Initial Laboratory Tests for Patients with Unknown Conditions
For patients presenting with unknown conditions, obtain a complete blood count, serum electrolytes and glucose, liver function tests, renal function (BUN/creatinine), and urinalysis as the foundational laboratory workup. 1
Core Laboratory Panel
The initial laboratory evaluation should include:
Complete blood count (CBC) to assess for infection, inflammation, anemia, or cytopenias that may indicate underlying hematologic, infectious, or systemic disease 1, 2
Serum electrolytes and glucose to evaluate for metabolic derangements, dehydration, diabetes, or endocrine dysfunction 1, 2
Renal function tests (BUN/creatinine) to assess kidney function and calculate estimated glomerular filtration rate (eGFR) 3, 2
Liver function tests to rule out hepatic causes of symptoms and assess for liver dysfunction 1, 3
Urinalysis to evaluate hydration status, rule out urinary tract pathology, and screen for metabolic abnormalities 1
Additional First-Tier Tests Based on Clinical Context
Beyond the core panel, consider these additional tests when clinically indicated:
Inflammatory markers (C-reactive protein, procalcitonin) if systemic infection or sepsis is suspected 3
Serum lipase if abdominal pain or vomiting suggests pancreatitis 1
Calcium and magnesium to evaluate electrolyte abnormalities that may affect multiple organ systems 2
Thyroid function tests (TSH) to screen for thyroid dysfunction, which can present with diverse symptoms 2
Hemoglobin A1c to investigate undetected diabetes mellitus, particularly if glucose abnormalities are present 3
Symptom-Directed Laboratory Additions
For patients with specific presenting symptoms, tailor the laboratory workup accordingly:
Vomiting patients: Add serum lipase to the core panel to assess for pancreatitis 1
Suspected neurological conditions: Include creatine kinase (CK) to evaluate for muscle involvement, though this is nonspecific 4
Suspected infection/sepsis: Add blood gas analysis, procalcitonin, and blood cultures 3
Suspected occult malignancy: Consider alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and calcium levels 3
Common Pitfalls to Avoid
Do not order extensive laboratory panels indiscriminately. Basic laboratory tests are only indicated when clinical presentation suggests specific metabolic, infectious, or systemic causes 3. Ordering tests without clinical justification increases false-positive results and unnecessary follow-up testing.
Avoid using standard reference ranges without considering disease-specific contexts. Interpretation must account for the clinical scenario and patient characteristics 2.
Do not delay urgent interventions while awaiting laboratory results. In emergent situations such as suspected Fournier's gangrene or severe sepsis, treatment should begin immediately after blood draws are obtained 3.
Risk Stratification Considerations
The laboratory workup should be guided by the patient's risk profile:
High-risk patients (elderly, immunocompromised, multiple comorbidities) warrant more comprehensive initial testing including inflammatory markers and organ function panels 3
Low-risk patients with isolated symptoms may require only the core laboratory panel unless clinical examination suggests specific organ system involvement 3