Diagnostic Laboratory Testing for Acute Limb Ischemia
For acute limb ischemia, obtain the following laboratory tests immediately: complete blood count, platelet count, fasting blood glucose or hemoglobin A1c, creatinine with estimated glomerular filtration rate, coagulation studies (aPTT and INR), fasting lipid profile, urinalysis, troponin, and a 12-lead electrocardiogram. 1
Essential Hematologic and Biochemical Tests
The ACC/AHA guidelines specify a comprehensive laboratory panel for patients with critical limb ischemia that directly applies to acute presentations 1:
- Complete blood count and platelet count - Essential to assess for anemia, polycythemia, or thrombocytosis that may contribute to thrombotic events 1
- Coagulation studies (aPTT, INR) - Critical before initiating anticoagulation therapy and to identify underlying coagulopathies 1
- Renal function (creatinine, eGFR) - Mandatory before contrast imaging (CTA or angiography) to assess nephropathy risk, particularly important as many ALI patients have chronic kidney disease 1
- Glucose metabolism markers (fasting glucose or HbA1c) - Identifies diabetes, a major risk factor for both atherosclerotic disease and poor outcomes 1
- Fasting lipid profile - Documents dyslipidemia requiring aggressive management post-revascularization 1
- Urinalysis - Screens for glycosuria and proteinuria indicating diabetic nephropathy 1
Cardiac Evaluation
Obtain a 12-lead ECG immediately to identify atrial fibrillation, which is the most common embolic source causing acute limb ischemia, particularly in upper extremity presentations 1, 2. The ECG also detects evidence of myocardial infarction or left ventricular hypertrophy that increases perioperative risk 1.
Troponin measurement is indicated as part of the initial workup to assess for concurrent acute coronary syndrome, given the high prevalence of coronary artery disease in this population 1.
Source Evaluation for Embolic Disease
If embolic etiology is suspected (particularly with atrial fibrillation, sudden onset without prior claudication, or upper extremity involvement), additional cardiac imaging may be warranted 1:
- Transthoracic echocardiography (TTE) can identify cardiac thrombus, valvular disease, or areas of dysfunction 1
- Transesophageal echocardiography (TEE) provides superior visualization of the left atrium and is useful when TTE is indeterminate, though it should not delay revascularization 1
Critical Timing Considerations
These laboratory tests should be obtained simultaneously with—not instead of—immediate imaging and anticoagulation. The ACC/AHA emphasizes that patients with acute limb ischemia and a salvageable extremity require emergent evaluation and prompt revascularization 1. Laboratory abnormalities should not delay definitive treatment when the limb is immediately threatened (Rutherford Category IIb) 1, 3.
Common Pitfalls to Avoid
- Do not delay anticoagulation while waiting for coagulation studies unless there is obvious active bleeding 1, 4
- Do not withhold contrast imaging in patients with chronic kidney disease when limb viability is threatened—the benefit of limb salvage outweighs nephropathy risk 4, 5
- Do not order extensive cardiac workup that delays revascularization; echocardiography is not part of the initial emergency workup unless it changes immediate management 1
- Recognize that normal laboratory values do not exclude ALI—diagnosis is primarily clinical and imaging-based 1, 6