What laboratory tests should be ordered for a patient presenting with chronic fatigue?

Laboratory Tests for Chronic Fatigue

For patients with chronic fatigue, laboratory evaluation should include complete blood count, urinalysis, serum electrolytes, blood urea nitrogen, serum creatinine, glucose, lipid profile, liver function tests, iron studies, and thyroid-stimulating hormone to identify treatable causes. 1

Initial Screening Assessment

Before ordering laboratory tests, assess fatigue severity using a standardized scale:

• 0-10 scale (0 = no fatigue, 10 = worst fatigue imaginable)
• Categorize as mild (1-3), moderate (4-6), or severe (7-10)
• Patients with moderate to severe fatigue (score ≥4) warrant comprehensive evaluation 1

Core Laboratory Panel

The following tests should be ordered for all patients with chronic fatigue:

1. Complete blood count (CBC) with differential

   • Identifies anemia, infection, or other hematologic abnormalities
   • Compare current hemoglobin/hematocrit with previous values if available 1

2. Comprehensive metabolic panel

   • Electrolytes (sodium, potassium, calcium, magnesium)
   • Renal function (BUN, creatinine)
   • Liver function tests (ALT, AST, alkaline phosphatase)
   • Glucose 1

3. Thyroid function tests

   • TSH is essential for all patients with fatigue
   • Consider more comprehensive evaluation if other thyroid symptoms present 1

4. Iron studies

   • Serum iron, ferritin, transferrin saturation
   • Particularly important to identify iron deficiency 1

5. Lipid profile

   • Total cholesterol, HDL, LDL, triglycerides 1

6. Urinalysis

   • Screens for renal disease, infection, or other abnormalities 1

Additional Testing Based on Clinical Context

Consider these additional tests when clinically indicated:

1. Inflammatory markers

   • ESR or CRP if inflammatory or autoimmune conditions suspected

2. B-type natriuretic peptide (BNP) or NT-proBNP

   • If heart failure is suspected as a cause of fatigue 1

3. Antinuclear antibodies (ANA)

   • If autoimmune disease is suspected 2

4. Specialized endocrine testing

   • Consider more comprehensive evaluation if specific endocrine disorders suspected 1

Clinical Pearls and Pitfalls

• Laboratory abnormalities alone may not explain fatigue; interpret results in clinical context 3
• Mild to moderate fatigue persisting 6-12 months after cancer treatment may not warrant extensive workup unless other symptoms are present 1
• Psychological assessment is important as depression and anxiety commonly coexist with chronic fatigue 3
• Serial monitoring of laboratory values may be necessary when following response to treatment
• Abnormal laboratory findings should prompt appropriate referral to specialists (e.g., cardiologist, endocrinologist, mental health professional) 1

When to Consider Expanded Testing

Expand laboratory evaluation when:

• Moderate to severe fatigue (score ≥7) significantly impacts quality of life
• Other symptoms are present (pain, pulmonary complaints, unintentional weight loss)
• Initial laboratory tests are normal but symptoms persist or worsen
• Red flag symptoms suggest specific organ system involvement

Remember that chronic fatigue often has multifactorial causes, and laboratory tests should be interpreted as part of a comprehensive clinical assessment that includes evaluation of sleep quality, pain, medication effects, and psychological factors.