Pediatric Hyperkalemia Workup

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

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.

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Electrocardiography

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.
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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).

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