What are the causes of hypertension in infants and how should it be evaluated?

Causes and Evaluation of Hypertension in Infants

In infants, hypertension is most commonly caused by umbilical catheter-associated thrombosis, renal parenchymal disease, and chronic lung disease, and should be evaluated systematically with renal ultrasonography, basic metabolic panel, and urinalysis as the initial workup. 1, 2

Primary Causes in Infants

The etiology of hypertension in infants differs substantially from older children, with secondary causes predominating:

Most Common Causes (in order of frequency):

• Umbilical catheter-associated thrombosis (aortic or renal artery)
• Renal parenchymal disease (congenital anomalies, dysplasia, polycystic kidney disease)
• Chronic lung disease (bronchopulmonary dysplasia in premature infants)
• Coarctation of the aorta (presents with upper extremity BP ≥20 mmHg higher than lower extremity)
• Renovascular disease (renal artery stenosis, thromboembolism)

1, 2, 3

Given that 50-80% of pediatric secondary hypertension stems from renal parenchymal and renovascular diseases, the initial evaluation must focus heavily on renal assessment 4.

Systematic Evaluation Approach

Step 1: Initial History and Physical Examination

Critical historical elements to obtain:

• Neonatal history: Umbilical catheter placement, duration, complications
• Gestational age and birth weight (major determinants of neonatal BP)
• Maternal factors during pregnancy
• Symptoms: Feeding difficulties, failure to thrive, respiratory distress, seizures, congestive heart failure
• Medications/drugs that may elevate BP

Essential physical examination findings:

• Four-limb blood pressures (upper and lower extremities to detect coarctation)
• Height, weight, body mass index
• Cardiovascular examination (murmurs, femoral pulses, perfusion)
• Abdominal examination (masses, bruits)
• Neurologic assessment

5, 6, 2

Step 2: Mandatory Initial Laboratory Tests

All hypertensive infants require:

1. Blood chemistry panel: sodium, potassium, chloride, total CO₂, creatinine (Grade D)
2. Urinalysis (Grade D)
3. Renal ultrasonography (Grade D)

4

Rationale: These three tests identify the vast majority of secondary causes in infants. Elevated creatinine, abnormal potassium, and renal abnormalities on ultrasound are highly associated with secondary hypertension 4.

Step 3: Additional Imaging Based on Initial Results

Doppler ultrasonography should follow if:

• Gray-scale ultrasound shows structural abnormalities
• Clinical suspicion for renovascular disease (history of umbilical catheterization)
• Detects renal arterial or aortic thrombosis
• Identifies alterations in arterial waveform from renal artery narrowing

3

Important caveat: Doppler may miss disease in accessory renal arteries or small segmental intrarenal arteries 3.

Step 4: Assessment of Target Organ Damage

Routine evaluation for all confirmed hypertensive infants:

1. Echocardiography (Grade D) - assess for:

   • Left ventricular mass index
   • Systolic and diastolic LV function
   • Aortic arch evaluation (coarctation)

2. Retinal examination (Grade C) - up to 50% show abnormalities or arteriolar narrowing

3. Albumin-to-creatinine ratio (first morning specimen) (Grade D)

4, 6, 4

Blood Pressure Measurement Technique

Critical for accurate diagnosis:

• Use appropriate cuff size (bladder width = 40% of arm circumference)
• Auscultatory method preferred for diagnosis
• Oscillometric values must be confirmed with auscultation
• Compare to normative data for gestational age, birth weight, and postmenstrual age

4, 2

Staging and Urgency of Evaluation

Stage 1 hypertension (BP between 95th-99th percentile + 5 mmHg):

• Repeat measurements on 2 more occasions within 1 month
• If confirmed, initiate evaluation or referral within 1 month

Stage 2 hypertension (BP > 99th percentile + 5 mmHg):

• Prompt referral for immediate evaluation and therapy

4

Key Clinical Pitfalls to Avoid

1. Don't assume primary hypertension in infants - unlike older children and adolescents, infants almost always have secondary causes requiring identification 1, 2

2. Don't skip four-limb blood pressures - coarctation must be ruled out and presents with characteristic BP differential 5, 7

3. Don't delay renal imaging - renal ultrasonography is mandatory, not optional, given the predominance of renal causes 4

4. Don't overlook umbilical catheter history - this is the single most common iatrogenic cause in neonates and requires specific evaluation for thrombosis 1, 2

5. Don't use home BP monitoring for diagnosis - insufficient evidence in this age group; office measurements with proper technique are required 5, 8

When to Refer Immediately

• Stage 2 hypertension at presentation
• Symptomatic hypertension (seizures, heart failure, encephalopathy)
• Evidence of target organ damage on initial evaluation
• Suspected renovascular disease requiring specialized imaging or intervention

4

The evaluation must be expedited in infants given the high likelihood of treatable secondary causes and the potential for long-term cardiovascular consequences if left unaddressed 1, 2.