Which Potassium Do You Believe?

A patient presented to the Emergency Department at the St. Paul’s Hospital. Initial blood was collected by phlebotomy staff (one poke) at 6:55 am in the morning and the specimen was received in the lab at 7:11 am.

Venous blood gases: Potassium  7.3 mmol/L
Plasma Lytes: Potassium  3.3 mmol/L

Emergency phoned the lab about these discrepant potassium results. What is going on?! The venous gas specimen was centrifuged and appeared hemolysed (3+), while the plasma sample had no evidence of hemolysis.

The phlebotomist indicated there was no problem with the collection. Repeat testing was initiated an hour later.

Venous blood gases: Potassium  6.4 mmol/L
Plasma Lytes: Potassium  3.6 mmol/L

The venous gas specimen was centrifuged and appeared hemolysed (3+).

Because the venous gas specimens were transported on ice and the other tubes of blood collected were sent at room temperature, the biochemist discussed the possibility of a red cell cold agglutinin with the ER physicians. The ER physicians requested evaluation for a cold agglutinin (the EDTA tube collected for early hematology was used for this analysis). Lab staff performed the screen and it was 4+ for cold agglutinin.  ER physicians were advised to believe the lower potassium results and to avoid sending further specimens on ice for this patient.

 

Lyon-small

-Dr. Andrew Lyon, PhD, FCACB, DABCC is a clinical chemist and clinical toxicologist. He is the current past-president of the Canadian Society of Clinical Chemists. He is currently Division Head of Clinical Biochemistry of the Saskatoon Health Region and teaches general pathology residents as a clinical associate professor of Pathology and Laboratory Medicine at the University of Saskatchewan.

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