What are the lab findings for an adult patient with a history of cocaine use, presenting with symptoms of Thrombotic Microangiopathy (TMA)?

Laboratory Findings in Cocaine-Associated Thrombotic Microangiopathy

In an adult patient with cocaine use presenting with TMA, expect thrombocytopenia, microangiopathic hemolytic anemia with schistocytes, elevated LDH, decreased haptoglobin, and acute kidney injury with elevated creatinine—but critically, troponin I or T should be measured as the preferred cardiac biomarker since CK and CK-MB are frequently elevated from rhabdomyolysis rather than true myocardial injury. 1

Core Laboratory Abnormalities in Cocaine-Induced TMA

Hematologic Findings

• Thrombocytopenia is a hallmark finding, though notably 13% of TMA patients may not show significant platelet reduction 2
• Microangiopathic hemolytic anemia with schistocytes >1% on peripheral smear strongly supports TMA diagnosis 2, 3, 4
• Anemia may be absent in 38% of cases early in presentation—absence does not exclude TMA 2
• Elevated LDH from hemolysis is expected 2
• Decreased or undetectable haptoglobin from intravascular hemolysis 2

Renal Function

• Elevated creatinine indicating acute kidney injury, potentially requiring dialysis 3, 5, 4
• Hematuria is common 3
• Renal biopsy (when performed) reveals thrombotic microangiopathy with fibrinoid necrosis of arterioles and glomerular tufts 5, 4

Cardiac Biomarkers: Critical Distinction

• Troponin I and T are the preferred cardiac markers because they are more specific for myocardial injury 1, 6
• Total CK and CK-MB are frequently elevated (up to 75% of patients) due to rhabdomyolysis, increased motor activity, and skeletal muscle injury—not necessarily indicating myocardial infarction 1, 6
• Myoglobin elevation occurs from rhabdomyolysis and confounds diagnosis 1

Essential Diagnostic Testing to Determine TMA Etiology

Immediate Priority Tests

• ADAMTS13 activity and anti-ADAMTS13 antibodies must be tested immediately, as activity <10% indicates thrombotic thrombocytopenic purpura (TTP) requiring specific management 1, 2
• Antiphospholipid antibodies to identify potential antiphospholipid syndrome-associated TMA 1, 2
• PLASMIC score calculation for risk stratification—scores >5 points indicate moderate/high risk for TTP 1, 2

Cocaine Detection

• Urine benzoylecgonine (cocaine metabolite) can be detected 24-48 hours after use, or up to 22 days in chronic heavy users 1
• Standard cutoff is 300 ng/mL 1
• Self-reporting should be the primary method for establishing cocaine use, with urine testing reserved for patients unable to communicate 1

Cardiovascular Assessment

ECG Findings

• Abnormal ECG in 56-84% of cocaine-associated chest pain patients 1
• Early repolarization pattern (normal variant) occurs in 32% and can be misinterpreted 1
• ST-segment elevation occurs in 42% but does not necessarily indicate MI 1
• Only 2% have changes typical for ST-elevation MI and 6% have changes specific for acute ischemia 1

Coagulation Studies

• Increased thromboxane A2 production and platelet aggregation from cocaine's procoagulant effects 1, 7
• Reversible reduction in protein C and antithrombin III may be observed 1

Critical Pitfalls

• Schistocytes may be absent in early TMA due to low sensitivity—their absence does not exclude diagnosis 2
• Normal platelet counts do not exclude TMA in 13% of cases 2
• CK-MB elevation without troponin elevation likely represents rhabdomyolysis rather than MI 1, 6
• Delayed ADAMTS13 testing increases mortality—start plasma exchange and glucocorticoids while awaiting results in suspected TTP 1, 2