How Does My Doctor Know I Have aHUS?

Since atypical hemolytic uremic syndrome (aHUS) is rare and has symptoms similar to those of other disorders, it can sometimes be challenging for a doctor to make a correct diagnosis. Thus, your doctor will likely use a number of different tests to determine whether you have aHUS.

The rare disorder is characterized by the formation of abnormal blood clots in small blood vessels, which can lead to organ damage, especially in the kidneys.

The following details the diagnostic criteria your doctor will use to determine if you have aHUS, and some of the tests that he or she will conduct.

What are the diagnostic criteria your doctor will use?

The Joint Committee of the Japanese Society of Nephrology and the Japan Pediatric Society (JSN/JPS) proposed several criteria for a definitive diagnosis of aHUS. Your doctor will check whether you have acute kidney injury, thrombocytopenia — low levels of platelets — and hemolytic anemia, characterized by the destruction of red blood cells.

Hemolytic anemia

In aHUS, red blood cells may burst when they attempt to squeeze past the abnormal blood clots that form in the small blood vessels. The body produces more red blood cells all the time. However, if the rate of destruction outpaces the replacement rate, this could lead to low numbers of red blood cells or anemia.

Hemolytic anemia is defined by the Joint Committee of the JSN/JPS as blood hemoglobin levels of less than 10 g/dL. Hemoglobin is the molecule that carries oxygen in red blood cells. A decrease in the amount of hemoglobin also can help your doctor know whether your red blood cell numbers are low.

Thrombocytopenia

Platelets are small cell fragments present in your blood that are responsible for forming clots to stop bleeding. In people with aHUS, platelets are involved in the formation of clots in the small blood vessels, which reduces their numbers in the body’s circulation. A platelet count lower than 150,000 per microliter is defined as thrombocytopenia.

Acute kidney injury

The formation of blood clots in the kidneys can make it harder for them to filter toxins out of the blood and also lead to damage. Over time, this damage can lead to kidney failure. There are a number of diagnostic tests that your doctor can perform to look for acute kidney injury.

What other diseases will your doctor check for?

There are other diseases such as Shiga-like toxin-producing E.coli-HUS (STEC-HUS) or thrombotic thrombocytopenic purpura (TTP) that may cause symptoms similar to aHUS. Your doctor will check whether your symptoms may be due to these diseases.

STEC-HUS

Infections with certain types of bacteria can cause hemolytic uremic syndrome (HUS). These bacteria produce Shiga toxins or Shiga-like toxins that lead to HUS symptoms.

The most common form of this HUS, STEC-HUS, is caused by E. coli infections. STEC-HUS was previously called diarrhea+HUS (D+HUS) because patients also had diarrhea. Since aHUS can sometimes also cause diarrhea, your physician will likely perform tests to look for the presence of Shiga-like toxins in your body to help differentiate aHUS from STEC-HUS.

TTP

TTP also leads to the formation of blood clots in the small blood vessels. However, another mechanism regulates this. Patients with TTP have low levels of an enzyme called ADAMTS13, which causes platelets to clump together and form the blood clots seen in 34-91% of TTP cases. Your physician will check your levels of ADAMTS13 to see if it is low in order to help rule out TTP.

Less common diseases

Other less common disorders that cause clot formation in the small blood vessels include sclerodermatous kidney, disseminated intravascular coagulation, and malignant hypertension. Sclerodermatous kidney is organ damage caused by hardening of connective tissue, while disseminated intravascular coagulation is a condition in which blood clots form throughout the body due to overactive platelets. Malignant hypertension is extremely high blood pressure that can damage small blood vessels.

What are the tests your doctor will need?

In order to check for the criteria listed above, your doctor will order several tests. He or she will use the results of these diagnostic tests along with your symptoms to diagnose you. 

Blood tests

A complete blood count (CBC), and blood tests looking for hemoglobin and lactic acid dehydrogenase levels can check for hemolytic anemia. Lactic acid dehydrogenase is an enzyme, levels of which go up when red blood cells are breaking down.

A platelet count can reveal the presence of thrombocytopenia. 

Blood tests also can be performed to check levels of certain chemicals such as creatinine, urea nitrogen phosphorus, and potassium. They also can be used to get an estimate of your glomerular filtration rate (GFR) to look for a decrease in kidney function.

ADAMTS13 levels in your blood will indicate whether you may have TTP.

Urine tests

Doctors usually detect acute kidney injury by looking at how much urine you produce in a 24-hour period. Lower levels indicate kidney blockage and/or damage.

Your doctor also will test your urine for molecules that might indicate kidney failure.

Stool tests

Shiga or Shiga-like toxins will be present in your stools, so a stool sample analysis may be necessary.

Imaging techniques and biopsies

Your doctor can investigate the structure of your kidneys by looking for abnormalities using imaging techniques. A kidney biopsy may also be necessary and show abnormalities. 

Last updated: Dec. 15, 2020

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