Laboratory Tests for Checking Potassium Levels

Serum potassium measurement is the standard laboratory test used to check potassium levels in the body. 1, 2

Primary Test for Potassium Assessment

Serum potassium is measured as part of basic laboratory tests, which typically include blood count, INR (in patients on vitamin K antagonists), serum creatinine, sodium, potassium, liver function tests (ASAT/ALAT), bilirubin, and natriuretic peptides 1
Potassium levels are commonly measured as part of a comprehensive metabolic panel or basic metabolic panel 1
The normal range for serum potassium is typically 3.5-5.0 mEq/L, with values below 3.5 mEq/L classified as hypokalemia and above 5.0 mEq/L as hyperkalemia 3

Blood samples should be collected without excessive fist clenching or prolonged tourniquet use, as these can falsely elevate potassium levels 1
When blood is drawn for analysis of plasma potassium, it's important to recognize that artifactual elevations can occur after improper venipuncture technique or as a result of in-vitro hemolysis of the sample 2
Elevated potassium levels should be verified immediately with a second sample to rule out fictitious hyperkalemia from hemolysis during phlebotomy 1
Plasma potassium concentrations are usually 0.1-0.4 mEq/L lower than serum levels, which is caused by the release of potassium from platelets during coagulation 1

For patients on medications affecting potassium levels (such as diuretics, ACE inhibitors, or aldosterone antagonists), regular monitoring is essential 1
After initiating medications that affect potassium levels, such as aldosterone receptor antagonists, potassium levels should be checked within 3-7 days and at least monthly for the first 3 months 1
For patients with heart failure on potassium-affecting medications, potassium should be monitored every 3-6 months during routine follow-up 1
In patients with chronic kidney disease starting renin-angiotensin-aldosterone system inhibitors, serum potassium should be measured within 1 week of starting or dose escalation 1

When interpreting serum potassium levels, physicians should consider that acute alkalosis can produce hypokalemia even with normal total body potassium, while acute acidosis can increase serum potassium into the normal range despite reduced total body potassium 2
Both hypokalemia and hyperkalemia are associated with increased mortality risk, with the lowest risk observed at serum potassium levels of 4.0-4.5 mmol/L 4
Potassium levels outside the 4.0-5.0 mmol/L range are associated with increased mortality risk, with a U-shaped correlation between potassium levels and mortality 5

In patients with heart failure, potassium levels should be maintained in the 4.0-5.0 mEq/L range to prevent adverse cardiac events 5
For patients receiving aldosterone receptor antagonists, potassium should be less than 5.0 mEq/L before initiation of therapy 1
In patients with tumor lysis syndrome, potassium levels should be monitored every 4-6 hours after the initial administration of chemotherapy 1
Hypomagnesemia should be assessed when hypokalemia is present, as it can make hypokalemia resistant to correction 5

Failing to verify elevated potassium with a repeat sample when hemolysis is suspected 1
Not considering the timing of sample collection, as circadian rhythm can influence potassium homeostasis 1
Overlooking the need to monitor both potassium and renal function when initiating medications that affect potassium levels 1
Neglecting to monitor magnesium levels when dealing with persistent hypokalemia 5