Laboratory Evaluation for Suspected Hyperkalemia
Immediately obtain a serum potassium level (basic or comprehensive metabolic panel), ECG, and verify the result is not pseudohyperkalemia from hemolysis or poor phlebotomy technique before initiating treatment. 1, 2
Essential Initial Laboratory Tests
Core Labs (Obtain Immediately)
Serum potassium level via basic or comprehensive metabolic panel to confirm hyperkalemia and classify severity (mild >5.0-<5.5 mEq/L, moderate 5.5-6.0 mEq/L, severe >6.0 mEq/L) 1, 3
Serum creatinine and eGFR to assess renal function, as kidney disease is the most common cause of severe hyperkalemia and impaired renal excretion is the dominant mechanism of sustained hyperkalemia 1, 2
Blood urea nitrogen (BUN) to evaluate for acute kidney injury or worsening chronic kidney disease 1
Serum glucose to detect hyperglycemia, which causes transcellular potassium shifts from intracellular to extracellular space due to hyperosmolarity and insulin deficiency 1, 2
Complete blood count to evaluate for infection/sepsis as a trigger, since all cases of hyperkalemia-induced cardiac arrest in one retrospective study had acute kidney injury present, often from sepsis 1, 2
Additional Critical Labs
Arterial or venous blood gas to assess for concurrent metabolic acidosis (pH <7.35, bicarbonate <22 mEq/L), which directly influences treatment decisions—sodium bicarbonate should ONLY be used when metabolic acidosis is present 1, 2
Serum calcium to detect hypercalcemia, which is critical because non-dialysis CKD patients with hypercalcemia may not manifest the usual ECG abnormalities associated with hyperkalemia, making ECG unreliable in this population 1, 4
Serum magnesium to evaluate electrolyte balance, as for each 1 mEq/L increase in serum magnesium, serum potassium increases by 1.07 mEq/L 1
Urinalysis to assess kidney function and identify underlying renal pathology 1
Verification of True Hyperkalemia
Repeat potassium measurement with proper technique or obtain arterial sample to exclude pseudohyperkalemia from hemolysis, repeated fist clenching, or poor phlebotomy technique before initiating treatment 1, 2
Pseudohyperkalemia must be ruled out first, as it can result from improper blood sampling and does not require treatment 1, 2
Electrocardiogram (Mandatory)
Obtain immediate 12-lead ECG to detect life-threatening changes (peaked T waves, flattened P waves, prolonged PR interval, widened QRS complexes) that indicate urgent treatment regardless of potassium level 1, 2
Critical caveat: ECG findings are highly variable and less sensitive than laboratory tests—a normal ECG does NOT rule out severe hyperkalemia, particularly in non-dialysis CKD patients with hypercalcemia 1, 4, 5
Emergency physicians have a mean sensitivity of only 0.19 for detecting hyperkalemia on ECG, though specificity is high at 0.97, meaning ECG is not reliable to rule out hyperkalemia but can be used as a "rule-in" test 5
Medication Review (Essential Component)
- Systematically review all medications that may contribute to hyperkalemia: RAAS inhibitors (ACE inhibitors, ARBs, mineralocorticoid antagonists), NSAIDs, potassium-sparing diuretics, trimethoprim, heparin, beta-blockers, potassium supplements, and salt substitutes 1, 2
Common Pitfalls to Avoid
Do not rely solely on ECG findings—they are highly variable and less sensitive than laboratory tests, with some patients having severe hyperkalemia (K >8.0 mEq/L) and completely normal ECGs 1, 4, 5
Do not delay treatment while waiting for repeat lab confirmation if ECG changes are present—ECG changes indicate urgent need regardless of the exact potassium value 1
Do not overlook hypercalcemia in CKD patients—this combination can mask typical ECG findings of hyperkalemia, creating a false sense of security 4
Always verify the result is not pseudohyperkalemia before initiating aggressive treatment, as hemolysis or improper sampling technique can falsely elevate potassium levels 1, 2