Unit Converter
Potassium (K)
(Major Intracellular Cation - Critical for Nerve, Muscle, Cardiac Function & Acid–Base Balance)
Synonyms
- Potassium
- Serum potassium
- K⁺
- Plasma potassium
- Extracellular potassium
Units of Measurement
- mmol/L
- mEq/L
Equivalency
1 mmol/L=1 mEq/L1\ \text{mmol/L} = 1\ \text{mEq/L}1 mmol/L=1 mEq/L
Potassium has a valence of +1, so mmol = mEq.
Description
Potassium is the primary intracellular cation with key roles in:
- Resting membrane potential
- Muscle contraction
- Cardiac conduction
- Nerve impulse transmission
- Acid–base balance
- Cellular metabolism
Only 2% of total body potassium is in the extracellular fluid, making serum potassium very sensitive to:
- Diet
- Renal excretion
- Hormonal control
- Acid–base status
- Drugs
Kidneys regulate potassium primarily via:
- Aldosterone
- Distal nephron secretion
- Acid–base changes
Physiological Role
- Maintains electrical gradients across cell membranes
- Essential for cardiac rhythm stability
- Required for muscle contraction
- Regulates insulin release
- Buffers acid–base disorders
Potassium balance is tightly controlled. Small variations can cause dangerous arrhythmias.
Clinical Significance
HIGH Potassium (Hyperkalemia)
(K⁺ > 5.0 mmol/L)
A medical emergency when severe.
Major Causes
1. Renal Failure
Most common cause.
2. Medications
- ACE inhibitors
- ARBs
- Potassium-sparing diuretics (spironolactone)
- NSAIDs
- Calcineurin inhibitors
3. Cellular Shift (Out of Cells)
- Metabolic acidosis
- DKA
- Hemolysis
- Rhabdomyolysis
- Tumor lysis syndrome
4. Endocrine
- Addison disease (low aldosterone)
- Hypoaldosteronism
5. Pseudohyperkalemia
False elevation due to:
- Hemolysis
- Prolonged tourniquet
- Thrombocytosis (>1000 ×10⁹/L)
- Leukemia (WBC >100 ×10⁹/L)
Symptoms
- Palpitations
- Muscle weakness
- Paralysis
- Cardiac arrhythmias
- Cardiac arrest (K⁺ >7.0 mmol/L)
LOW Potassium (Hypokalemia)
(K⁺ < 3.5 mmol/L)
Major Causes
1. Gastrointestinal Losses
- Vomiting
- Diarrhea
- NG suction
2. Renal Losses
- Diuretics (most common cause)
- Hyperaldosteronism
- Cushing syndrome
- Renal tubular acidosis
3. Cellular Shift (Into Cells)
- Alkalosis
- Insulin therapy
- β-agonists (salbutamol)
- Refeeding syndrome
4. Poor Intake
Malnutrition, alcoholism.
Symptoms
- Muscle cramps
- Weakness
- Constipation
- Paralysis
- Ventricular arrhythmias
- U waves on ECG
Reference Intervals
(Tietz 8E + Mayo + ARUP)
Adults
- 3.5 – 5.0 mmol/L
Children
- Slightly higher upper range:
3.8 – 5.5 mmol/L
Critical Values
- < 2.5 mmol/L → risk of paralysis, respiratory failure
- > 6.5 mmol/L → risk of ventricular fibrillation/asystole
Diagnostic Uses
1. Emergency Medicine
Hyperkalemia & hypokalemia management.
2. Renal Disease
Monitoring CKD, AKI, dialysis patients.
3. Acid–Base Disorders
Potassium shifts help interpret metabolic states.
4. Cardiac Disorders
Arrhythmia risk assessment.
5. Endocrine Disorders
Aldosterone-related diseases.
6. Diuretic Therapy Monitoring
7. DKA Management
Potassium must be monitored every 1–2 hours.
Analytical Notes
- Hemolysis falsely increases K⁺ (most important pre-analytical issue)
- Plasma potassium is slightly lower than serum
- Avoid fist clenching & prolonged tourniquet
- Store samples promptly
- High platelet or WBC count → pseudohyperkalemia
Clinical Pearls
- Hyperkalemia is more dangerous than hypokalemia (cardiac arrest risk).
- Diuretics → low K⁺; ACEI/ARB → high K⁺.
- Every 0.3 mmol/L drop represents ~100 mmol total body potassium deficit.
- In DKA, potassium may be high initially but total body K⁺ is severely depleted.
- Treat pseudohyperkalemia by repeating sample (heparinized tube).
Interesting Fact
Potassium was first isolated from potash (burnt wood ash) - hence “potassium.”
Its symbol K comes from kalium, the Latin name.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Electrolytes
- Mayo Clinic Laboratories - Potassium
- ARUP Consult - Electrolyte Testing
- AHA - Hyperkalemia Management Guidelines
- KDIGO - CKD Electrolyte Abnormalities
- MedlinePlus / NIH - Potassium Blood Test