Pediatric Hyperkalemia Workup

Updated: Jan 08, 2016
  • Author: Michael J Verive, MD, FAAP; Chief Editor: Timothy E Corden, MD  more...
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Laboratory Studies

Laboratory studies depend on the etiology of hyperkalemia but may include the following:

  • Serum electrolyte tests
  • Serum BUN and creatinine tests
  • Urinalysis (UA)

Depending on the etiology or on clinical suspicion, other studies to consider include the following:

  • Arterial or free-flowing venous blood gas sampling (for acid-base disorders): Capillary blood gas sampling should not routinely be used to evaluate for hyperkalemia due to significant risks of factitious hyperkalemia.
  • Serum uric acid and phosphorous tests (for tumor lysis syndrome)
  • Serum creatinine phosphokinase (CPK) and calcium measurements (for rhabdomyolysis)
  • Urine myoglobin test (for crush injury or rhabdomyolysis; suspect if UA reveals blood in the urine but no RBCs are seen on urine microscopy)
  • Specific drug level tests for suspected toxicity (digoxin)
  • CBC count (for thrombocytosis, leukocytosis, or malignancy)
  • Urine electrolyte tests, including potassium and osmolality (osm) tests
  • Plasma osm test

When the etiology of hyperkalemia remains unclear, calculation of the transtubular potassium gradient (TTKG) using the following formula may be useful: TTKG = (K+ urine X Osm plasma)/(K+ plasma X Osm urine)

The normal TTKG varies from 5-15. In the setting of hyperkalemia with normal renal excretion of potassium, the TTKG should be greater than 10. A TTKG of less than 8 in the setting of hyperkalemia implies inadequate potassium excretion, which is usually secondary to aldosterone deficiency or unresponsiveness. Checking a serum aldosterone level may be helpful.



An ECG is essential in all children in whom hyperkalemia is suspected. ECG reveals the sequence of changes as follows:

  • Serum K + 5.5-6.5 mEq/L - Tall, peaked T waves with narrow base, best seen in precordial leads (as is shown in the image below)
    Peaked T waves. Peaked T waves.
  • Serum K + 6.5-8.0 mEq/L - Peaked T waves, prolonged PR interval, decreased or disappearing P wave, widening of QRS, amplified R wave
  • Serum K + greater than 8.0 mEq/L - Absence of P wave; progressive QRS widening, intraventricular/fascicular/bundle branch blocks; progressive widening of QRS, eventually merging with the T wave just before cardiac arrest, forming the sine wave pattern (as is shown in the image below)
    Sinusoidal wave. Sinusoidal wave.

Imaging Studies

Imaging studies are not generally indicated, except to assess the primary disease state (eg, excluding obstructive uropathy as a cause for acute renal failure).