A disintegrin and metalloproteinase with thrombospondin type 1 motif 13 (ADAMTS13) is a gene that provides instructions for an enzyme that helps your body regulate blood clotting. Too little (≤5%) ADAMTS13 may indicate thrombotic thrombocytopenic purpura (TTP) rather than atypical-HUS.

The complement system is a part of the immune system that helps protect your body from foreign substances such as bacteria or other infections. The complement system is made up of a group of proteins found in the blood.

Creatinine is a chemical waste product generated by your muscles and is filtered through your kidneys. Too much creatinine in the blood (0.7 to 1.3 mg/dL for men, 0.6 to 1.1 mg/dL for women) can signify impaired kidney function or kidney disease.

The estimated glomerular filtration rate (eGFR) is a calculation that measures how well your kidneys are filtering toxins and waste from your blood.

Hemolysis is the breakdown of red blood cells in the body.

Lactate dehydrogenase (LDH) is an enzyme that is found in almost all of your body’s cells and is released into your blood when cells are damaged or destroyed. Elevated LDH can be an indicator of hemolysis.

Platelets (or thrombocytes) are fragments of cells whose function is to help your blood clot to stop bleeding.

Red blood cells (or erythrocytes) deliver oxygen from your lungs to the rest of your body. They also transport carbon dioxide from your body’s tissues back to your lungs, where it is exhaled.

A schistocyte is a fragment of a damaged or injured red blood cell.

Thrombotic microangiopathy (TMA) is a group of medical disorders that results in clots and inflammation in various small blood vessels throughout the body. This results in injury to organs, such as the kidneys.

Thrombotic thrombocytopenic purpura (TTP) is a kind of TMA (see above). TTP is a rare blood condition that can cause blood clots that may lead to serious medical problems.

A trigger is a precipitating event that causes the onset of another condition. Triggers that may cause the symptoms of atypical-HUS include infections, certain medications, being pregnant, or having another condition, such as malignant hypertension.