Acute renal failure is prevalent in patients with thrombotic thrombocytopenic purpura associated with low plasma ADAMTS13 activity: reply

Abstract

We read carefully the comments from Dr Bentley and Dr Rodgers on our recent article. However, multiple erroneous assertions are evident. First, they state that we have reported stages of acute kidney injury (AKI) and not absolute values: however, median creatinine values are reported in Table 3 and Figure 3. As shown in our study, median creatinine values at admission are 1.6 [1.2–2.3] mg dL−1. Second, they state that 25% of thrombotic thrombocytopenic purpura (TTP) patients in our cohort required renal replacement therapy. However, Figure 1 and Table 3 show that 14 patients required renal replacement therapy. This represents 25% of TTP‐induced AKI patients but not 25% of the entire cohort. In fact, the percentage of patients requiring renal replacement therapy in all TTP patients amounts to 15% in our study. Third, the aim of our study was not to compare AKI in hemolytic‐uremic syndrome patients and TTP patients, and we did not intend to call into question whether AKI is more severe in those with other thrombotic microangiopathies (TMAs) compared with TTP patients. However, we aimed to describe the incidence, characteristics, and outcomes of AKI specifically in TTP patients. Definition and staging of AKI were set according to the KDIGO 2012 guidelines 1.Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGOclinical practice guideline for the evaluation and management of chronic kidney disease.Kidney Int Suppl. 2012; 2013: 1-150Google Scholar. The higher prevalence of AKI in our study, compared with the studies mentioned by Dr Bentley and Dr Rodgers, is mainly due to the fact that we used these widely accepted new operational AKI definitions. Before these recommendations, definitions of AKI were more restrictive; thus, AKI of a lesser degree may have been overlooked. For example, in the study by Vesely et al. 2.Vesely S.K. George J.N. Lammle B. Studt J.D. Alberio L. El‐Harake M.A. Raskob G.E. ADAMTS13 activity in thrombotic thrombocytopenic purpura‐hemolytic uremic syndrome: relation to presenting features and clinical outcomes in a prospective cohort of 142 patients.Blood. 2003; 102: 60-8Crossref PubMed Scopus (572) Google Scholar mentioned by Dr Bentley and Dr Rodgers, acute renal failure is defined by either an increasing serum creatinine of 0.5 mg dL−1 per day for 2 consecutive days or a serum creatinine of 4 mg dL−1 plus dialysis. The term AKI is intended to encompass the entire spectrum of the syndrome, from minor impairment in renal function to the need for renal replacement therapy. AKI is more than just acute renal failure; it encompasses the entire spectrum from severe to less severe conditions. There is now substantial evidence from clinical studies that both short‐term and long‐term outcomes are adversely affected by AKI, and even small changes in serum creatinine concentrations are associated with a substantial increase in the risk of death 3.Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-70Crossref PubMed Scopus (2509) Google Scholar. We then believe that, even if AKI is less severe in TTP patients compared with those with other TMAs, TTP associated with renal involvement should not be neglected: urinalysis and renal function should be monitored during remission in order to identify a subset of patients who will require a consultation with a nephrologist. Finally, the authors’ assertion regarding possible diagnostic errors is unacceptable given that all diagnoses were based on universally approved criteria: (i) thrombopenia, (ii) microangiopathic hemolytic anemia with schizocytes and negative direct Coombs test, (iii) signs of organ ischemia, and (iv) severe ADAMTS13 deficiency 4.Scully M. Hunt B.J. Benjamin S. Liesner R. Rose P. Peyvandi F. Cheung B. Machin S.J. Guidelines on the diagnosis and management of thrombotic thrombocytopenic purpura and other thrombotic microangiopathies.Br J Haematol. 2012; 158: 323-35Crossref PubMed Scopus (539) Google Scholar. Taken together, their numerous gross assumptions and misinterpretations regarding our work lend no support to the authors’ conclusion with respect to our diagnostic workup and therapeutic management. The authors state that they have no conflict of interest.