What laboratory tests are recommended for a patient with electrical injury, noted numbness, and no external lesions?

Laboratory Testing for Electrical Injury with Numbness and No External Lesions

Order a comprehensive metabolic panel, complete blood count, creatine kinase with serial measurements, cardiac troponin, urinalysis for myoglobin, and obtain an ECG immediately—the absence of external burns does not exclude life-threatening internal injury, and numbness indicates potential nerve damage requiring urgent evaluation. 1, 2

Essential Laboratory Tests

Immediate Priority Labs

• Creatine kinase (CK) must be measured immediately and serially every 6-8 hours for at least 24 hours to detect rhabdomyolysis, as muscle damage from electrical current can occur without visible external injury 1, 2

• Cardiac troponin should be obtained to assess for myocardial injury, as electrical current can cause direct cardiac damage even in the absence of chest burns 2

• Complete blood count (CBC) is essential to evaluate for leukocytosis (indicating tissue injury), thrombocytopenia (suggesting disseminated intravascular coagulation), and baseline hemoglobin 1

• Comprehensive metabolic panel including sodium, potassium, chloride, calcium, magnesium, creatinine, and blood urea nitrogen to detect electrolyte abnormalities and renal dysfunction from myoglobin precipitation 1, 2

• Urinalysis with myoglobin testing is critical to identify myoglobinuria, which appears as dark or tea-colored urine and indicates rhabdomyolysis requiring aggressive fluid resuscitation 1

Additional Essential Tests

• Serum lactate and arterial blood gas should be obtained to assess for metabolic acidosis, which indicates significant tissue injury and poor perfusion 1

• Liver function tests (AST, ALT, bilirubin) may reveal hepatic injury from electrical current or secondary to shock 1

• Coagulation studies (PT, PTT, fibrinogen, D-dimer) are necessary to screen for disseminated intravascular coagulation, which can complicate severe electrical injuries 1

Critical Clinical Context

Why External Appearance is Misleading

• The absence of external lesions or visible burns does not rule out severe internal injury—electrical current follows the path of least resistance through nerves, blood vessels, and muscles, causing deep tissue damage invisible on surface examination 1, 2

• Numbness specifically indicates peripheral nerve injury, which occurs in electrical trauma and may represent either direct electrical nerve damage or secondary injury from compartment syndrome or vascular compromise 1, 3

Cardiac Monitoring Requirements

• 12-lead ECG must be obtained immediately and the patient requires continuous cardiac monitoring for at least 24 hours, as delayed arrhythmias can occur even with normal initial ECG and low-voltage exposure 2

• Patients with any ECG abnormality, loss of consciousness, cardiac symptoms, or high-voltage exposure require intensive care monitoring for 24-48 hours minimum 2

Laboratory Monitoring Algorithm

First 24 Hours

• CK measurements every 6-8 hours—rising CK indicates ongoing muscle breakdown and increased risk of acute kidney injury from myoglobin 1

• Repeat metabolic panel every 12 hours to monitor potassium (hyperkalemia from muscle breakdown), calcium (hypocalcemia from muscle injury), and creatinine (acute kidney injury) 1

• Urine output monitoring with target >1-2 mL/kg/hour if myoglobinuria present—inadequate urine output with elevated CK requires aggressive IV fluid resuscitation 1

Beyond 24 Hours

• Continue CK monitoring until levels plateau or decline, typically 48-72 hours in uncomplicated cases 1

• Repeat troponin at 6-12 hours if initial value elevated or if new cardiac symptoms develop 2

Common Pitfalls to Avoid

• Never discharge a patient with numbness after electrical injury without complete laboratory evaluation—peripheral nerve symptoms indicate significant current passage through the body and warrant full workup 1, 3

• Do not rely on normal initial CK—muscle enzyme elevation may be delayed 6-12 hours after injury, requiring serial measurements 1

• Avoid assuming low-voltage injury is benign—even household current (110-120V) can cause serious internal injury, arrhythmias, and neurological complications 2

• Do not miss compartment syndrome—numbness combined with pain, pallor, or pulselessness requires immediate surgical consultation for fasciotomy consideration, but laboratory tests should not delay this evaluation 1

Neurological Injury Considerations

• Numbness after electrical injury may represent direct nerve damage (usually transient with expected recovery over 6-12 months), spinal cord injury (requiring MRI evaluation), or peripheral nerve injury from thermal/mechanical trauma 4, 5, 3

• Central motor conduction time testing and nerve conduction studies may help characterize nerve injury but should not delay initial stabilization and laboratory evaluation 4

• Long-term neurological sequelae can develop months to years after electrical injury, requiring extended follow-up even if initial evaluation is reassuring 5