What blood investigations are needed for a thorough medical evaluation?

Essential Blood Investigations for a Thorough Medical Evaluation

A comprehensive blood workup 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

Hematology

• Complete Blood Count (CBC) - evaluates total numbers and characteristics of blood cell components, providing insights into anemia, infection, inflammation, and various hematological disorders 1, 2
  • Red blood cell count, hemoglobin, hematocrit
  • White blood cell count with differential
  • Platelet count
  • Red cell indices (MCV, MCH, MCHC, RDW)

Chemistry

• Comprehensive Metabolic Panel
  • Serum electrolytes (sodium, potassium, chloride, bicarbonate) 1
  • Additional electrolytes (calcium, magnesium) 1
  • Blood urea nitrogen (BUN) 1
  • Serum creatinine and estimated glomerular filtration rate 1
  • Liver function tests (ALT, AST, alkaline phosphatase, bilirubin) 1
  • Glucose metabolism
    • Fasting blood glucose 1
    • Glycohemoglobin (HbA1c) 1

Lipid Profile

• Total cholesterol 1
• LDL cholesterol 1
• HDL cholesterol 1
• Triglycerides 1

Endocrine Function

• Thyroid-stimulating hormone (TSH) 1
• Additional thyroid tests when indicated (T3, T4)

Urinalysis

• Physical, chemical, and microscopic examination 1
• Spot urinary albumin-to-creatinine ratio (for kidney function assessment) 1

Additional Specialized Tests

Iron Studies

• Serum iron 1
• Ferritin 1
• Transferrin saturation 1

Nutritional Assessment

• Vitamin B12 (particularly for patients on metformin) 1
• Vitamin D, calcium, and phosphorous (when clinically indicated) 1

Inflammatory Markers

• Erythrocyte sedimentation rate (ESR) - especially in younger patients 1
• C-reactive protein (CRP) when inflammation is suspected

Disease-Specific Considerations

Cardiovascular Assessment

• For patients with suspected heart failure or cardiovascular disease:
  • Cardiac biomarkers (troponin, BNP/NT-proBNP) 1
  • Electrocardiogram (ECG) should complement blood tests 1

Diabetes Management

• For patients with diabetes or suspected diabetes:
  • HbA1c 1
  • Fasting blood glucose 1
  • Lipid profile 1
  • Kidney function tests 1

Kidney Disease Evaluation

• For patients with suspected kidney disease:
  • Serum creatinine and eGFR 1
  • BUN 1
  • Electrolytes 1
  • Urinary albumin-to-creatinine ratio 1

Clinical Pearls and Caveats

• The interpretation of laboratory values should always be done in conjunction with clinical findings and patient history 3, 4
• Abnormal values should be interpreted in the context of the patient's baseline when available 5
• Certain medications can affect laboratory results (e.g., metformin may lower vitamin B12 levels) 1
• Fasting status is important for accurate interpretation of glucose and lipid profiles 1, 6
• Consider the timing of blood draws in relation to dialysis for patients with end-stage renal disease 1
• For patients on anticoagulants, coagulation tests may be necessary before invasive procedures 1

Follow-up Testing

• Frequency of repeat testing should be based on:
  • Initial findings 1
  • Chronic disease status 1
  • Medication regimens that require monitoring 1
  • Changes in clinical status 1