What laboratory studies should be ordered to evaluate a patient with hypotension?

Laboratory Studies for Hypotension Evaluation

Order a comprehensive metabolic panel, complete blood count, arterial blood gas with lactate, ECG, and bedside echocardiography immediately to identify the underlying cause and assess end-organ perfusion. 1

Essential Initial Laboratory Tests

Immediate Blood Work (Priority)

• Arterial blood gas and serum lactate to assess tissue perfusion and shock severity 1
• Complete blood count to evaluate for anemia or infection 1
• Comprehensive metabolic panel including sodium, potassium, creatinine, and blood urea nitrogen 1
• Estimated glomerular filtration rate (eGFR) to assess renal function 2

Additional Core Laboratory Studies

• Troponin-T, CK, CK-MB if chest pain or suspected cardiac ischemia 2
• Lactate dehydrogenase (LDH) and haptoglobin to evaluate for thrombotic microangiopathy in malignant hypertension presenting with rebound hypotension 2
• Liver function tests as part of comprehensive assessment 2
• Fasting glucose and lipid profile when available 2

Diagnostic Examinations Beyond Labs

Mandatory Bedside Tests

• 12-lead ECG to identify bradycardia, tachyarrhythmias, acute myocardial infarction, or ischemia 1, 2
• Bedside echocardiography urgently to evaluate left ventricular function, mechanical complications, and volume status 1
• Pulse oximetry or arterial blood gas to assess oxygenation 2

Urine Studies

• Quantitative urinalysis for protein 2
• Urine sediment for erythrocytes, leukocytes, cylinders, and casts 2
• Dipstick urine test as baseline screening 2

Context-Specific Laboratory Testing

For Suspected Endocrine Causes

When chronic hypotension is present with specific clinical features, consider:

• Aldosterone-renin ratio for suspected adrenal insufficiency 2
• Plasma free metanephrines if pheochromocytoma suspected 2
• Late-night salivary cortisol or other cortisol screening tests 2
• Thyroid-stimulating hormone to exclude thyroid disease 2
• Serum electrolytes specifically looking for hyponatremia and hyperkalemia suggesting hypoaldosteronism 3

For Trauma or Hemorrhage

• Peripheral blood smear for assessment of schistocytes if thrombotic microangiopathy suspected 2
• Serial hematocrit measurements (though initial hematocrit has low sensitivity for detecting traumatic hemorrhage requiring surgical intervention) 1

Critical Monitoring Parameters

Continuous Assessment

• Fluid intake and output monitoring 1
• Daily weights 1
• Central venous oxygen saturation (SvO2) as marker of treatment response 1
• Serial lactate measurements to track resuscitation adequacy 1

Common Pitfalls to Avoid

• Do not rely on single hematocrit measurements as an isolated marker for bleeding in trauma 1
• Measure blood pressure in both arms to identify pressure differences from aortic dissection 2
• Obtain orthostatic vital signs (≥20 mmHg systolic or ≥10 mmHg diastolic drop defines orthostatic hypotension) 1
• Perform fundoscopy if malignant hypertension with rebound hypotension is suspected 2

Imaging When Indicated

• Chest X-ray or point-of-care ultrasound to discriminate cardiac from non-cardiac causes 2
• FAST exam (bedside ultrasound) in trauma or suspected intra-abdominal bleeding 1
• CT or MRI brain if intracranial hemorrhage or stroke suspected 2
• CT-angiography thorax/abdomen for acute aortic disease 2

The diagnostic approach should prioritize identifying life-threatening causes (cardiogenic shock, hemorrhage, sepsis, adrenal crisis) while simultaneously assessing end-organ perfusion through lactate and arterial blood gas analysis 1. Hemodynamically unstable patients require immediate intervention before completing the full diagnostic workup 1.