ammonia production before analysis.

Storing the specimen protected from light does not have a meaningful impact on ammonia stability, because ammonia is not notably affected by light exposure. Therefore protecting from light does not help eliminate erroneous ammonia levels, making it the exception among these measures.