Falling Hematocrit Value on Cessation of Smoking

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Abstract
To the Editor.— A falling hematocrit value three or four days after the admission of a critically ill patient to the hospital is a cause of great concern. Several possible causes must be considered. Bleeding into a surgical site or area of previous trauma, stress gastrointestinal bleeding, infection, hydration, disseminated intravascular coagulation, hemolysis, thrombocytopenia secondary to medication, or even excessive phlebotomy done to follow laboratory values in these complex patients are all at one time or another implicated as the cause of falling hematocrit values. An additional factor that has not received attention but that perhaps should in this particular group of patients is alterations in plasma volume secondary to the abrupt discontinuation of smoking in heavy smokers. Rapid changes in hematocrit values occurring over several days have been noted with the sudden cessation (decreased value) or resumption (increased value) of smoking,1and it has even been recommended that the fall in hematocrit value after discontinuation of smoking be used as a screening test to distinguish polycythemia caused by smoking from polycythemia vera.2 Several mechanisms have been postulated to explain the changes observed. These include abnormalities

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