The goal

What did scientists want to find out?

For doctors who treat individuals with PNH, it’s important to detect PNH cells and measure PNH clone sizeclone 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. .

Usually, doctors determine clone size via flow cytometryflow cytometryThe most common method of testing for PNH, this test confirms whether red blood cells are missing their protective shield. It also calculates the percentage of blood cells impacted by PNH, which is referred to as your clone size. 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., which is done on samples of peripheral blood. Peripheral blood simply means the blood that circulates freely throughout the body.

However, in this article, researchers reviewed and recapped studies (this is often called a 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.) showing that carefully analyzing bone marrowbone marrowThe soft fatty tissue inside certain bones that houses stem cells, some of which will ultimately become blood cells. Bone marrow provides the nutrients and environment needed for blood cells to be created. Once these cells are fully mature and ready to go to work, they leave the bone marrow and enter the bloodstream. samples can detect PNH about as well as using blood samples.

The method

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

Doctors detect PNH cells and measure PNH clone size by testing blood cells for GPI-anchored proteins. These proteins help protect blood cells from hemolysis. Determining whether GPI-anchored proteins are absent can help diagnose PNH.

To do this, doctors use FLAER, short for Fluorescein-labelled proaerolysin, a harmless molecule created in a lab. FLAER molecules bind to GPI anchors, so using FLAER provides a direct measurement of GPI anchors.

Testing using peripheral blood

Since the 1990s, doctors have tested peripheral blood using flow cytometryflow cytometryThe most common method of testing for PNH, this test confirms whether red blood cells are missing their protective shield. It also calculates the percentage of blood cells impacted by PNH, which is referred to as your clone size. 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.. They conduct these tests both to detect PNH or other blood disorders, and to measure PNH clone size.

Why peripheral blood? GPI anchors are produced more consistently by cells in peripheral blood. This makes them easier to detect.

However, testing peripheral blood may lead doctors to underestimate a patient’s PNH clone size because:

  • 1

    The immune system might attack and destroy PNH red blood cells before they can be measured

  • 2

    People with PNH often receive transfusions of normal red blood cells to improve anemia symptoms. These additional cells can throw off measurement of the body’s own red blood cells

Flow cytometry is more sensitive—or less likely to produce a false negative—when used with red blood cells than with white blood cells. But white blood cell counts may better reflect clone size, because:

  • 1

    The immune system spares white blood cells from attack

  • 2

    Transfusions of red blood cells do not affect the body’s own white blood cell count

Testing using bone marrow

Doctors have never studied how useful it also might be to use samples of bone marrow to detect PNH and measure clone size.

Bone marrow aspiration is a procedure where doctors take a sample of your bone marrow through a needle. It is more invasive than a peripheral blood draw. This is often performed in patients with cytopenia, which means there are not enough mature blood cells in the bloodstream.

Based on review of previously completed studies (a 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.), testing stem cells in bone marrow has shown promise:

  • One study found a high correlation of PNH clone size in a side-by-side analysis of peripheral blood and bone marrow

  • Scientists also determined that PNH red blood cells mostly can be identified in bone marrow

Researchers showed that FLAER binds to all normal white cells in bone marrow, which allows PNH white blood cells to be more easily identified.

FLAER can help doctors identify the PNH clone in all bone marrow stem cells in a single test.

Doctors also use monoclonal antibodies, which are molecules made in a lab, designed to mimic the immune system by binding to other specific molecules. For these tests, the monoclonal antibodies are designed to bind to GPI-anchored proteins.

Monoclonal antibodies can help show which red blood cells were created by which stem cells in the bone marrow. This is called a stem cell lineage.

Researchers also tested 2 types of white blood cells from bone marrow, both in people with PNH and in healthy volunteers.

They found very few false-positive or false-negative PNH cases when they analyzed a single stem cell lineage.

When they analyzed both lineages together, PNH detection was 100 percent accurate.


The takeaway

What did the researchers conclude from the study?

  • Peripheral blood is still the preferred choice to test for PNH. But the researchers concluded that the studies they reviewed show that properly analyzing bone marrow can help detect and measure PNH equally well—and it might even be more accurate in determining clone size
  • Collecting blood samples from people with cytopenia is often challenging. For these people, the option to test for PNH cells using bone marrow may be valuable
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: Detection of paroxysmal nocturnal hemoglobinuria (PNH) in bone marrow aspirates
  • Journal: Seminars in Hematology 56 (2019) 65–68
  • Written by: Dulau-Florea, A., Maric, I., Calvo, K. R., & Braylan, R. C.