How Is Thrombotic Thrombocytopenic Purpura Diagnosed?

Your doctor will diagnosis thrombotic thrombocytopenic purpura (TTP) based on your medical history, a physical exam, and test results.

If TTP is suspected or diagnosed, a hematologist (a doctor who specializes in blood diseases) will be involved in your care.

Medical History

Your doctor will ask about factors that may affect TTP, such as:

• Diseases or conditions you may have, such as pregnancy, cancer, HIV, infection, or lupus
• Previous medical procedures, such as a bone marrow transplant
• Medicines you take, such as ticlopidine, clopidogrel, cyclosporine A, chemotherapy, and hormone replacement therapy and estrogens

Physical Exam

Your doctor will do a physical exam and look for signs such as:

• Bruising and bleeding under your skin
• Fever
• Paleness or jaundice (a yellowish color of the skin or eyes)
• A fast heart rate
• Speech changes or changes in awareness that can range from confusion to loss of consciousness, or “passing out”
• Stroke or seizures
• Changes in urine

Diagnostic Tests

Your doctor also may order tests to help find out if you have TTP.

Complete Blood Count

This test measures the number of red and white blood cells and platelets in your blood. For this test, a small amount of blood is drawn from a vein (blood vessel), usually in your arm.

If you have TTP, your platelet count will be low and you will have a lower than normal number of red blood cells (anemia).

Blood Smear

For this test, a small amount of blood is drawn from a vein, usually in your arm. Some of your blood is put on a glass slide. A microscope is then used to look at your red blood cells. In TTP, the red blood cells are torn and broken.

Platelet Count

This test counts the number of platelets in a blood smear (see above). People with TTP have a lower than normal number of platelets in their blood. This test is used with the blood smear to help diagnose TTP.

Bilirubin Test

When red blood cells die, they release a protein called hemoglobin (HEE-muh-glow-bin) into the bloodstream. The body breaks down hemoglobin into a compound called bilirubin. High levels of bilirubin in the bloodstream cause jaundice.

For this blood test, a small amount of blood is drawn from a vein, usually in your arm. In TTP, bilirubin may be high because your body is breaking down red blood cells at a faster than normal rate.

Kidney Function Tests and Urine Tests

These tests are done to see whether your kidneys are working well. In TTP, your urine may contain protein or blood cells. Also your blood creatinine level may be high. Creatinine is a blood product that normally is removed by the kidneys.

Coombs Test

This blood test is used to see whether TTP is the cause of hemolytic anemia. For this test, a small amount of blood is drawn from a vein, usually in your arm.

In TTP, hemolytic anemia occurs when red blood cells are broken into pieces as they try to squeeze around blood clots.

When TTP is the cause of hemolytic anemia, the Coombs test is negative. It's positive when antibodies that bind to red blood cells cause your immune system to destroy the cells.

Lactate Dehydrogenase Test

This blood test measures a protein called lactate dehydrogenase (LDH). For this test, a small amount of blood is drawn from a vein, usually in your arm.

Hemolytic anemia causes red blood cells to break and release this protein into the blood. LDH also is released from tissues that are injured by blood clots as a result of TTP.

ADAMTS13 Assay

A lack of activity of the ADAMTS13 enzyme causes TTP. For this test, a small amount of blood is drawn from a vein, usually in your arm. The blood is sent to a special lab to test for the enzyme's activity.