Laboratory Workup for Fatigue
For patients with moderate to severe fatigue (score ≥4 on a 0-10 scale), the recommended laboratory evaluation includes: complete blood count with differential, comprehensive metabolic panel, and thyroid-stimulating hormone (TSH). 1, 2
Initial Screening Determines Lab Necessity
- Screen all patients using a 0-10 numeric rating scale where 0-3 indicates mild fatigue, 4-6 moderate, and 7-10 severe 1, 3
- Only patients scoring ≥4 warrant laboratory testing—those with mild fatigue (0-3) require no lab work, just rescreening at intervals 1, 3
- Laboratory evaluation should be guided by the presence of other symptoms, onset timing, and severity of fatigue 1
Core Laboratory Panel
Essential Tests for All Moderate-to-Severe Cases
Complete Blood Count (CBC) with Differential 1, 2
- Compare current hemoglobin/hematocrit with baseline or end-of-treatment values to detect anemia 1
- Assess white blood cell count and platelets to screen for infection or hematologic malignancy 1
Comprehensive Metabolic Panel (CMP) 1, 2
- Evaluate electrolyte abnormalities that may cause fatigue 1
- Assess hepatic function to detect liver disease 1
- Assess renal function to identify kidney dysfunction 1
Thyroid-Stimulating Hormone (TSH) 1, 2
- Screen for hypothyroidism, a common treatable cause of fatigue 1
- Consider more comprehensive endocrinologic evaluation or specialist referral if other endocrine symptoms are present 1
- Particularly important for patients who received radiation to the neck or thorax 1
Additional Testing Based on Clinical Context
Inflammatory Markers 2
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) when inflammatory conditions are suspected 2
Infectious Disease Screening 2
- HIV testing and tuberculosis screening if risk factors are present 2
Cardiac Evaluation 1
- Echocardiogram for patients who received cardiotoxic treatments (e.g., anthracyclines, trastuzumab) 1
Critical Context: When Labs Are Most Valuable
The evidence consistently shows that laboratory studies affect management in only 5% of patients with fatigue 4. This underscores the importance of:
- Targeting lab work to patients with moderate-to-severe symptoms (≥4/10) rather than universal testing 1
- Avoiding repeat testing if initial results are normal unless clinical status changes 4
- Recognizing that the predictive value of laboratory tests is low in fatigue workups 1
What Labs DON'T Replace
Laboratory testing must be paired with assessment of treatable contributing factors that often explain fatigue better than lab abnormalities 1:
- Pain assessment and management (pain commonly clusters with fatigue) 1, 3
- Emotional distress screening for depression and anxiety using validated tools 1, 3
- Sleep disturbance evaluation including quality, quantity, and sleep hygiene 1, 3
- Medication review for sedating effects, including over-the-counter drugs and supplements 1, 2
- Nutritional assessment including weight changes and caloric intake 1, 2
- Activity level and deconditioning evaluation 1, 2
Common Pitfalls to Avoid
- Don't order extensive lab panels for mild fatigue (scores 0-3)—this leads to unnecessary testing and false positives 1, 3
- Don't repeat normal labs without clinical indication—if initial workup is negative, repeat testing rarely yields new information 4
- Don't rely solely on labs to explain fatigue—the history, physical exam, and assessment of contributing factors are more clinically valuable 1
- Don't overlook medication side effects—review all prescriptions, over-the-counter medications, and supplements as potential contributors 1, 3
Special Population Considerations
Cancer Survivors 1
- Timing of fatigue onset relative to treatment completion guides workup intensity 1
- Mild-to-moderate fatigue persisting 6-12 months post-treatment may not warrant extensive workup unless other symptoms present 1
- New or worsening moderate-to-severe fatigue after this period requires more extensive evaluation to screen for metastatic disease 1
Elderly Patients 2