Acid-base and Electrolyte Cases Session (April 13, 2018)
Speaker: Michael Emmett
Sodium levels are influenced by the effect of hyperviscosity and the ion selective electrode method of measurement. Flame photometer is affected by displacement errors leading to Na errors. When direct poteniometry (ISE) is used, it is unaffected by solids displacements issues and hence no errors in Na measurements. If the plasma is grossly lipemic (TG), suspect displacement errors leading to low Na levels in serum. Another less common displacement error-prone state is dysproteinemias. This is ALMOST NEVER caused by hypercholesterolemia.
Pseudohyperkalemia can be a result of fist-clinching, tourniquet-related concerns, or K-rich IV fluid contamination but can also result in collection tube-related issues and a cell release problem.
A RBC release of K is due to hemolysis and RBC membrane defects. Platelet release of K is due to clotting and inhibition of Na-K ATPase. The WBC release of K is due to fragility and clotting with heparin in some cases.
The most common electrolyte disorder encountered in chronic lymphocytic leukemia (CLL) patients is pseudohyperkalemia. In addition, myeloproliferative disorders and thrombocytosis can also lead to pseudohyperkalemia. Thrombocytosis (platelet count > 1000 × 109/L) can also lead to pseudohyperkalemia. Elevation of the blood platelet count by 1000 × 109/L can lead to an increase of 0.2 mmol/L in plasma potassium and 0.7 mmol/L in serum potassium. As a result, the potassium concentration is generally higher in serum compared with plasma from platelets during clotting. Similarly, elevated potassium levels have been described in leukocytosis as well. An artifactually elevated serum potassium level or spurious hyperkalemia was first described with extreme leukocytosis (> 600 × 109/L) and several case reports thereafter.
While in elevated platelet levels, serum and plasma levels can differentiate pseudohyperkalemia, elevated white cell–related pseudohyperkalemia might not be as straightforward to distinguish. Although not common, another interesting electrolyte disorder noted in CLL patients is reverse pseudohyperkalemia, where plasma potassium is noted to be higher than serum potassium. The mechanism is not well understood but may be due to an increase in sensitivity to heparin-mediated cell membrane damage during processing and centrifugation in a hematologic malignancy and mechanical stressors.
It is tough to figure out if the K is really elevated in CLL. A recent review summarizes the potential mechanism on how to avoid pitfalls in treatment of pseudohyperkalemia in CLL.