What is the appropriate workup for hypokalemia (low potassium levels)?

From the Guidelines

The workup for hypokalemia should begin with a thorough history and physical examination, followed by laboratory testing to confirm the diagnosis and determine the underlying cause, as hypokalemia can increase the risk of ventricular tachycardia and ventricular fibrillation, especially in patients with cardiac disease 1. The initial step in evaluating hypokalemia is to assess the patient's clinical presentation, including symptoms such as muscle weakness, fatigue, and palpitations.

• A thorough history should include questions about medication use, particularly diuretics, which can increase the risk of hypokalemia 1.
• Physical examination should focus on signs of cardiac disease, such as arrhythmias, and signs of muscle weakness. Initial laboratory tests should include:
• Serum potassium
• Serum creatinine
• Blood urea nitrogen
• Serum magnesium
• Complete metabolic panel A 24-hour urine collection for potassium, sodium, chloride, and creatinine can help distinguish between renal and non-renal causes of potassium loss.
• Electrocardiogram (ECG) should be performed to assess for cardiac manifestations of hypokalemia, such as U waves, flattened T waves, or ST-segment depression. Additional testing may include:
• Measurement of serum renin and aldosterone levels, especially if hypertension is present, to evaluate for primary hyperaldosteronism
• Arterial blood gas analysis to identify acid-base disturbances that may contribute to potassium shifts
• Diuretic screen in urine if diuretic use is suspected as the cause For patients with unexplained hypokalemia, evaluation for surreptitious vomiting or laxative abuse should be considered. Imaging studies such as adrenal CT scan may be necessary if endocrine causes are suspected. The workup should be tailored to the clinical presentation, with the goal of identifying the underlying cause to guide appropriate treatment and prevent recurrence, as patients with heart failure should be monitored carefully for changes in serum potassium, and every effort should be made to prevent the occurrence of either hypokalemia or hyperkalemia, both of which may adversely affect cardiac excitability and conduction and may lead to sudden death 1.

From the FDA Drug Label

For the treatment of patients with hypokalemia with or without metabolic alkalosis, in digitalis intoxication, and in patients with hypokalemic familial periodic paralysis. If hypokalemia is the result of diuretic therapy, consideration should be given to the use of a lower dose of diuretic, which may be sufficient without leading to hypokalemia. Potassium depletion sufficient to cause hypokalemia usually requires the loss of 200 mEq or more of potassium from the total body store.

The workup for hypokalemia should consider the following:

• Checking serum potassium levels periodically
• Evaluating the use of diuretics and considering a lower dose if hypokalemia is a result of diuretic therapy
• Assessing dietary intake of potassium and considering supplementation with potassium-containing foods or potassium salts if necessary
• Identifying underlying causes of hypokalemia, such as digitalis intoxication or hypokalemic familial periodic paralysis 2 2

From the Research

Hypokalemia Workup

The workup for hypokalemia involves a careful evaluation of the patient's history, physical examination, and laboratory tests to determine the underlying cause of the electrolyte deficiency.

• A thorough history should include the use of drugs, medications, and the presence of vomiting or diarrhea 3.
• Physical examination should include orthostatic changes in blood pressure and heart rate 3.
• Laboratory tests should include measurement of urine and plasma electrolytes, as well as urinary potassium excretion to determine if there is inappropriate potassium wasting 4, 3.
• A spot urine test for potassium and creatinine, as well as evaluation of acid-base status, can be used as an initial step in the diagnosis of hypokalemia 5.

Causes of Hypokalemia

Hypokalemia can be caused by various factors, including:

• Inadequate potassium intake or excessive potassium loss 3, 5.
• Gastrointestinal potassium wasting, which can be identifiable by an associated increase in fluid losses via biliary tract or bowel 4.
• Diuretic therapy, which is the most common cause of potassium deficiency 4, 6, 7.
• Abnormalities of the pituitary-adrenal axis, renal disorders, and other drugs 4.
• Primary increase in distal sodium delivery or primary increase in mineralocorticoid level 3.

Evaluation of Urinary Potassium Loss

If urinary potassium loss is identified, the next step is to determine whether the loss is caused by a primary increase in distal delivery of sodium or a primary increase in mineralocorticoid level 3.

• A primary increase in distal delivery should be associated with volume depletion, whereas a primary increase in mineralocorticoid level generally is associated with volume expansion and hypertension 3.
• Measurement of plasma renin activity and plasma aldosterone levels may be useful in patients with a primary increase in mineralocorticoid activity 3.

Complications of Hypokalemia

Hypokalemia can lead to various complications, including:

• Muscle weakness, rhabdomyolysis, cardiac arrhythmias, impaired urinary concentrating ability, and glucose intolerance 3, 6, 7.
• Cardiac arrhythmias, muscle weakness, and rhabdomyolysis can be serious consequences of potassium deficiency 6, 7.
• Diuretic-induced hypokalaemia can be potentially life-threatening and may require reduction of diuretic dose and potassium supplementation 7.