Acute kidney injury (AKI) now is recognized as a systemic disease. It occurs frequently in critically ill patients and has profound effects on morbidity and mortality. Recent research efforts have shown a bidirectional interplay between AKI and the immune system. Both innate and adaptive immune responses mediate renal injury as well as recovery from AKI. Dendritic cells, monocytes/macrophages, neutrophils, T lymphocytes, and B lymphocytes all play specific roles in the development of AKI. M2 macrophages and regulatory T cells also are pivotal in controlling inflammation, tissue remodeling, and repair after AKI. Conversely, existing evidence also suggests that increased production and decreased clearance of cytokines as well as dysfunction of immune cells, in particular neutrophils, can contribute to immune dysfunction and impaired bacterial clearance during AKI. Clinical data indicate that AKI is a risk factor for infections after various forms of critical illness, including cardiac surgery, malignancies, or severe trauma. Available evidence does not suggest that standard renal replacement therapies improve outcome from AKI beyond control of fluid balance and azotemia. Thus, novel approaches likely will be necessary to prevent or treat AKIinduced dysregulation of the inflammatory response.

Background and objectives Children with nephrotic syndrome can develop life-threatening complications, including infection and thrombosis. While AKI is associated with adverse outcomes in hospitalized children, little is known about the epidemiology of AKI in children with nephrotic syndrome. The main objectives of this study were to determine the incidence, epidemiology, and hospital outcomes associated with AKI in a modern cohort of children hospitalized with nephrotic syndrome.Design, setting, participants, & measurements Records of children with nephrotic syndrome admitted to 17 pediatric nephrology centers across North America from 2010 to 2012 were reviewed. AKI was classified using the pediatric RIFLE definition.Results AKI occurred in 58.6% of 336 children and 50.9% of 615 hospitalizations (27.3% in stage R, 17.2% in stage I, and 6.3% in stage F). After adjustment for race, sex, age at admission, and clinical diagnosis, infection (odds ratio, 2.24; 95% confidence interval, 1.37 to 3.65; P=0.001), nephrotoxic medication exposure (odds ratio, 1.35; 95% confidence interval, 1.11 to 1.64; P=0.002), days of nephrotoxic medication exposure (odds ratio, 1.10; 95% confidence interval, 1.05 to 1.15; P,0.001), and intensity of medication exposure (odds ratio, 1.34; 95% confidence interval, 1.09 to 1.65; P=0.01) remained significantly associated with AKI in children with nephrotic syndrome. Nephrotoxic medication exposure was common in this population, and each additional nephrotoxic medication received during a hospitalization was associated with 38% higher risk of AKI. AKI was associated with longer hospital stay after adjustment for race, sex, age at admission, clinical diagnosis, and infection (difference, 0.45 [log]days; 95% confidence interval, 0.36 to 0.53 [log]days; P,0.001).Conclusions AKI is common in children hospitalized with nephrotic syndrome and should be deemed the third major complication of nephrotic syndrome in children in addition to infection and venous thromboembolism. Risk factors for AKI include steroid-resistant nephrotic syndrome, infection, and nephrotoxic medication exposure. Children with AKI have longer hospital lengths of stay and increased need for intensive care unit admission.

Atypical hemolytic uremic syndrome (aHUS) is a rare and complex disease resulting from abnormal alternative complement activation with a wide range of clinical presentations. Extra-renal manifestations of aHUS can involve many organ systems, including the peripheral and central nervous, gastrointestinal, cardiovascular, integumentary, pulmonary, as well as the eye. While some of these extra-renal manifestations occur in the acute phase of aHUS, some can also occur as long-term sequelae of unopposed complement activation. Extra-renal symptoms are observed in approximately 20% of patients with aHUS, with the incidence of specific organ system complications ranging from a few case reports to 50% of described patients. Careful monitoring for extra-renal involvement is critical in patients with aHUS, as prompt evaluation and management may decrease the risk of high morbidity and mortality associated with aHUS.

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