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Is a hematocrit level of less than 45% important in PV?

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The Marchioli study was published at the New England Journal of Medicine in 2013 and it was a study that cemented the ideal hematocrit target of less than 45% as an attainable and desirable target for people who have PV. They took close to 400 patients and randomized them in one-to-one ratio to one of two arms, either a stringent hematocrit cutoff of less than 45% or a less stringent group with a hematocrit between 45 and 50%. This study primary endpoint looked to see for overall survival and then the existence or occurrence of cardiac events and major thrombotic events. It turned out that patients who were in the more stringent group had four times less likely chances of dying from major cardiac events or even developing major thrombotic events. I think that is the magic number that we try to strive for when treating patients who have PV.

So I think we have our answer. We really never had a large study of this size and a randomized fashion supporting the fact that less than 45% hematocrit is what you need to do when you're dealing with patients who have PV.

Even in the clinical trial I alluded to by Marchioli, there were about 25% of the patients who were randomized to the less than 45% hematocrit group and yet they never achieved that level, so I think you can expect that maybe or perhaps one out of four patients will not achieve that ideal hematocrit cutoff.

A subset of patients will not obtain the desired hematocrit, so we'll have to be on the lookout for those patients and make sure that we optimize their counts.

Image of Jamile M Shammo, MD, FASCP, FACP
Jamile M Shammo, MD, FASCP, FACP Associate Professor Rush University Medical Center | Chicago, IL
As principal investigator of clinical trials in her area of expertise, Dr Shammo is heavily involved in education, research, and administrative activities in the Division of Hematology/Oncology. She is recognized nationally for her expertise in bone marrow failure syndromes/paroxysmal nocturnal hemoglobinuria (PNH) and was chosen to serve as a national coordinator for the US PNH registry.