What initial labs should be checked in cases of episodes of hypotension?

Initial Laboratory Evaluation for Episodes of Hypotension

In cases of hypotension, initial laboratory evaluation should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, glucose, fasting lipid profile, liver function tests, and thyroid-stimulating hormone. 1

Essential Initial Laboratory Tests

Baseline Blood Tests

• Complete blood count (CBC): To assess for anemia, infection, or other hematologic abnormalities
• Serum electrolytes: Including sodium, potassium, calcium, and magnesium to identify electrolyte imbalances that may cause or worsen hypotension
• Renal function tests: Blood urea nitrogen (BUN) and serum creatinine to evaluate kidney function and volume status
• Blood glucose: To rule out hypoglycemia as a cause of hypotension
• Liver function tests: To assess hepatic function and potential causes of hypotension
• Thyroid-stimulating hormone (TSH): To screen for thyroid dysfunction

Additional Initial Tests

• Urinalysis: To evaluate for infection or renal disease
• Fasting lipid profile: To assess cardiovascular risk factors
• Electrocardiogram (ECG): Should be performed on all patients with hypotension 1

Specialized Testing Based on Clinical Suspicion

For Suspected Cardiac Causes

• Cardiac biomarkers: Troponin to rule out myocardial ischemia 1
• Echocardiography: For patients with suspected cardiac dysfunction 1

For Suspected Endocrine Causes

• Screening for hemochromatosis: Fasting transferrin saturation in selected patients 1
• HIV testing: Reasonable in high-risk patients 1
• Adrenal function tests: For suspected adrenal insufficiency 2

For Suspected Orthostatic Hypotension

• Orthostatic vital signs: Measure blood pressure after 5 minutes of rest in supine position, followed by measurements at 1 and 3 minutes after standing 3
• Heart rate response to standing: To assess baroreflex function and differentiate neurogenic from non-neurogenic causes 4

For Trauma Patients

• Coagulation studies: Prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), and fibrinogen 1
• Arterial blood gases: To assess oxygenation and acid-base status in severe cases 1
• Lactate levels: To evaluate tissue perfusion 1

Age-Specific Considerations

• Elderly patients (≥65 years): Consider a higher threshold for defining hypotension (SBP <117 mmHg) when interpreting laboratory results 5
• Middle-aged adults (36-64 years): Consider SBP <96 mmHg as hypotension 5
• Young adults (18-35 years): Traditional definition of hypotension (SBP <90 mmHg or <85 mmHg) remains appropriate 5

Monitoring Recommendations

• Serial monitoring of serum electrolytes and renal function is essential in patients with ongoing hypotension 1
• Capillary blood glucose should be checked immediately in patients with hypotension, especially when altered mental status is present 1
• Volume status assessment should be performed at each patient encounter through serial weight measurements, jugular venous pressure estimation, and evaluation for peripheral edema 1

Common Pitfalls to Avoid

• Do not rely on single hematocrit measurements as an isolated marker for bleeding, as they have low sensitivity (0.5) for detecting hemorrhage requiring intervention 1
• Do not delay treatment while waiting for laboratory results in severely hypotensive patients
• Do not overlook medication effects as potential causes of chronic hypotension 6
• Do not assume normotension is reassuring in elderly patients, as they may be relatively hypotensive even with "normal" blood pressure readings 5

Following this systematic approach to laboratory evaluation will help identify the underlying cause of hypotension and guide appropriate management strategies.