Measuring serum ammonia levels has potential preanalytical errors. Which option is incorrect?

Measuring serum ammonia levels has potential preanalytical errors. Which option is incorrect?

• A. After phlebotomy, the blood should be immediately placed on ice.
• B. The blood should be collected in a red clot tube without anticoagulant.
• C. Hemolyzed samples should be rejected as this interferes by falsely increasing ammonia levels.
• D. Lipemia may also interfere with plasma ammonia measurements.

Answer: (B)

Measuring ammonia levels is highly sensitive to preanalytical handling because ammonia can be produced by blood cells after collection. To get an accurate result, the sample must be kept cold and processed quickly to minimize in vitro production. Using a red top tube without anticoagulant means the blood will clot. During clot formation and ongoing cellular metabolism, ammonia can be released into the serum, causing falsely elevated results. This makes collecting in a red clot tube without anticoagulant an inappropriate method for accurate ammonia measurement. In contrast, placing the blood on ice and using an anticoagulated tube to obtain plasma helps preserve the true ammonia level. Hemolyzed samples release intracellular ammonia and falsely raise values, and lipemia can interfere with measurements, so those conditions are also problematic.

Measuring ammonia levels is highly sensitive to preanalytical handling because ammonia can be produced by blood cells after collection. To get an accurate result, the sample must be kept cold and processed quickly to minimize in vitro production. Using a red top tube without anticoagulant means the blood will clot. During clot formation and ongoing cellular metabolism, ammonia can be released into the serum, causing falsely elevated results. This makes collecting in a red clot tube without anticoagulant an inappropriate method for accurate ammonia measurement. In contrast, placing the blood on ice and using an anticoagulated tube to obtain plasma helps preserve the true ammonia level. Hemolyzed samples release intracellular ammonia and falsely raise values, and lipemia can interfere with measurements, so those conditions are also problematic.