Hyperkalemia diagnostic study of choice

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Diagnostic Study of Choice

Study of choice

[Serum potassium] is the gold standard test for the diagnosis of [hyperkalemia].

There are two methods to determine serum potassium   :

• Flame emission spectrophotometry

• Ion-specific electrode (ISE) potentiometry

ISE potentiometry has two different subtypes: Direct (undiluted) and indirect (diluted).

Direct ISE measures plasma potassium directly from a whole-blood sample and it's not associated with either pseudohyperkalemia.

FES or indirect ISE requires sample dilution before assay and both are associated with pseudohyperkalemia.

Pseudohyperkalemia

Pseudohyperkalemia is defined when serum potassium concentration exceeds that of plasma without any symptoms of hyperkalemia.It usually occurs when potassium moves out of cells during blood specimen collection or during centrifugation of the sample.Other causes are thrombocytosis,leukocytosis and erythrocytosis.To rule out pseudohyperkalemia we need to do the following

*Repeat the blood sample

*Complete blood count to rule out thrombocytosis,erythrocytosis and leukocytosis

*Measurement of plasma potassium and whole blood potassium

Diagnostic results

The finding on performing the diagnostic test that confirms hyperkalemia

*Serum Potassium level more than 5.1 meq/L.

Sequence of Diagnostic Studies

The [serum potassium] must be performed when:

• The patient presented with cardiac arrhythmias,weakness,fatigue and known case of chronic kidney disease as the first step of diagnosis.

The various investigations must be performed in the following order:

• Blood pressure(to look for hypoaldosteronism)
• Complete blood count
• Renal function tests
• Urine potassium,sodium and osmolality
• Metabolic profile(other electrolytes)
• ECG
• Bicarbonate level
• Serum glucose
• Serum Calcium

Depending on the history and results of the above mentioned tests,other tests that can be performed for evaluating the cause of hyperkalemia.

• Digoxin level - If the patient is on a digitalis medication
• Arterial or venous blood gas
• Urinalysis
• Serum cortisol and aldosterone levels
• Serum uric acid and phosphorus assays
• Serum creatinine phosphokinase (CPK) measurements
• Urine myoglobin test