What laboratory tests are recommended for patients presenting with fatigue?

Laboratory Tests for Patients Presenting with Fatigue

Initial laboratory evaluation for patients presenting with fatigue should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, fasting blood glucose (glycohemoglobin), lipid profile, liver function tests, and thyroid-stimulating hormone. 1

Core Laboratory Tests

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

• Complete blood count (CBC) to assess for anemia, infection, or hematologic disorders 1, 2
• Urinalysis to screen for renal disease or infection 1
• Serum electrolytes including calcium and magnesium to identify electrolyte imbalances 1
• Blood urea nitrogen (BUN) and serum creatinine to evaluate kidney function 1
• Fasting blood glucose or glycohemoglobin (HbA1c) to screen for diabetes 1
• Lipid profile to assess cardiovascular risk 1
• Liver function tests to evaluate hepatic disorders 1
• Thyroid-stimulating hormone (TSH) to screen for thyroid dysfunction 1

Additional Testing Based on Clinical Context

For patients with moderate to severe fatigue, consider additional targeted testing:

• For cancer patients or survivors: Consider evaluating disease status and performing a comprehensive assessment of contributing factors 1
• For patients with suspected heart failure: Consider B-type natriuretic peptide (BNP) or N-terminal pro-B-type natriuretic peptide (NT-proBNP) 1
• For patients with suspected inflammatory conditions: Consider erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) 3

Assessment Algorithm

1. Quantify fatigue severity using a 0-10 numeric rating scale:

   • Mild: 1-3
   • Moderate: 4-6
   • Severe: 7-10 1

2. Order core laboratory tests for all patients with fatigue 1

3. For moderate to severe fatigue (score ≥4), perform:

   • Focused fatigue history (onset, pattern, duration)
   • Thorough medical examination
   • Review of body systems
   • Mental status examination 1

4. Consider specialized testing based on clinical suspicion:

   • Screening for hemochromatosis or HIV in selected patients 1
   • Diagnostic tests for rheumatologic diseases, amyloidosis, or other specific conditions when clinically indicated 1
   • Electrocardiogram and chest radiograph if cardiovascular or pulmonary causes are suspected 1

Important Considerations

• Laboratory abnormalities alone may not explain fatigue - psychological factors often play a significant role in chronic fatigue 3, 4
• Fatigue assessment should be ongoing, as levels may change throughout disease course 5
• The predictive value of laboratory tests is relatively low in cancer-related fatigue, but they remain important to rule out treatable causes 1
• Fatigue often coexists with other symptoms, so a multisymptom screening approach may be valuable 1

Common Pitfalls to Avoid

• Failing to quantify fatigue severity using a standardized scale 1
• Overlooking psychological causes of fatigue, which are common 3, 4
• Attributing fatigue solely to laboratory abnormalities without considering the full clinical picture 3
• Not reassessing fatigue over time, as it may be persistent or change in character 5
• Neglecting to screen for comorbid conditions that may contribute to fatigue 1