The goal

What did scientists want to find out?

People with PNHParoxysmal nocturnal hemoglobinuria (PNH)A rare disease in which the body attacks and destroys its own red blood cells, leading to fatigue, weakness, headaches and other symptoms, including chest pain and abdominal pain. who have low levels of hemolysishemolysisThe “breaking apart” of red blood cells. It can occur when the immune system attacks these cells as though they were dangerous viruses or bacteria. When red blood cells break open, hemoglobin is released. Hemolysis causes many of the symptoms of PNH. tend to experience thrombosisthrombosisThe formation of a blood clot in part of the circulatory system. Blood clots may be very serious, as they can travel to parts of the body and cause serious complications like stroke, heart attack and kidney failure., or blood clots. It’s unclear how often thrombosis occurs, and it’s difficult to identify who is most at risk.

In this retrospective analysisretrospective studyA type of study that takes data from previous studies and analyzes it. It is different from other studies that are designed and run to collect new data. In general, studies designed to collect new data are considered scientifically stronger than retrospective studies., scientists analyzed previously collected data to identify people with PNH who had low levels of hemolysis and presented with blood clots, so they could better recognize risk factors and consider how to treat the disease.

The method

How, where and when did they look for information to analyze?

With data from 429 people who had PNH, the researchers identified 25 who had clone sizesclone sizeThe percentage of red blood cells impacted by PNH. A large clone size means you have a high percentage of blood cells that can be attacked by the complement system, which may lead to more severe symptoms. over 10 percent and relatively low levels of hemolysis.

The researchers then further divided these people into 3 groups, based on the level of PNH white blood cells and PNH red blood cells.

Then, to try to reveal risk factors for blood clots, they compared people who experienced blood clots with people who did not.


The findings

What did the researchers learn?

Of the 25 people in the study, 8 had thrombosis. The individuals ranged from 21-67 years old, and the median age was 49 years.

Three of the people, or 12 percent of the group, had died. One person was in the group with thrombosis, and 2 were in the group without thrombosis.

  • Causes of death were not related to blood clots. They were dementia, metastatic cancer, and presumed complications of a bone marrow transplantBone marrow transplantation (BMT)A treatment that replaces a person’s bone marrow stem cells with cells from a donor. BMT may be a treatment option for those with PNH who do not respond to other treatments or have a significant decrease in red and white blood cells and platelets. for aplastic anemiaaplastic anemiaA rare blood disease that is a known risk factor for PNH. Aplastic anemia occurs when a person’s bone marrow does not make enough new blood cells. Some scientists believe that aplastic anemia weakens the body’s bone marrow, which then affects its ability to produce healthy red blood cells. People with PNH can share symptoms with those that have aplastic anemia, such as low blood cell counts.

The takeaway

What did the researchers conclude from the study?

  • The researchers concluded that the study’s findings make it clear that it’s important to recognize that PNH can contribute to dangerous blood clots
  • This study suggests that people with PNH who have low levels of hemolysis could still be at risk of experiencing blood clots
  • This study lends further support to the idea that factors other than hemolysis should be considered when identifying why some people with PNH develop blood clots
  • People with PNH should speak with their PNH doctors regarding the risks and benefits of medicines to prevent blood clotting
Please note: The information on this page is meant to be informational only and is not intended to replace medical advice. Always talk to your healthcare provider about any questions you may have on PNH, its symptoms or treatment.
  • Title: Letter to the editor: Significant hemolysis is not required for thrombosis in paroxysmal nocturnal hemoglobinuria
  • Journal: Haematologica 2019; 104:e94
  • Written by: Griffin, M., Hillmen, P., Munir, T., Richards, S., Arnold, L., Riley, K., & Hill, A.