What laboratory tests should be ordered for a patient with hypertension (high blood pressure) to assess underlying causes and cardiovascular risk?

Laboratory Tests for Hypertension

For any patient with hypertension, order the following essential laboratory tests: serum electrolytes (sodium, potassium), serum creatinine with estimated glomerular filtration rate (eGFR), fasting glucose, lipid profile, urinalysis with urinary albumin-to-creatinine ratio, and a 12-lead ECG. 1, 2

Core Laboratory Panel

Blood Tests

• Serum electrolytes (sodium, potassium, calcium, magnesium) to detect abnormalities suggesting secondary causes like primary aldosteronism (hypokalemia) or kidney dysfunction (hyperkalemia) 1, 2
• Serum creatinine with eGFR to assess kidney function and detect chronic kidney disease, which influences treatment decisions and cardiovascular risk 1, 2
• Fasting blood glucose and/or HbA1c to identify diabetes, which significantly increases cardiovascular risk and lowers treatment thresholds 2, 3
• Lipid profile (total cholesterol, LDL, HDL, triglycerides) for cardiovascular risk stratification and to guide statin therapy decisions 1, 2
• Complete blood count to detect anemia or other hematologic abnormalities 2, 4
• Thyroid-stimulating hormone (TSH) to screen for hypothyroidism and hyperthyroidism, both remediable causes of hypertension 2, 4
• Liver function tests as part of the comprehensive metabolic assessment 2

Urine Tests

• Urinalysis (dipstick) to screen for kidney disease 1, 2
• Urinary albumin-to-creatinine ratio rather than dipstick alone, as it is more sensitive for detecting early kidney damage and serves as an independent cardiovascular risk factor 2, 3, 4

Cardiac Assessment

• 12-lead ECG to detect atrial fibrillation, left ventricular hypertrophy, and ischemic heart disease 1, 2, 3

Rationale for Each Test

The laboratory workup serves three critical purposes: identifying target organ damage (particularly kidney dysfunction through creatinine, eGFR, and urinary albumin), screening for secondary causes of hypertension (through electrolytes, TSH, and kidney function), and assessing cardiovascular risk (through lipid profile and glucose measurements) 2. Baseline values are essential before initiating medications like diuretics or RAS blockers to monitor for medication side effects 2.

Elevated creatinine or reduced eGFR indicates kidney damage and is a very potent independent risk factor for mortality, with 8-year mortality more than three times higher in persons with serum creatinine ≥1.7 mg/dl 5. Proteinuria or albuminuria indicates kidney damage and serves as an independent cardiovascular risk factor 3. More than 50% of hypertensive patients have additional cardiovascular risk factors (diabetes 15-20%, lipid disorders 30%, obesity 40%, hyperuricemia 25%), which proportionally increase the risk of coronary, cerebrovascular, and renal diseases 1, 3.

Additional Tests When Clinically Indicated

For Suspected Secondary Hypertension

Order targeted testing when clinical features suggest specific causes 3:

• Aldosterone-renin ratio for suspected primary aldosteronism (especially with hypokalemia, resistant hypertension, or age <30 years) 1
• Plasma free metanephrines for suspected pheochromocytoma 1
• Late-night salivary cortisol or other screening tests for cortisol excess in suspected Cushing syndrome 1
• Serum uric acid levels, as elevated uric acid is common in hypertension and should be treated in symptomatic patients 1, 4

Imaging Studies

• Echocardiography when ECG shows abnormalities, cardiac murmurs are detected, cardiac symptoms are present, or detection of left ventricular hypertrophy would influence treatment decisions 2, 3
• Fundoscopy in severe or uncontrolled hypertension to assess for retinal changes, hemorrhages, or papilledema 2, 3
• Renal ultrasound for suspected kidney disease, chronic kidney disease assessment, or resistant hypertension 3
• Carotid ultrasound to detect atherosclerotic plaques or stenosis in patients with documented vascular disease elsewhere 1, 3

Critical Pitfalls to Avoid

Do not use urine dipstick alone for albuminuria screening—always order urinary albumin-to-creatinine ratio, as it is more sensitive for detecting early kidney damage 4. Do not skip the ECG even in young patients, as it is essential for detecting left ventricular hypertrophy and arrhythmias 4. Ignoring baseline values before starting medications makes it difficult to monitor for medication side effects 2. Do not overlook secondary causes in young patients (<30 years), patients with resistant hypertension, or those with abrupt onset rather than gradual increase, as the prevalence of secondary hypertension is higher in these populations 4, 6.

Special Considerations for Young Adults

In adults ≤30 years with elevated blood pressure, measure thigh blood pressure; if lower than arm pressures, consider coarctation of the aorta 4. Young patients with hypertension warrant heightened suspicion for secondary causes, particularly given the absence of typical risk factors like obesity, family history, or gradual onset 4.