In a school‑age child with blood pressure above the 95th percentile, obesity, acanthosis nigricans, and a family history of type 2 diabetes mellitus and hypertension, what is the next step to establish the diagnosis?

Next Step in Diagnosis

In this obese school-age child with confirmed hypertension, acanthosis nigricans, and a family history of type 2 diabetes and hypertension, the next step is to obtain fasting plasma glucose, fasting insulin, lipid profile, basic metabolic panel, and urinalysis to screen for insulin resistance syndrome and metabolic complications—not to pursue extensive evaluation for rare secondary causes of hypertension. 1

Rationale for Metabolic Screening

This clinical presentation strongly suggests primary hypertension with insulin resistance syndrome, not secondary hypertension requiring specialized testing like aldosterone-renin ratio, catecholamines, or renal artery ultrasound. 1

Key Clinical Features Supporting This Approach:

• Acanthosis nigricans is a cutaneous marker of insulin resistance and specifically warrants screening for insulin resistance and type 2 diabetes in obese children 1
• The American Heart Association explicitly recommends fasting plasma glucose testing for children who are overweight and have signs of insulin resistance such as acanthosis nigricans and hypertension 1
• The 2017 AAP guidelines state that children ≥6 years who are overweight/obese with positive family history do not require extensive evaluation for secondary causes if there are no specific findings suggesting secondary hypertension 1

Recommended Initial Laboratory Panel

Essential Tests:

• Fasting plasma glucose - primary screening test for insulin resistance syndrome 1
• Fasting insulin and HOMA-IR calculation - provides better assessment of insulin resistance than glucose alone 1
• Lipid profile - dyslipidemia is part of insulin resistance syndrome 1
• Basic metabolic panel (electrolytes, creatinine) - screens for renal parenchymal disease 1
• Urinalysis - screens for renal involvement 1

Supporting Evidence:

Obese children with acanthosis nigricans demonstrate significantly higher fasting insulin (19.9 vs 10.4 mU/L), post-meal insulin (88.6 vs 51.1 mU/L), and HOMA-IR (4.0 vs 2.2) compared to obese children without acanthosis nigricans 2. This makes metabolic screening the logical first step rather than pursuing rare endocrine causes.

Why NOT the Listed Options

Option A (Aldosterone-Renin Ratio, Catecholamines):

• These tests evaluate for rare secondary causes (primary hyperaldosteronism, pheochromocytoma) 3
• Not indicated in obese children with acanthosis nigricans and family history of metabolic disease 1
• The clinical picture points to insulin resistance, not endocrine tumors 1

Option B (Renal Artery Ultrasound):

• Evaluates for renovascular disease and structural renal abnormalities 4
• Not first-line in children ≥6 years who are overweight/obese without specific findings suggesting secondary hypertension 1
• Would be considered if: stage 2 hypertension, significant diastolic elevation, or abnormal screening labs suggesting renal disease 4

Option C (Cortisol Level):

• Screens for Cushing's syndrome 3
• Not indicated without specific clinical features (striae, moon facies, buffalo hump, growth deceleration) 3
• Obesity alone does not warrant cortisol screening 3

Clinical Context

The American Academy of Pediatrics recommends ambulatory BP monitoring to confirm hypertension diagnosis before extensive laboratory workup 1. However, once hypertension is confirmed (as stated in this case with repeat measurements above 95th percentile), the American Heart Association recommends metabolic screening as the initial approach in obese children with acanthosis nigricans, rather than evaluation for rare secondary causes 1.

Important Caveat:

Children and adolescents with BMI >95th percentile should undergo blood pressure measurement, lipoprotein analysis, and fasting insulin and glucose determination 3. The presence of acanthosis nigricans makes this evaluation even more critical, as it indicates established insulin resistance 5, 6.

When to Consider Secondary Causes

Pursue evaluation for secondary hypertension (including renal artery ultrasound, endocrine testing) if: 3, 4

• Stage 2 hypertension (≥95th percentile + 12 mm Hg)
• History or physical findings suggesting specific secondary causes
• Abnormal screening laboratories (hypokalemia, elevated creatinine, abnormal urinalysis)
• Lack of response to lifestyle modifications and initial antihypertensive therapy
• Age <6 years (where secondary causes predominate)