Hypokalemia

1. See Also
   1. Serum Potassium
   2. Hypokalemia due to Renal Potassium Loss
   3. Hypokalemia due to Extrarenal Potassium Loss
   4. Hypokalemia due to Transcellular Potassium Shift
   5. Familial Periodic Paralysis
   6. Potassium Replacement
   7. Dietary Potassium
2. Pathophysiology
   1. Approximate Total body Potassium = 55 meq/kg
   2. Serum Potassium decreased 0.3 mEq/L: 100 mEq K+ total body deficit
   3. Serum Potassium decreased 1 mEq/L: 350 mEq K+ total body deficit
   4. Serum Potassium less than 2 mEq/L: 1000 mEq K+ total body deficit
3. Causes
   1. Hypokalemia due to Transcellular Potassium Shift
      1. See Transcellular Potassium Shift
      2. Medications (Beta-agonists, Insulin excess)
      3. Metabolic Alkalosis
      4. Hypokalemic Periodic Paralysis
      5. Thyrotoxicosis
   2. Hypokalemia due to Renal Potassium Loss
      1. See Renal Potassium Loss (Hyperkaluria)
      2. Hypertension: Obtain Plasma Renin and Aldosterone
         1. Renin high
            1. Renovascular disease, renin secreting tumor or Malignant Hypertension
         2. Renin normal
            1. Liddle's Syndrome
         3. Renin low
            1. Aldosterone High: Primary Hyperaldosteronism, Bilateral adrenal hyperplasia
            2. Aldosterone Low: Congenital Adrenal Hyperplasia, Cushing's Syndrome, Ectopic ACTH
      3. Normotensive: Obtain serum bicarbonate and Urine Chloride
         1. Serum Bicarbonate Low
            1. Renal Tubular Acidosis
         2. Serum Bicarbonate High
            1. Urine Chloride Low: Vomiting
            2. Urine Chloride High: Barter's Syndrome, Normotensive primary Hyperaldosteronism, Diuretic use
   3. Hypokalemia due to Extrarenal Potassium Loss
      1. See Extrarenal Potassium Loss
      2. Normal Acid-Base Status or Metabolic Alkalosis
         1. Gastrointestinal or skin losses, Hypomagnesemia, Penicillin or Aminoglycosides, Acute Leukemia
      3. Metabolic Acidosis
         1. Diabetic Ketoacidosis, Diarrhea, Laxatives
   4. Other causes
      1. Inadequate Potassium intake (typically in hospitalized patients)
         1. Total Parenteral Nutrition
         2. Anorexia or Starvation
         3. Dementia
      2. Pseudohypokalemia
         1. Delayed lab analysis of sample
         2. Severe Leukocytosis (>75,000/mm3)
4. Findings: Symptoms and Signs (when Serum Potassium < 2.5)
   1. General
      1. Malaise
      2. Fatigue
   2. Neurologic
      1. Weakness
      2. Decreased Deep Tendon Reflexes
      3. Paresthesia
      4. Cramps
      5. Restless Legs Syndrome
      6. Rhabdomyolysis
      7. Paralysis
   3. Gastrointestinal
      1. Constipation
      2. Ileus
      3. Exacerbated Hepatic Encephalopathy
   4. Cardiovascular
      1. Orthostatic Hypotension
      2. Hypertension
      3. Arrhythmias (especially with Digoxin use)
   5. Renal
      1. Metabolic Alkalosis
      2. Polyuria, Polydipsia
      3. Decreased GFR
      4. Glucose Intolerance
5. Labs
   1. Serum Potassium <3.6 mEq/L
   2. Serum Magnesium
      1. Confirm no Hypomagnesemia (Hypokalemia cause)
   3. Complete Blood Count
      1. Confirm no severe Leukocytosis (pseudohypokalemia)
   4. Urine Potassium-to-Creatinine ratio
      1. Ratio <=1.5 mEq/mmol
         1. Hypokalemia due to Extrarenal Potassium Loss
      2. Ratio >1.5 mEq/mmol
         1. Hypokalemia due to Renal Potassium Loss
   5. 24 hour Urine Potassium and Urine Sodium
      1. Most accurate evaluation of Urine Potassium excretion
      2. However, Urine Potassium-to-Creatinine ratio is typically obtained instead
      3. Sample should have total Urine Sodium > 100 meq
      4. Urine Potassium <20-30 meq/day
         1. See Extrarenal Potassium Loss
      5. Urine Potassium >20-30 meq/day
         1. See Renal Potassium Loss
6. Diagnostics: Electrocardiogram
   1. Early changes
      1. T Waves decreased amplitude to flattened
   2. Later changes
      1. Prominent U Waves
      2. ST depression
      3. T Wave inversion
      4. PR prolongation (first degree AV Block)
   3. Arrhythmias associated with Hypokalemia
      1. Sinus Bradycardia
      2. Ventricular Tachycardia or Ventricular Fibrillation
      3. Torsade de pointes
7. Management
   1. See Potassium Replacement
      1. Goal Serum Potassium >3.5 mEq/L (>4.0 in CAD, CHF)
      2. Avoid rebound Hyperkalemia (over-shooting replacement)
      3. Dietary Potassium (Potassium phosphate) is less effective replacement than KCl
         1. Most Hypokalemia is associated with concurrent chloride depletion
   2. Replace Serum Magnesium if Hypomagnesemia
      1. Consider empiric Magnesium Replacement in refractory Hypokalemia
   3. Emergent replacement indicated for serious findings or risks
      1. EKG changes (see above)
      2. Severe Hypokalemia (Serum Potassium <2.5 mEq/L)
      3. Rapid onset Hypokalemia
      4. Serious comorbidity (heart disease, Cirrhosis)
   4. Consider pseudohypokalemia
      1. Consider re-drawing lab for confirmation if delayed analysis
      2. Confirm no severe Leukocytosis (WBC >75,000/mm3)
   5. Consider Transcellular Potassium Shift
      1. See Transcellular Potassium Shift
      2. Hypokalemia from transcellular shift is typically transient
   6. Obtain Urine Potassium-to-Creatinine ratio
      1. Ratio <=1.5 mEq/mmol: Hypokalemia due to Extrarenal Potassium Loss
         1. Manage underlying losses
      2. Ratio >1.5 mEq/mmol: Hypokalemia due to Renal Potassium Loss
         1. Elevated Blood Pressure or hypervolemia (mineralcorticoid excess)
            1. Hyperaldosteronism
            2. Renal Artery Stenosis
            3. Cushing Syndrome
            4. Congenital Adrenal Hyperplasia
         2. Metabolic Acidosis
            1. Type I and II Renal Tubular Acidosis
         3. Metabolic Alkalosis
            1. Diuretics
            2. Renal Tubular transport disorders (e.g. Bartter Syndrome)
8. References
   1. Viera (2015) Am Fam Physician 92(6): 487-95 [PubMed]