What labs should be ordered for a patient presenting with fatigue?

Laboratory Workup for Fatigue

The initial laboratory workup for a patient presenting with fatigue should include complete blood count, comprehensive metabolic panel, thyroid-stimulating hormone, urinalysis, and inflammatory markers (ESR, CRP) if indicated by clinical presentation. 1

Initial Assessment

Before ordering laboratory tests, quantify fatigue severity using a 0-10 scale:

• 0 = no fatigue
• 1-3 = mild fatigue (requires education only)
• 4-6 = moderate fatigue (requires evaluation)
• 7-10 = severe fatigue (requires prompt evaluation) 1

Laboratory Testing Algorithm

First-Line Laboratory Tests (for moderate to severe fatigue)

• Complete blood count with differential 2, 1
• Comprehensive metabolic panel (including electrolytes, renal and liver function) 2, 1
• Thyroid-stimulating hormone (TSH) 2, 1
• Urinalysis 2
• Fasting blood glucose or glycohemoglobin 2

Additional Tests Based on Clinical Suspicion

• Inflammatory markers (ESR, CRP) if inflammatory condition suspected 1
• Lipid profile 2
• Serum calcium and magnesium 2

Diagnostic Imaging and Other Tests

• Chest radiograph (PA and lateral) if respiratory symptoms present 2
• 12-lead electrocardiogram if cardiac symptoms present 2
• Consider echocardiography if cardiac dysfunction suspected 2

Special Considerations

Cancer Survivors

For cancer survivors with fatigue, compare current hemoglobin/hematocrit with end-of-treatment values and assess other cell lines (WBC and platelets) 2

Chronic Fatigue

For patients with persistent fatigue without clear cause after initial workup:

• Avoid excessive testing, as only about 5% of chronic fatigue cases are due to organic causes 1
• Previously undiagnosed cancer accounts for only 0.6% of fatigue cases 1

Common Pitfalls to Avoid

1. Over-testing: Extensive laboratory evaluation rarely yields significant diagnoses in the absence of other symptoms or abnormal physical findings 3

2. Under-evaluation: Failing to screen for common treatable causes like anemia, hypothyroidism, and depression 1

3. Ignoring medication side effects: Many medications can cause fatigue, including pain medications, sleep aids, and antiemetics 2

4. Missing ME/CFS: Post-exertional malaise is the hallmark symptom of myalgic encephalomyelitis/chronic fatigue syndrome and requires specific management approaches 4

5. Overlooking psychological factors: Depression and anxiety are common causes of fatigue and should be assessed alongside physical causes 5, 6

Remember that laboratory testing should be directed by history and physical examination findings rather than ordered as a standard battery for all patients with fatigue 1, 3.