aHUS (atypical hemolytic uremic syndrome) is a rare disease that causes too many blood clots to form in your blood vessels. Because these blood clots block regular blood flow to your kidneys, your kidneys are not able to get rid of waste in your body as well as they should. Over time, your kidneys become damaged, which can lead to kidney failure.

Besides kidney damage, the signs of aHUS include low red blood cell and platelet count.  Most people with aHUS have all three signs of the disease; kidney damage, low red blood cell and low platelet count, but not everyone does.

The symptoms of aHUS usually happen in flare-ups. Flare-ups of aHUS are often started by a trigger in your body. Some flare-ups of aHUS can be mild, and will not affect your kidneys. During a severe flare-up, your kidneys may be damaged and can fail.

It is also possible to have chronic aHUS, meaning you have symptoms of the disease all the time instead of only during flare-ups.