Thrombotic microangiopathy (TMA)

by Rosemarie Tremblay-LeMay MD FRCPC
March 3, 2022

What is thrombotic microangiopathy?

Thrombotic microangiopathy (TMA) is a group of conditions where red blood cells (RBCs) are destroyed by blood clots in small blood vessels such as capillaries and arterioles. TMA is also associated with decreased platelets and organ damage.

Diseases in this group include:

  • Disseminated intravascular coagulation (DIC)
  • Thrombotic thrombocytopenic purpura (TTP)
  • Hemolytic uremic syndrome (HUS)
  • TMA occurring after bone marrow transplantation

What do red blood cells do?

Red blood cells (RBCs) are a specialized type of blood cell. RBCs are responsible for carrying oxygen from your lungs to the rest of your body and carrying carbon dioxide back to the lungs. They hold on to oxygen and carbon dioxide using a specialized protein called hemoglobin.

Normal red blood cells

Red blood cells are made in a part of the bone called the bone marrow. As young RBCs mature in the bone marrow, they produce hemoglobin. Your body needs iron in order to make hemoglobin for RBCs. Once this process is complete, the RBCs are released into the bloodstream. Normal, healthy RBCs circulate in the bloodstream for about 120 days before they are removed, and their iron is recycled to make new RBCs.

What causes thrombotic microangiopathy?

Thrombotic microangiopathy (TMA) is caused by the uncontrolled formation of small blood clots in small blood vessels. These blood clots are called thrombi. The blood clots block the inside of the blood vessel and damage or destroy the RBCs as they try to pass. Pathologists describe this process as non-immune hemolysis because the immune system is not involved in damaging the RBCs.

Conditions that can lead to the uncontrolled formation of blood clots and TMA include infections, cancer, certain types of medications, pregnancy, organ transplantation, or trauma.

Non-Immune hemolysis

How do doctors test for thrombotic microangiopathy?

Your doctor will perform blood tests to look for substances released from damaged RBCs such as indirect bilirubin and LDH. There will also be a decrease in haptoglobin. Depending on the type of TMA, tests that measure substances involved in blot clot formation may also be abnormal. There are also tests that can help determine if other organs are affected, such as the kidneys.

When a blood sample is examined under the microscope, small fragments of damaged RBCs, or schistocytes, can be seen. There will also be an increased number of immature RBCs and a decreased number of platelets.


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