What is the appropriate workup for an 18-year-old presenting with fatigue, weight gain, and lightheadedness?

Comprehensive Workup for an 18-Year-Old with Fatigue, Weight Gain, and Lightheadedness

A comprehensive laboratory assessment including thyroid function tests, metabolic panel, complete blood count, and screening for anemia should be the initial workup for an 18-year-old presenting with fatigue, weight gain, and lightheadedness.

Initial Assessment

Key History Elements

• Duration and pattern of weight gain
• Energy level changes and fatigue patterns
• Lightheadedness triggers (positional, exertional, or random)
• Menstrual history (if female)
• Sleep patterns and quality
• Dietary habits and recent changes
• Physical activity levels
• Family history of thyroid disorders, diabetes, or obesity
• Medication use (including contraceptives)
• Stress levels and mental health symptoms

Physical Examination Focus

• BMI calculation and plotting on age-appropriate charts
• Blood pressure measurement (three separate readings)
• Examination for signs of thyroid dysfunction:
  • Thyromegaly
  • Skin changes (dryness, texture)
  • Hair loss
  • Delayed relaxation of deep tendon reflexes
• Assessment for acanthosis nigricans (associated with insulin resistance)
• Evaluation for cushingoid features (striae, central obesity, moon facies)

Laboratory Workup

First-Line Testing

1. Thyroid Function Tests

   • TSH (primary screening test) 1
   • Free T4 if TSH is abnormal

2. Metabolic Assessment

   • Fasting glucose 2
   • Hemoglobin A1c
   • Fasting lipid panel (total cholesterol, LDL, HDL, triglycerides) 2
   • Fasting insulin (to assess insulin resistance)

3. Complete Blood Count

   • To evaluate for anemia or other hematologic abnormalities

4. Additional Basic Tests

   • Comprehensive metabolic panel (liver and kidney function)
   • Serum electrolytes (including calcium, magnesium)
   • Ferritin levels

Second-Line Testing (Based on Initial Results)

• Morning cortisol if cushingoid features present
• Vitamin D levels
• Inflammatory markers (high-sensitivity CRP)
• Sleep study if symptoms of obstructive sleep apnea are present 2

Specific Considerations

Thyroid Evaluation

Thyroid dysfunction is a common cause of fatigue and weight gain in adolescents. The USPSTF notes that TSH has high sensitivity (98%) and specificity (92%) when used to confirm suspected thyroid disease 1. Subclinical hypothyroidism can cause fatigue and weight gain even with mild TSH elevations.

Metabolic Assessment

According to the American Academy of Pediatrics guidelines, adolescents with weight gain should undergo comprehensive metabolic assessment, as obesity significantly increases the risk of cardiometabolic complications 2. Abnormal values to watch for include:

• Fasting glucose ≥100 mg/dL
• Total cholesterol >170 mg/dL
• LDL >110 mg/dL
• HDL <45 mg/dL
• Triglycerides >100 mg/dL

Cardiovascular Evaluation

The lightheadedness reported may have cardiovascular origins. Blood pressure should be measured carefully, with abnormal values defined as >95th percentile for age, height, and sex 2. Consider orthostatic vital signs if lightheadedness is positional.

Mental Health Screening

Psychological factors can contribute to both fatigue and weight gain. Screening for depression, anxiety, and eating disorders is recommended 2. The American Heart Association notes that psychological disorders may manifest with physical symptoms and can impact weight management.

Management Algorithm

1. If thyroid dysfunction is detected:

   • Initiate levothyroxine for hypothyroidism with careful monitoring for cardiac effects 3
   • Monitor for potential side effects including increased appetite, which could exacerbate weight gain

2. If metabolic abnormalities are found:

   • Implement lifestyle modifications focusing on diet and physical activity
   • Consider referral to a multidisciplinary program for comprehensive management 1
   • Monitor for progression to diabetes or cardiovascular disease

3. If anemia or nutritional deficiencies are identified:

   • Address specific deficiencies with appropriate supplementation
   • Evaluate for underlying causes of malabsorption

4. If normal initial laboratory findings:

   • Consider sleep study to evaluate for sleep disorders
   • Assess for psychological factors including anxiety, depression
   • Evaluate for deconditioning and low physical activity levels 4

Important Considerations

• Low levels of physical activity are associated with dysregulation of energy intake and fat mass gain 4, which may explain the constellation of symptoms
• Weight gain itself, even within the "normal" range, increases risk of medical illnesses 5
• Early intervention is critical as persistent weight gain creates a maintenance energy gap that becomes increasingly difficult to address 6
• Mental health screening should not be overlooked as psychological factors can manifest with physical symptoms 2

Follow-Up Recommendations

• Repeat laboratory assessment in 3 months if abnormalities are found
• If initial tests are normal but symptoms persist, consider expanded testing including endocrine evaluation
• Regular monitoring of BMI, blood pressure, and laboratory values is essential, with reassessment of cardiovascular risk factors if initial tests are normal but weight gain persists 2