In cases of suspected pseudohyperkalemia due to platelet release, which specimen provides the most accurate potassium measurement?

• A. Repeat the original serum test
• B. Freshly drawn serum
• C. Heparinized plasma
• D. Atomic absorption spectrometry

Answer: (C)

When platelets release potassium during clotting, serum potassium can appear falsely high—a situation called pseudohyperkalemia. To avoid this artifact, the measurement should come from a specimen that doesn’t clot, so potassium isn’t released from platelets. A heparinized plasma sample accomplishes this by preventing clot formation, yielding a potassium value that more accurately reflects the true circulating level. Freshly drawn serum would still clot and show the artifact, and repeating the serum test would reproduce the same misleading result. Atomic absorption spectrometry is a measurement method, not a specimen type, so it doesn’t address the issue.