Hematocrit values that are even slightly out of the normal range put older patients undergoing major surgery at greater risk for heart problems and death, researchers say. Clinicians have long believed that both abnormally high hematocrit (polycythemia) and low hematocrit (anemia) contribute to surgical complications, but this is the first study to show that even mildly abnormal values are risky.

The study included 310,311 military veterans (mostly men) age 65 or older who underwent major noncardiac surgery. Blood screening occurred before surgery.

Following the patients for 30 days after surgery, the researchers found that for every percentage point outside of the normal hematocrit range (either higher or lower), the risk of death rose 1.6%. Positive or negative deviations in hematocrit levels also increased the risk of cardiac arrest and Q-wave myocardial infarction.

Researchers say further research is needed to confirm their findings and to determine if treating abnormal hematocrit levels before surgery decreases the risk of postoperative morbidity and mortality.

Source: Wu W, et al., Preoperative hematocrit levels and postoperative outcomes in older patients undergoing noncardiac surgery, JAMA, June 13, 2007.