What is the cause of secondary hypertension in an asymptomatic 18-year-old patient with elevated blood pressure?

Secondary Hypertension in an 18-Year-Old

In an 18-year-old with blood pressure of 164/90 and no symptoms, the most likely causes of secondary hypertension are renal parenchymal disease and coarctation of the aorta, with renovascular disease (particularly fibromuscular dysplasia) also being an important consideration in this age group. 1, 2, 3

Why Secondary Hypertension Should Be Suspected

This patient meets multiple criteria that mandate evaluation for secondary causes:

• Age of onset before 30 years is a key red flag, particularly when hypertension occurs before age 20 1, 2, 4, 5
• Substantial blood pressure elevation (164/90 mmHg exceeds the 95th percentile for an 18-year-old male, which is approximately 132-140/85 mmHg) 1
• The European Society of Cardiology specifically recommends comprehensive screening for secondary hypertension in adults diagnosed before age 40 years 4

Most Likely Causes in This Age Group

Renal Parenchymal Disease

• Most common secondary cause in young patients, accounting for the majority of cases in children and adolescents 1, 3, 6
• Look for history of urinary tract infections, obstruction, hematuria, urinary frequency, nocturia, analgesic abuse, or family history of polycystic kidney disease 2, 7
• Initial screening includes serum creatinine, eGFR, and urinalysis with urinary albumin-to-creatinine ratio 2

Coarctation of the Aorta

• Critical diagnosis in young patients that requires immediate identification 1, 3
• Measure blood pressure in both arms and thighs—lower BP in legs compared to arms is diagnostic 2, 4
• Check for radio-femoral pulse delay and diminished or absent femoral pulses 2, 5
• Confirm with echocardiography or CT/MR angiography of the thoracic and abdominal aorta 2, 7

Renovascular Disease (Fibromuscular Dysplasia)

• Fibromuscular dysplasia is the most common renovascular cause in young adults, particularly women under 40 years 1, 7, 6
• Consider if there is abrupt onset of hypertension, flash pulmonary edema, or resistant hypertension 1, 2
• Screen with renal ultrasound with Duplex Doppler, followed by CT or MR renal angiography if positive 2, 7

Essential Initial Workup

History and Physical Examination

• Cardiovascular examination: Check for radio-femoral delay, diminished femoral pulses, and abdominal bruits 2, 5
• Medication review: NSAIDs, stimulants, decongestants, herbal supplements (especially ephedra), and recreational drugs can cause hypertension 1, 7
• Renal history: Previous UTIs, hematuria, family history of kidney disease 2, 7
• Sleep symptoms: Snoring, daytime sleepiness, witnessed apneas (though less common in thin 18-year-olds) 2, 7

Basic Laboratory Screening

• Serum creatinine and eGFR 2, 7
• Urinalysis and urinary albumin-to-creatinine ratio 2, 7
• Serum sodium and potassium (unprovoked hypokalemia suggests primary aldosteronism) 2, 7
• Fasting blood glucose or HbA1c 2
• Thyroid-stimulating hormone 2, 7
• 12-lead ECG 2

Targeted Testing Based on Initial Findings

• If abnormal renal function or urinalysis: Renal ultrasound to assess kidney size and structure 2, 7
• If BP differential between arms/legs or pulse abnormalities: Echocardiography and CT/MR angiography for coarctation 2, 7
• If hypokalemia or resistant hypertension: Plasma aldosterone-to-renin ratio for primary aldosteronism 1, 2, 7

Less Common but Important Causes in Young Adults

Primary Aldosteronism

• Affects 8-20% of resistant hypertension cases but can occur at any age 1, 7
• Screen if spontaneous or diuretic-induced hypokalemia, muscle cramps/weakness, or family history of early-onset hypertension 2, 7

Obstructive Sleep Apnea

• Less likely in an asymptomatic 18-year-old unless obese 2, 7
• Consider if BMI elevated, snoring, or daytime sleepiness present 2, 7

Drug-Induced Hypertension

• Always review before pursuing expensive workup 7
• Common culprits: NSAIDs, oral contraceptives, stimulants (prescription or recreational), decongestants, anabolic steroids 1

Critical Pitfalls to Avoid

• Do not assume primary hypertension based on obesity alone—even obese young patients with hypertension warrant screening for secondary causes, particularly sleep apnea 1, 2
• Do not delay evaluation of coarctation—this is a surgical emergency if severe and can be easily missed without checking leg blood pressures 2, 4
• Do not perform expensive imaging before completing basic laboratory screening and medication review 2
• Up to 85% of children and adolescents with hypertension have an identifiable secondary cause, making thorough evaluation essential in this age group 6

Management Approach

• Treat the underlying cause when identified—this can lead to cure or dramatic improvement in blood pressure control 2, 7
• Refer to specialized centers for complex cases requiring advanced diagnostic evaluation or surgical intervention 2, 8
• Even after treating the underlying cause, some patients may require ongoing antihypertensive therapy if vascular remodeling has occurred 2