What laboratory tests should be ordered prior to a comprehensive medical workup?

Laboratory Tests Prior to Comprehensive Medical Workup

For a general comprehensive medical workup, order a complete blood count with differential, comprehensive metabolic panel (including electrolytes, calcium, renal and liver function tests), urinalysis, thyroid-stimulating hormone, and inflammatory markers (ESR and/or CRP) as your foundational laboratory assessment. 1, 2, 3

Core Laboratory Panel

Hematologic Assessment

• Complete blood count (CBC) with differential and platelet count to evaluate for anemia, infection, hematologic disorders, and bone marrow function 1, 2, 3
• Red cell indices including mean corpuscular volume (MCV) and red cell distribution width (RDW) to characterize anemia type 2
• Reticulocyte count when anemia is present to assess bone marrow response 2

Metabolic and Renal Function

• Comprehensive metabolic panel including 1, 2, 3:
  • Serum creatinine and blood urea nitrogen (BUN) for renal function
  • Serum electrolytes (sodium, potassium, chloride, bicarbonate)
  • Serum calcium (corrected for albumin)
  • Serum glucose or HbA1c for diabetes screening
  • Liver function tests (AST, ALT, alkaline phosphatase, bilirubin, albumin)

Inflammatory Markers

• Erythrocyte sedimentation rate (ESR) for chronic inflammatory conditions and monitoring 1, 2, 4, 5
• C-reactive protein (CRP) for acute inflammatory processes and infection 1, 2, 4, 5
  • CRP rises rapidly within 48 hours of acute inflammation and falls quickly with resolution, making it superior for acute diagnosis 4, 5
  • ESR has a longer half-life and is better for monitoring chronic conditions 4, 5
  • Use both ESR and CRP together in chronic diseases for optimal information 4, 5

Additional Core Tests

• Urinalysis to screen for renal disease, infection, or metabolic abnormalities 1, 2
• Thyroid-stimulating hormone (TSH) to screen for thyroid dysfunction 2
• Coagulation profile (PT/INR, aPTT) when bleeding risk exists or anticoagulation is planned 1

Disease-Specific Considerations

When Malignancy is Suspected

• Lactate dehydrogenase (LDH) as a prognostic marker 1
• Serum calcium (corrected) as hypercalcemia suggests malignancy 1
• Alkaline phosphatase if bone metastases are suspected 1

When Infection or Sepsis is Suspected

• Procalcitonin for rapid diagnosis of bacterial infection 1
• Lactate to assess tissue perfusion and sepsis severity 1
• Blood cultures before antibiotic administration 1

When Autoimmune Disease is Suspected

• Antinuclear antibodies (ANA) as initial screening 3, 5
• Complement levels (C3, C4) particularly for systemic lupus erythematosus 5
• Autoantibody panel based on clinical presentation 1, 3, 5

When Anemia Requires Further Evaluation

• Serum ferritin and transferrin saturation to assess iron status 2
• Vitamin B12 and folate levels to identify deficiency 2
• Haptoglobin, LDH, and indirect bilirubin if hemolysis is suspected 2

Pre-Treatment Laboratory Requirements

Before Immunosuppressive Therapy

Test for viral hepatitis B and C, and latent/active tuberculosis before initiating disease-modifying antirheumatic drugs (DMARDs) or other immunosuppressants 1

Before Thyroid Ablation Procedures

• Thyroid function tests and calcitonin are mandatory 1
• Blood type determination 1
• Hepatitis B surface antigen, hepatitis C antibodies, syphilis antibodies, HIV antibody testing 1

Before Methotrexate Therapy

• Baseline CBC with differential and platelet count, hepatic enzymes, renal function tests, and chest X-ray 6
• Monthly hematology monitoring and renal/liver function every 1-2 months during therapy 6

Important Clinical Pitfalls

Avoid These Common Errors

• Do not order bone scans routinely—only when alkaline phosphatase is elevated or bone pain is present 1
• Do not order brain imaging routinely—only when clinical signs or symptoms suggest metastases 1
• Laboratory abnormalities affect management in only 5% of fatigue cases, but remain essential to exclude treatable causes 2
• False elevations or reductions in ESR and CRP can occur due to multiple factors including age, medications, and chronic conditions 4

Timing Considerations

• Obtain coagulation studies before procedures and discontinue anticoagulants appropriately 1
• Establish IV access before procedures to facilitate contrast administration and emergency drug delivery 1
• Patients should fast 4-6 hours before procedures requiring sedation 1

Monitoring Strategy

• More frequent monitoring is indicated during dose changes, periods of increased toxicity risk (dehydration), or when using high-risk medications 6
• Persistent liver function abnormalities may precede fibrosis or cirrhosis and require evaluation even without symptoms 6