Essential Laboratory Evaluation for Adult Fatigue
Core Laboratory Tests for All Patients
- Complete blood count (CBC) – recommended to detect anemia, infection, or hematologic disorders as part of the initial fatigue work‑up. 1
- Thyroid‑stimulating hormone (TSH) – screening for hypothyroidism or hyperthyroidism, which are common contributors to fatigue in women. 2
- Comprehensive metabolic panel – includes serum electrolytes, calcium, magnesium, blood urea nitrogen, and creatinine to assess electrolyte balance, bone mineral status, and kidney function. 1
- Fasting blood glucose or hemoglobin A1c – used to screen for diabetes mellitus, a treatable cause of chronic fatigue. 1
- Liver function tests (ALT, AST, total bilirubin, alkaline phosphatase, albumin) – evaluate for hepatic disease that may manifest with fatigue. 1
- Urinalysis – screens for renal pathology or urinary‑tract infection that can contribute to generalized tiredness. 1
- Fasting lipid profile – assesses cardiovascular risk factors that may underlie fatigue‑related reduced perfusion. 1
Additional Tests Guided by Clinical Context
- Erythrocyte sedimentation rate (ESR) – obtain when an inflammatory or rheumatologic condition is suspected. 3
- Iron studies (serum iron, ferritin, total iron‑binding capacity) – indicated for patients with anemia or suspected iron deficiency; low iron stores can cause fatigue even in the absence of overt anemia. 4
- 25‑OH vitamin D level – deficiency is linked to muscle fatigue and correlates with self‑reported fatigue severity. 4
- Morning free testosterone – consider in individuals with unexplained weight loss, decreased libido, or depressive symptoms. 5
- Pregnancy test – essential for women of reproductive age to rule out pregnancy‑related fatigue. 6
Infectious and Systemic Disease Screening
- HIV testing – recommended for patients with relevant risk factors (e.g., high‑risk sexual behavior, injection drug use). 5
- Hepatitis B and C screening – indicated when risk factors such as prior transfusion, injection drug use, or occupational exposure are present. 5
- Latent tuberculosis screening (tuberculin skin test or interferon‑γ release assay) – performed in individuals with epidemiologic risk for TB exposure. 5
Clinical History Elements Supporting Laboratory Decision‑Making
- Assessment of associated symptoms – weight changes, temperature intolerance, mood alterations, and sleep disturbances should be systematically queried to guide targeted testing. [2][4]
- Depression screening – psychosocial evaluation, including validated depression tools, is advised for patients with persistent fatigue. 6
Laboratory Tests for Patients Presenting with Fatigue
Core Laboratory Tests
- The American Heart Association recommends initial laboratory evaluation for patients presenting with fatigue should include complete blood count, urinalysis, serum electrolytes, blood urea nitrogen, serum creatinine, fasting blood glucose, lipid profile, liver function tests, and thyroid-stimulating hormone 7, 8, 9, 10
- Complete blood count (CBC) should be ordered to assess for anemia, infection, or hematologic disorders in patients presenting with fatigue 7, 9
- Urinalysis should be ordered to screen for renal disease or infection in patients presenting with fatigue 7, 9
- Serum electrolytes including calcium and magnesium should be ordered to identify electrolyte imbalances in patients presenting with fatigue 7, 9
- Blood urea nitrogen (BUN) and serum creatinine should be ordered to evaluate kidney function in patients presenting with fatigue 7, 9
- Fasting blood glucose or glycohemoglobin (HbA1c) should be ordered to screen for diabetes in patients presenting with fatigue 7, 9
- Lipid profile should be ordered to assess cardiovascular risk in patients presenting with fatigue 7, 9
- Liver function tests should be ordered to evaluate hepatic disorders in patients presenting with fatigue 7, 9
- Thyroid-stimulating hormone (TSH) should be ordered to screen for thyroid dysfunction in patients presenting with fatigue 7, 9, 10
Additional Testing Based on Clinical Context
- For cancer patients or survivors, consider evaluating disease status and performing a comprehensive assessment of contributing factors 11, 12, 13
- For patients with suspected heart failure, consider B-type natriuretic peptide (BNP) or N-terminal pro-B-type natriuretic peptide (NT-proBNP) 10, 14
Assessment Algorithm
- Quantify fatigue severity using a 0-10 numeric rating scale, with mild fatigue defined as 1-3, moderate fatigue defined as 4-6, and severe fatigue defined as 7-10 12
- Order core laboratory tests for all patients with fatigue 7, 9, 10
- For moderate to severe fatigue (score ≥4), perform a focused fatigue history, thorough medical examination, review of body systems, and mental status examination 8, 11, 12, 13
Important Considerations
- The predictive value of laboratory tests is relatively low in cancer-related fatigue, but they remain important to rule out treatable causes 12, 13
- Fatigue often coexists with other symptoms, so a multisymptom screening approach may be valuable 12, 13