What are UPCR (Urine Protein-to-Creatinine Ratio) and UACR (Urine Albumin-to-Creatinine Ratio) in a patient with a history of cocaine use and suspected Thrombotic Microangiopathy (TMA)?

UPCR and UACR in Nephrology

UPCR (Urine Protein-to-Creatinine Ratio) and UACR (Urine Albumin-to-Creatinine Ratio) are spot urine tests that quantify proteinuria and albuminuria respectively, eliminating the need for 24-hour urine collections. 1

Definitions and Clinical Use

UACR (Urine Albumin-to-Creatinine Ratio):

• Measures albumin excretion specifically, expressed as mg of albumin per gram of creatinine 1
• Values >30 mg/g are considered abnormal and indicate kidney damage 1
• The American Heart Association recommends UACR screening for all patients with cardiovascular disease to detect chronic kidney disease 1
• More sensitive for early kidney disease detection, particularly in diabetic nephropathy and hypertensive kidney disease 1

UPCR (Urine Protein-to-Creatinine Ratio):

• Measures total protein excretion, including albumin and other proteins 1
• Used to quantify proteinuria in established kidney disease 1
• Provides broader assessment than UACR when non-albumin proteinuria is suspected 1

Relevance in Cocaine-Associated TMA

In your patient with cocaine use and suspected thrombotic microangiopathy, these tests serve critical diagnostic and monitoring functions:

Diagnostic Value:

• Both UPCR and UACR help identify kidney involvement in cocaine-induced TMA 2, 3, 4
• Cocaine-induced TMA presents with microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury, where proteinuria assessment guides severity 2, 3
• Elevated proteinuria indicates glomerular endothelial injury from cocaine's vasoconstrictive and procoagulant effects 2, 5

Pathophysiology Context:

• Cocaine causes endothelial injury, vasoconstriction, and platelet activation leading to thrombotic microangiopathy 2, 5
• The resulting glomerular ischemia and thrombotic microangiopathy manifest as proteinuria detectable by UPCR/UACR 2, 3
• Cocaine metabolites are excreted in urine, and patients with hepatic dysfunction have prolonged exposure risk 1

Screening Recommendations

The American Heart Association recommends (Class IIa):

• Screen all cardiovascular disease patients with estimated GFR and UACR 1
• GFR <60 mL/min/1.73m² is abnormal (Class I recommendation) 1
• UACR >30 mg/g indicates kidney damage (Class IIa recommendation) 1

Clinical Pitfalls

Important caveats in cocaine-associated kidney injury:

• Rhabdomyolysis from cocaine can elevate total creatine kinase and myoglobin, confounding assessment 1, 6, 4
• Acute kidney injury may occur with or without rhabdomyolysis in cocaine users 6, 4
• Multiple mechanisms of kidney injury exist: rhabdomyolysis, TMA, vasculitis, acute interstitial nephritis, and renal infarction 4
• Malignant hypertension-associated TMA is a rare but critical complication requiring immediate recognition 3
• Renal biopsy may show thrombotic microangiopathy with fibrinoid necrosis and glomerular ischemia 2, 3