Measuring ADAMTS13 Helps Differentiate aHUS From Similar Diseases in Report

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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The case of a woman who developed atypical hemolytic uremic syndrome (aHUS) during pregnancy was described in a recent report, which highlights the need to measure the levels of the ADAMTS13 enzyme to differentiate aHUS from similar conditions.

The report, “A Case of Atypical Hemolytic Uremic Syndrome in a Pregnant Patient,” was published in the journal Cureus.

A team led by researchers at BronxCare Health System in New York detailed the case of a 36-year-old woman with a medical history of asthma and pulmonary embolism (blood clots in the lungs), who went to the emergency room in her 36th week of pregnancy due to premature rupture of membranes. This happens when the amniotic sac breaks open before labor begins. An emergency cesarean section was then performed to deliver the baby.

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Following surgery, the patient experienced a sudden drop in the levels of hemoglobin — the protein in red blood cells that is responsible for transporting oxygen through the bloodstream — and platelets, which are cell fragments involved in blood clotting. She received four units of packed red blood cells, but this did little to improve her condition.

Additional diagnostic tests, including a blood smear and imaging that suggested internal bruising, led clinicians to suspect she might have a thrombotic microangiopathy (TMA) — a group of disorders that also includes aHUS and is characterized by the destruction of red blood cells and platelets.

The patient received several additional transfusions of plasma, the liquid noncellular part of blood, and/or blood cells, to little effect. Notably, she had high levels of ADAMTS13 (81%), indicating she did not have a TMA called thrombocytopenic purpura (TTP), in which the enzyme’s activity is severely reduced.

“The key differentiator of atypical HUS from thrombotic thrombocytopenic purpura (TTP) is the ADAMTS 13 activity level. ADAMTS 13 activity level is mostly [less than] 5% in TTP and [greater than] 5–10% in atypical HUS,” the researchers wrote.

Per American Society of Hematology guidelines, with normal ADAMTS13 levels and since blood transfusions were ineffective, the patient was started on Soliris (eculizumab), an approved treatment for aHUS that works by blocking the activity of part of the immune system called the complement cascade. This led to a marked improvement in her clinical status and laboratory parameters, confirming the diagnosis of aHUS.

“The diagnosis of atypical HUS can be challenging as the classic triad of microangiopathic hemolytic anemia [red blood cell destruction], thrombocytopenia [low platelet counts], and acute kidney injury can be seen in all [TMAs], thus careful clinical and laboratory assessment is required to establish the diagnosis,” the researchers concluded.