Variable Potassium Concentrations: Which Is Right and Which Is Wrong?

Area of Science:

• Hematology
• Clinical Chemistry

Background:

• Reverse pseudohyperkalemia is an in vitro artifact causing falsely elevated plasma potassium.
• It is associated with extreme leukocytosis, often seen in hematologic malignancies.
• Tumor lysis syndrome (TLS) is a clinical condition with in vivo cell lysis, leading to electrolyte abnormalities.

Observation:

• A 66-year-old man with stage IV mantle-cell lymphoma presented with leukocytosis (>100,000 cells/mm³).
• Initial presentation included elevated potassium, uric acid, and phosphorus, leading to a suspected diagnosis of TLS.
• The patient exhibited persistent high whole blood potassium levels post-hemodialysis, contrasting with decreased serum potassium.

Findings:

• The patient was accurately diagnosed with reverse pseudohyperkalemia, not TLS.
• Accurate potassium measurements were achieved using serum specimens, distinguishing artifact from true hyperkalemia.
• This case underscores the diagnostic challenge posed by reverse pseudohyperkalemia in leukemic patients.

Implications:

• Accurate differentiation between reverse pseudohyperkalemia and TLS is critical for appropriate patient management.
• Laboratory protocols should consider potential for pseudohyperkalemia in leukocytosis.
• Correct potassium measurement techniques are essential for avoiding misdiagnosis and inappropriate treatment in hematologic disorders.