What labs should be ordered for a patient with traumatic injury?

Laboratory Tests for Trauma Patients

For patients with traumatic injury, a comprehensive laboratory panel should include complete blood count, coagulation studies, blood gases with lactate, and organ-specific tests based on suspected injuries. The laboratory evaluation is essential for assessing the extent of bleeding, tissue hypoperfusion, and potential coagulopathy to guide resuscitation and treatment decisions.

Core Laboratory Tests

Blood Count and Bleeding Assessment

• Complete blood count (CBC) with hemoglobin/hematocrit measurements should be obtained, with repeated measurements to detect ongoing bleeding, as initial values may be normal despite significant blood loss 1
• Platelet count should be maintained >100,000/mm³ in trauma patients with TBI or ongoing bleeding 1
• Single hemoglobin/hematocrit measurements should not be used in isolation as they may mask early bleeding 1

Metabolic and Perfusion Assessment

• Serum lactate measurement is recommended as a sensitive marker of tissue hypoperfusion and shock severity 1
• Base deficit from arterial blood gas analysis provides an indirect estimation of global tissue acidosis due to impaired perfusion 1
• Serial lactate measurements provide valuable prognostic information; normalization within 24 hours is associated with improved survival 1

Coagulation Studies

• Early, repeated measurements of PT, APTT, fibrinogen, and platelet count should be performed to detect trauma-induced coagulopathy 1
• Approximately 25-35% of trauma patients present with coagulopathy on admission, which is associated with increased mortality 2, 3
• Viscoelastic hemostatic assays (TEG/ROTEM) should be used when available to better characterize coagulopathy and guide hemostatic therapy 1, 2

Specific Injury Assessment

Thoracoabdominal Injuries

• For suspected thoracoabdominal injuries, laboratory tests should include 1:
  • Liver enzymes (AST, ALT)
  • Pancreatic enzymes (amylase, lipase)
  • Urinalysis
  • Renal function tests (BUN, creatinine)
• Cardiac injury markers (troponin, CK-MB) should be considered in cases of chest trauma 1

Traumatic Brain Injury

• In patients with TBI, coagulation studies are particularly important as coagulopathy is associated with progression of intracranial bleeding 1
• Ionized calcium should be monitored and corrected in bleeding trauma patients 1

Differential Diagnosis for Specific Populations

• In cases where child abuse or metabolic bone disease is suspected, additional tests may include 1:
  • Serum calcium, phosphorus, and alkaline phosphatase
  • Parathyroid hormone and 25-hydroxy-vitamin D
  • Serum copper and ceruloplasmin

Timing and Interpretation

• Initial laboratory tests should be obtained as soon as possible upon arrival 1
• Results should be available rapidly to guide resuscitation and treatment decisions 1
• Serial measurements provide more valuable information than single measurements 1
• Abnormal coagulation tests are increasingly frequent with higher injury severity and are associated with excess mortality even at values below conventional transfusion triggers 3

Pitfalls and Caveats

• Initial normal hemoglobin/hematocrit values may mask significant bleeding due to the time required for fluid shifts from interstitial space 1
• Resuscitation fluids can dilute blood components and affect laboratory values, particularly hemoglobin/hematocrit 1
• Standard coagulation tests (PT/APTT) may not fully reflect in vivo coagulation status in trauma patients 2, 4
• Viscoelastic tests provide a more comprehensive assessment of coagulation but may not be available in all settings 2
• Hypothermia, acidosis, and hypocalcemia can exacerbate coagulopathy and should be corrected 4

Laboratory testing in trauma should be guided by the clinical presentation, suspected injuries, and available resources, with the understanding that serial measurements and trending of values often provide more valuable information than isolated results.