What labs should be ordered for a teenager presenting with acanthosis (a skin condition characterized by dark, velvety skin patches)?

Laboratory Testing for Teenagers with Acanthosis Nigricans

For teenagers presenting with acanthosis nigricans, fasting plasma glucose, 2-hour glucose tolerance test, and A1C should be ordered as the primary screening tests, along with a fasting lipid panel and insulin levels to evaluate for insulin resistance and metabolic abnormalities. 1

Understanding Acanthosis Nigricans

Acanthosis nigricans is characterized by dark, velvety skin patches typically found in skin folds and is strongly associated with insulin resistance and metabolic disorders. In teenagers, it serves as an important clinical marker that warrants comprehensive metabolic evaluation.

Primary Laboratory Tests

Diabetes/Insulin Resistance Screening

• Fasting plasma glucose (FPG) - Primary screening test 1
• 2-hour plasma glucose during 75-g oral glucose tolerance test (OGTT) - Especially important when FPG is normal but diabetes is still suspected 1
• Hemoglobin A1C - For evaluation of long-term glycemic control 1
• Fasting insulin level - To assess for hyperinsulinemia and calculate HOMA-IR 1, 2

Lipid Panel

• Complete lipid profile including:
  • Total cholesterol
  • LDL cholesterol
  • HDL cholesterol
  • Triglycerides 1

Additional Testing Based on Clinical Presentation

For Suspected Polycystic Ovary Syndrome (PCOS)

For female adolescents with menstrual irregularities or other signs of PCOS:

• Total testosterone or bioavailable/free testosterone 1
• Sex hormone binding globulin 1

For Suspected Thyroid Dysfunction

• Thyroid-stimulating hormone (TSH) 1

For Suspected Liver Involvement

• Alanine aminotransferase (ALT) - To screen for metabolic dysfunction-associated steatotic liver disease 3

Testing Frequency and Follow-up

• If initial screening is normal, repeat testing at minimum 3-year intervals 1
• More frequent testing if BMI is increasing or risk factors worsen 1

Clinical Pearls and Pitfalls

• Important: Acanthosis nigricans is strongly associated with insulin resistance - 29% of youth with acanthosis nigricans have abnormal glucose homeostasis 2
• Caution: While obesity is the most common cause of acanthosis nigricans in teenagers, rarely it can be associated with malignancy, particularly in cases with sudden onset, rapid progression, or extensive distribution 4
• Remember: The presence of acanthosis nigricans alone predicts hyperinsulinemia and insulin resistance in approximately 7% of overweight adolescents 5
• Consider: In cases where type 2 diabetes is suspected, testing for pancreatic autoantibodies may be necessary to exclude autoimmune type 1 diabetes, as diabetes-associated autoantibodies can be present in patients with clinical features of type 2 diabetes 1

Risk Stratification

Testing is particularly important for teenagers with acanthosis nigricans who have additional risk factors:

• BMI ≥85th percentile (overweight) or ≥95th percentile (obesity)
• Family history of type 2 diabetes in first- or second-degree relatives
• High-risk race/ethnicity (African American, Latino, Native American, Asian American, Pacific Islander)
• Signs of other conditions associated with insulin resistance (hypertension, dyslipidemia, PCOS)
• Maternal history of diabetes or gestational diabetes during the child's gestation 1

By following this comprehensive laboratory evaluation approach, clinicians can effectively identify metabolic abnormalities in teenagers with acanthosis nigricans and initiate appropriate interventions to reduce long-term morbidity and mortality.