What does it mean when a patient with a history of cocaine use and suspected Thrombotic Microangiopathy (TMA) has their urine spun when they provide a sample?

What "Spinning Urine" Means in Clinical Practice

"Spinning urine" refers to centrifuging a urine sample to separate cellular elements and sediment from the liquid supernatant, which is a standard laboratory procedure performed to examine urine sediment microscopically for red blood cells, white blood cells, casts, and other cellular debris—particularly important when evaluating for thrombotic microangiopathy (TMA) or other kidney pathology. 1

Purpose in TMA Evaluation

When a patient with suspected TMA provides a urine sample, spinning the urine serves several critical diagnostic functions:

Detection of Kidney Injury Markers

• Microscopic examination of spun urine sediment identifies red blood cell casts, which are pathognomonic for glomerular injury and help confirm TMA-related kidney involvement 1
• The presence of proteinuria, microscopic hematuria, and red cell casts in the sediment are key indicators that warrant kidney biopsy consideration 1
• Urine sediment analysis can reveal tubular epithelial cells and granular casts suggesting acute tubular injury from cocaine-induced rhabdomyolysis 2, 3

Specimen Validity Assessment in Cocaine Users

• Measuring urine creatinine concentration (which requires spinning to separate sediment) determines specimen validity—creatinine between 2-20 mg/dL indicates a dilute specimen that may produce false-negative drug screening results 4, 5
• Specimens with creatinine ≤2 mg/dL should be considered substituted and treated as positive results, indicating serious tampering 4
• Dilution lowers drug metabolite concentrations below screening cutoff values, causing false-negative results despite actual drug use 5

Clinical Context for Cocaine-Associated TMA

Why Urine Analysis is Critical

• Cocaine-induced TMA presents with thrombocytopenia (though 13% may not show significant platelet reduction), microangiopathic hemolytic anemia, and acute kidney injury requiring immediate urine sediment examination 6, 7
• Kidney biopsy should be considered when there is persistent proteinuria ≥0.5 g/24 hours or unexplained decrease in GFR, but initial urine sediment analysis guides this decision 1
• Cocaine causes widespread kidney pathology including glomerular, tubular, vascular and interstitial injury, making urine sediment examination essential for characterizing the injury pattern 2

Pathophysiologic Mechanisms Detected

• Cocaine-mediated endothelial injury and platelet activation cause thrombotic microangiopathy with fibrinoid necrosis of arterioles and glomerular tufts visible on biopsy, but initial detection relies on urine sediment findings 7, 8
• Complement activation (reduced C3 with normal C4) may contribute to cocaine-induced TMA pathogenesis, and urine sediment abnormalities prompt this testing 9
• Rhabdomyolysis from cocaine (present in 50-60% of cases) produces myoglobin casts visible in spun urine sediment 2, 3

Critical Pitfalls to Avoid

Drug Testing Interpretation

• Never dismiss clinical suspicion of cocaine use based solely on a negative urine drug screen from a dilute specimen—the dilution may mask substances present at low concentrations 4, 5
• If the specimen tests positive for any substance but is dilute, report it as "positive and dilute" because other drugs present at lower concentrations may have been missed 4
• Consider observed collection if intentional dilution is suspected, and use first-morning specimens which typically yield adequate concentration 4

Diagnostic Workup Requirements

• Testing ADAMTS13 activity immediately is essential, as activity <10% indicates thrombotic thrombocytopenic purpura (TTP) requiring plasma exchange, not just supportive care 6
• Test antiphospholipid antibodies to identify antiphospholipid syndrome-associated TMA, as TMA lesions should prompt aPL testing 1, 6
• CK-MB elevation without troponin elevation likely represents rhabdomyolysis rather than myocardial infarction—troponin I or T are the preferred cardiac biomarkers 6

Clinical Decision-Making

• Delayed ADAMTS13 testing increases mortality—start plasma exchange and glucocorticoids while awaiting results in suspected TTP 6
• Drug testing provides only limited information and should supplement, not replace, clinical assessment obtained through history and physical examination 4
• Serial testing over time is more reliable than a single result, as patients with serious substance use disorders will eventually produce multiple positive results 5