Proteinuria in patients with thrombotic thrombocytopenic purpura

The kidney is a target organ in thrombotic thrombocytopenic purpura (TTP), but the pattern of proteinuria has been poorly described. We retrospectively analyzed proteinuria in all 59 patients with a diagnosis of TTP on their discharge summary from 2000 to 2009. Urinalysis was obtained in 89% of cases; in those, proteinuria was detected by urine dipstick in 85%. In patients with dipstick proteinuria, quantification (grams per day or grams per gram creatinine) was performed in only 34% and ranged from 0.16 grams to 8.0 grams. Patients with larger amounts of proteinuria had more severe acute renal failure, were more likely to receive a renal biopsy, and were more likely to undergo dialysis. When analysis was restricted to patients with highly depressed activity levels of the metalloprotease ADAMST13, proteinuria tended to be low grade and transient, and renal insufficiency was mild. Proteinuria is common in thrombotic microangiopathies and may be nephrotic-range, but TTP with depressed ADAMST13 activity is characterized by less proteinuria and less severe renal dysfunction. Although this study presents the largest sample of proteinuria quantification ever reported for TTP, quantification was performed in only one-third of cases.