What initial blood work should be done to investigate a patient's condition?

Initial Laboratory Workup for Patient Investigation

The initial laboratory evaluation of patients 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

Hematologic Assessment

• Complete Blood Count (CBC)
  • Provides critical information about:
    • Red blood cell parameters (hemoglobin, hematocrit, indices)
    • White blood cell count with differential
    • Platelet count
  • Helps identify anemia, infection, inflammation, and hematologic disorders 2

Renal Function

• Blood Urea Nitrogen (BUN)
• Serum Creatinine
• Urinalysis
  • Essential for detecting kidney dysfunction
  • Helps assess volume status
  • Urinalysis can reveal proteinuria, hematuria, or signs of infection 1

Electrolyte Panel

• Sodium, Potassium, Chloride, Bicarbonate
• Calcium and Magnesium
  • Critical for detecting electrolyte imbalances that may indicate endocrine, renal, or cardiac disorders
  • Particularly important when evaluating patients with suspected heart failure or dehydration 1

Metabolic Assessment

• Fasting Blood Glucose/Glycohemoglobin (HbA1c)

  • Screens for diabetes and impaired glucose metabolism
  • Essential for metabolic evaluation 1

• Lipid Profile

  • Total cholesterol, LDL, HDL, triglycerides
  • Important for cardiovascular risk assessment 1

Hepatic Function

• Liver Function Tests
  • AST, ALT, alkaline phosphatase, bilirubin, albumin
  • Helps identify hepatic disorders that may be primary or secondary to systemic disease 3

Endocrine Assessment

• Thyroid-Stimulating Hormone (TSH)
  • Essential screening for thyroid dysfunction
  • Both hyperthyroidism and hypothyroidism can present with various systemic symptoms 1

Additional Considerations

Cardiac Biomarkers

• Consider adding cardiac biomarkers (troponin, BNP/NT-proBNP) when cardiac pathology is suspected
• BNP/NT-proBNP is particularly useful when heart failure is suspected 1

Inflammatory Markers

• C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) may be added when inflammatory or infectious processes are suspected

Special Populations

Suspected Heart Failure

• For patients with suspected heart failure, include BNP or NT-proBNP testing
• Consider additional cardiac workup including ECG and echocardiography 1

Suspected Malignancy

• In cases where malignancy is suspected, consider tumor markers appropriate to the suspected primary site
• For suspected hematologic malignancies, peripheral blood smear examination should be included 1

Important Caveats

• Laboratory testing should be guided by the clinical presentation and suspected diagnoses
• Abnormal test results should be interpreted in the context of the patient's clinical picture
• Initial laboratory tests may need to be followed by more specialized testing based on preliminary findings
• Volume status assessment through orthostatic blood pressure measurements should accompany laboratory evaluation when hypovolemia or hypervolemia is suspected 4

Remember that while these tests provide valuable diagnostic information, they must be interpreted alongside a thorough clinical assessment. Isolated laboratory abnormalities without clinical correlation may lead to unnecessary additional testing and potential harm.