Laboratory Studies
Potassium level
The relationship between the serum potassium level and symptoms is not consistent. For example, patients with a chronically elevated potassium level may be asymptomatic at much higher levels than other patients. The rapidity of change in the potassium level influences the symptoms observed at various potassium levels.
BUN and creatinine level
For evaluation of renal status
Calcium level
If patient has renal failure (because hypocalcemia can exacerbate cardiac rhythm disturbances)
Glucose level
In patients with diabetes mellitus
Digoxin level
If patient is on a digitalis medication
Arterial or venous blood gas
If acidosis is suspected
Urinalysis
If signs of renal insufficiency without an already known cause are present (to look for evidence of glomerulonephritis)
Other Tests
Continuous cardiac monitoring
Indicated for evaluation of rhythm disturbances
ECG
ECG is essential and may be instrumental in diagnosing hyperkalemia in the appropriate clinical setting. ECG changes have a sequential progression of effects, which roughly correlate with the potassium level.
ECG findings may be observed as follows:
-
Early changes of hyperkalemia include peaked T waves, shortened QT interval, and ST-segment depression.
-
These changes are followed by bundle-branch blocks causing a widening of the QRS complex, increases in the PR interval, and decreased amplitude of the P wave (see the images below).
-
These changes reverse with appropriate treatment (see the image below).
ECG of a patient with pretreatment potassium level of 7.8 mEq/L and widened QRS complexes after receiving 1 ampule of calcium chloride. Notice narrowing of QRS complexes and reduction of T waves.
-
Without treatment, the P wave eventually disappears and the QRS morphology widens to resemble a sine wave. Ventricular fibrillation or asystole follows.
-
ECG findings generally correlate with the potassium level, but potentially life-threatening arrhythmias can occur without distinct ECG changes at almost any level of hyperkalemia.
Cortisol and aldosterone levels
To check for mineralocorticoid deficiency when other causes are eliminated
-
Widened QRS complexes in hyperkalemia.
-
Widened QRS complexes in a patient whose serum potassium level was 7.8 mEq/L.
-
ECG of a patient with pretreatment potassium level of 7.8 mEq/L and widened QRS complexes after receiving 1 ampule of calcium chloride. Notice narrowing of QRS complexes and reduction of T waves.
