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Hemolytic Uremic Syndrome: A Brief Overview

January 20, 2025

Thrombotic microangiopathies (TMAs) are a group of disorders that cause end organ damage and include hemolytic uremic syndrome (HUS), thrombotic thrombocytopenic purpura (TTP), and disseminated intravascular coagulopathy (DIC). HUS, classified into primary and secondary types, mostly affects the kidneys. HUS is the main cause of acute kidney injury (AKI) in children, producing significant morbidity and mortality.

Drs Fraustro and Clemente at the Nicklaus Children’s Hospital in Miami, Florida, have coauthored the article An Overview of Pediatric Hemolytic Uremic Syndrome, published in the January 2025 issue of Pediatrics in Review. The authors present a 4-year-old girl with HUS secondary to Streptococcus pneumoniae infection. Using this case as a backdrop, Drs. Fraustro and Clemente describe TMAs and HUS classification, epidemiology and pathogenesis, clinical presentation, differential diagnosis, management, and prognosis.

The key takeaways from the article are as follows:

HUS was historically classified based on etiology as “diarrhea positive”—or typical—and “diarrhea negative”—or atypical. This classification is now changed to primary and secondary, based on pathophysiology. Primary HUS is due to a disorder of complement regulation likely from a genetic predisposition in contrast to secondary HUS, which is most likely from an infection. The most likely cause of secondary HUS in the US is infection from Shiga toxin-producing bacteria. The authors describe the initial clinical presentation to be nonspecific, with significant variability in systemic progression.

HUS is characterized by the classical triad of hemolytic anemia, thrombocytopenia, and AKI. The diagnostic approach requires testing for hemolysis and assessing renal, cardiac, pulmonary, neurologic, and gastrointestinal function. TTP should be ruled out as this condition requires immediate initiation of plasmapheresis.

Patients in both primary and secondary HUS may have low complement levels.  If no infectious cause is found, primary HUS should be suspected and genetic workup should be initiated. Other serious diagnoses such as TTP and DIC should be ruled out.

The management of HUS is fluid management. Packed red blood cells may be needed, and platelet transfusions are only indicated if there is bleeding. Antibiotics are not indicated in HUS caused by Escherichia coli; the only notable exception is pneumococcal infection. For primary HUS, terminal complement blocking agent (anti-C5) needs to be given, especially if kidney function tests are deteriorating despite fluid resuscitation. Management should be done in conjunction with a pediatric hematologist and nephrologist.

The prognosis for HUS is usually good if there is early recognition and prompt treatment with intravenous fluids, and mortality is less than 5%, occurring predominantly in patients with neurological complications. Patients may need dialysis during the acute phase of illness and in the long term. 50% of patients are left with some kidney damage and will need long-term follow up to monitor kidney function and possible development of hypertension.

 

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