What laboratory tests should be ordered for a walk‑in patient with severe hypertension (200/115 mm Hg) presenting with headaches?

Laboratory Testing for Severe Hypertension with Headache

For a walk-in patient with severe hypertension (200/115 mm Hg) and headaches, order a comprehensive metabolic panel (sodium, potassium, creatinine with eGFR, glucose, calcium), complete blood count, urinalysis, and ECG immediately to assess for hypertensive emergency and screen for secondary causes. 1

Immediate Assessment Priority

This blood pressure qualifies as a hypertensive crisis (systolic >180 mm Hg or diastolic >120 mm Hg) and requires urgent evaluation to distinguish between hypertensive urgency versus emergency. 2 The presence of headache raises concern for potential end-organ damage (hypertensive encephalopathy, intracranial hemorrhage), making this a potential hypertensive emergency until proven otherwise. 2

Essential Basic Laboratory Tests

Core Metabolic Panel

• Serum sodium and potassium: Hypokalemia suggests primary aldosteronism or renovascular disease as secondary causes. 1
• Serum creatinine with estimated glomerular filtration rate (eGFR): Assesses for acute kidney injury or chronic kidney disease as both cause and consequence of severe hypertension. 1
• Fasting blood glucose: Screens for diabetes as a cardiovascular risk factor and potential contributor to resistant hypertension. 1
• Serum calcium: May be included in comprehensive metabolic panel. 1

Additional Basic Tests

• Complete blood count: Evaluates for anemia, thrombocytopenia (HELLP syndrome if applicable), or polycythemia. 1
• Urinalysis with dipstick: Screens for proteinuria, hematuria, and red blood cell casts indicating hypertensive nephropathy or glomerulonephritis. 1
• 12-lead ECG: Detects left ventricular hypertrophy, acute coronary syndrome, arrhythmias, or conduction abnormalities. 1

Optional Tests Based on Clinical Context

If Considering Secondary Hypertension

The following warrant additional testing in this severe presentation:

• Thyroid-stimulating hormone (TSH): Screens for hypo- or hyperthyroidism as reversible causes. 1
• Lipid profile: Completes cardiovascular risk stratification. 1
• Urinary albumin-to-creatinine ratio: More sensitive than dipstick for detecting early kidney damage. 1

Red Flags for Secondary Causes in This Patient

This patient's severe hypertension (200/115 mm Hg) itself is a red flag. 3, 4 Additional screening for secondary hypertension should be considered if:

• Age <30 years or sudden onset in previously normotensive patient 3, 5, 4
• Resistant hypertension (if already on ≥3 medications including a diuretic) 3, 5, 4
• Spontaneous or diuretic-induced hypokalemia on basic labs 3, 4
• Acute rise in creatinine >50% after starting ACE inhibitor/ARB 6

Algorithmic Approach to Laboratory Ordering

Step 1: Order immediately upon presentation:

• Comprehensive metabolic panel (includes sodium, potassium, creatinine, eGFR, glucose, calcium) 1
• Complete blood count 1
• Urinalysis 1
• ECG 1

Step 2: Add if results pending or patient stable enough for outpatient workup:

• TSH 1
• Lipid profile 1
• Urinary albumin-to-creatinine ratio 1

Step 3: If basic labs reveal hypokalemia, young age, or resistant hypertension:

• Plasma aldosterone-to-renin ratio (ARR) for primary aldosteronism screening 3, 4

Critical Pitfalls to Avoid

• Do not delay treatment while waiting for laboratory results if clinical signs of hypertensive emergency are present (altered mental status, chest pain, dyspnea, focal neurologic deficits). 2
• Do not assume essential hypertension without reviewing medication adherence and substance use (NSAIDs, decongestants, cocaine, amphetamines, oral contraceptives). 3, 4, 7
• Do not order extensive secondary hypertension workup before confirming medication adherence and excluding white-coat effect with home or ambulatory blood pressure monitoring. 3, 4
• Do not miss acute kidney injury: A rise in creatinine may indicate hypertensive nephrosclerosis, renovascular disease, or medication effect. 6

When to Consider Advanced Testing

If basic labs show hypokalemia (<3.5 mEq/L), proceed with aldosterone-to-renin ratio. 3, 4 If creatinine is elevated or urinalysis shows proteinuria/hematuria, consider renal ultrasound. 1 If patient is <30 years old or has abdominal bruit on exam, consider renovascular imaging. 3, 5

Evidence Strength

The 2017 ACC/AHA guidelines 1, 2020 ISH guidelines 1, and 2013 ESH/ESC guidelines 1 all consistently recommend this basic laboratory panel for initial hypertension evaluation, with the most recent 2024 ESC update now recommending aldosterone-to-renin ratio screening for all confirmed hypertension cases. 3, 4