What are the initial lab tests for a patient with severe hypertension?

Initial Laboratory Workup for Severe Hypertension

For patients with severe hypertension, the initial laboratory workup should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, fasting blood glucose (glycohemoglobin), lipid profile, liver function tests, and thyroid-stimulating hormone. 1

Essential Laboratory Tests

• Blood tests:

  • Complete blood count 1
  • Serum electrolytes (sodium, potassium, calcium, magnesium) 1
  • Blood urea nitrogen and serum creatinine with estimated glomerular filtration rate (eGFR) 1
  • Fasting blood glucose and/or glycated hemoglobin (HbA1c) 1
  • Lipid profile (total cholesterol, LDL, HDL, triglycerides) 1
  • Liver function tests 1
  • Thyroid-stimulating hormone (TSH) 1
  • Serum uric acid (optional but recommended) 1

• Urine tests:

  • Urinalysis 1
  • Urinary albumin-to-creatinine ratio 1

• Cardiac assessment:

  • 12-lead electrocardiogram 1

Rationale for Testing

These laboratory tests serve multiple critical purposes in severe hypertension:

• Identify target organ damage: Kidney function tests (creatinine, eGFR, urinary albumin) help detect hypertension-mediated organ damage 1
• Screen for secondary causes: Electrolytes, TSH, and kidney function can identify conditions like primary aldosteronism, thyroid disorders, and renal disease 1
• Assess cardiovascular risk: Lipid profile and glucose measurements help stratify overall cardiovascular risk 1
• Guide treatment decisions: Baseline values of electrolytes and kidney function are essential before initiating medications like diuretics or RAS blockers 1

Additional Tests to Consider Based on Clinical Presentation

• Echocardiography: Recommended when ECG is abnormal, cardiac murmurs are detected, or cardiac symptoms are present 1
• Fundoscopy: Essential in severe hypertension (BP >180/110 mmHg) to assess for hypertensive retinopathy, hemorrhages, or papilledema 1
• Additional imaging: Consider renal ultrasound if kidney disease is suspected or in resistant hypertension 1

Clinical Implications of Laboratory Findings

• Abnormal electrolytes: Hypokalemia may suggest primary aldosteronism, while hyperkalemia may indicate kidney dysfunction or medication effects 1
• Elevated creatinine/reduced eGFR: Indicates kidney damage and influences treatment decisions 1
• Elevated glucose/HbA1c: Identifies comorbid diabetes, which significantly increases cardiovascular risk 1, 2
• Abnormal lipids: Guides decisions about statin therapy in addition to BP management 1, 3
• Proteinuria/albuminuria: Indicates kidney damage and is an independent cardiovascular risk factor 1

Common Pitfalls to Avoid

• Inadequate testing: Incomplete workup may miss comorbidities like diabetes, dyslipidemia, or chronic kidney disease that affect treatment decisions 2
• Over-testing: Extensive testing for secondary causes in all patients is unnecessary and costly unless clinical suspicion exists 4
• Ignoring baseline values: Failure to obtain baseline laboratory values before starting medications can make it difficult to monitor for medication side effects 1
• Delayed follow-up: Laboratory abnormalities should prompt appropriate follow-up testing and referrals 2

Recent evidence shows that patients receiving complete laboratory workup at diagnosis achieve better blood pressure control at 12 months compared to those with partial workup (129.9 ± 13.6 mmHg vs. 142.8 ± 18.9 mmHg) 2, highlighting the importance of comprehensive initial assessment in hypertension management.