What labs should be checked for a patient with a suspected type B aortic dissection extending to the iliac arteries?

Laboratory Tests for Type B Aortic Dissection Extending to Iliac Arteries

For patients with suspected type B aortic dissection extending to the iliac arteries, a comprehensive laboratory panel should include complete blood count, comprehensive metabolic panel, coagulation studies, D-dimer, cardiac biomarkers, and blood type and screen. 1

Initial Laboratory Assessment

• Complete blood count (CBC) - To assess for anemia from blood loss and leukocytosis which may indicate inflammatory response 1
• Basic metabolic panel - To evaluate renal function which may be compromised due to renal artery involvement 1
• Coagulation profile (PT/INR, PTT) - Essential for preoperative screening if surgical intervention becomes necessary 1
• Blood type and screen - Critical for potential emergency transfusion requirements 1
• D-dimer - Highly sensitive (94%) marker for acute aortic dissection, though specificity is variable (40-100%) 1
• Cardiac biomarkers (Troponin T/I, CK, myoglobin) - To rule out myocardial infarction and assess for cardiac involvement 1

Specific Markers for Organ Ischemia

• Lactate dehydrogenase (LDH) - Elevation indicates tissue damage and may suggest involvement of the celiac artery (seen in approximately 8% of cases) 1
• Liver function tests - To assess for hepatic ischemia if celiac trunk is compromised 1
• Creatinine and BUN - Critical for monitoring renal function, especially with potential renal artery involvement 1
• C-reactive protein (CRP) - Often elevated in aortic dissection as an acute phase reactant 1

Important Considerations

• D-dimer testing is most useful in low-risk patients but should not delay imaging in high-risk patients 1
• Negative D-dimer results have been reported in cases of intramural hematoma without intimal flap, so caution is warranted 1
• Laboratory findings may show mild-to-moderate leukocytosis and slight elevations of bilirubin due to the large wound surface and hematoma 1
• Smooth muscle myosin heavy chain may be elevated in acute dissection 1

Laboratory Testing Algorithm

1. For unstable patients: Obtain immediate blood samples for CBC, metabolic panel, coagulation studies, and blood type and screen while simultaneously arranging for definitive imaging 1, 2

2. For stable patients:

   • Low clinical probability: D-dimer testing may help rule out dissection if negative 1
   • Intermediate clinical probability: D-dimer plus standard laboratory panel 1
   • High clinical probability: Complete laboratory panel without waiting for D-dimer results; proceed directly to imaging 1

Pitfalls to Avoid

• Do not delay definitive imaging in high-risk patients while waiting for laboratory results 1
• Do not rely solely on D-dimer to rule out aortic dissection in high-risk patients 1
• Be aware that normal laboratory values do not exclude aortic dissection 1
• Remember that iliac artery involvement may present with Leriche's syndrome (pulse loss in both legs) which can be painless 1

Laboratory testing plays a supportive role in the diagnosis of aortic dissection, with imaging studies (CT, MRI, or transesophageal echocardiography) being the definitive diagnostic modalities 3, 2.