A New Mechanism for Controlling the Number of Red Cells in the Blood

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The summary below is from the full report titled "Neocytolysis on Descent from Altitude: A Newly Recognized Mechanism for the Control of Red Cell Mass." It is in the 17 April 2001 issue of Annals of Internal Medicine (volume 134, pages 652-656). The authors are L Rice, W Ruiz, T Driscoll, CE Whitley, R Tapia, DL Hachey, GF Gonzales, and CP Alfrey.

What is the problem and what is known about it so far?

Red blood cells, which transport oxygen to the tissues, grow from immature cells in the bone marrow and are released into the bloodstream when they reach maturity. This maturation process is controlled by a hormone known as erythropoietin, the level of which is controlled by the amount of oxygen in the blood. After reaching the bloodstream, red cells usually survive for about 120 days before being destroyed. Astronauts, when they return from space, have been found to be anemic (too few red cells) as a result of red cell destruction. During space travel, however, instead of destroying the oldest red cells as it usually does, the body selectively destroys the youngest red cells, a process called "neocytolysis."

Why did the researchers do this particular study?

To find out if neocytolysis occurs in circumstances other than space travel, such as when people who live at high altitude descend to sea level. They also wanted to know if erythropoietin levels in the bloodstream are related to neocytolysis.

Who was studied?

Nine healthy, nonsmoking men, aged 26 to 53 years, living in Cerro de Pasco, Peru (4380 meters, or about 13,000 feet, above sea level), were studied. All participants had extra red cells because of the lower levels of oxygen at high altitude.

How was the study done?

Initial blood studies were done while the participants were living at high altitude. All participants then descended to sea level. Three participants were given daily injections of erythropoietin, beginning on the day of descent. At sea level, special blood tests were done to determine whether red cells had been destroyed and whether the destroyed cells were young or old. The amount of erythropoietin in the bloodstream was also measured.

What did the researchers find?

In participants not receiving erythropoietin, the number of red cells decreased by 7% in 3 to 7 days; erythropoietin levels also decreased dramatically on descent to sea level. Blood test results in these participants showed that young red cells had been selectively destroyed. No evidence of red cell destruction was found in men receiving erythropoietin.

What were the limitations of the study?

Before the study began, two participants had visited towns at sea level, briefly getting more oxygen on each trip; this could have affected erythropoietin levels in these participants. Also, chemical labeling of young versus old red cells was not conclusive for technical reasons. Finally, the results may not apply to all persons, since only a few participants were studied and no women were included.

What are the implications of the study?

Rapid destruction of young red blood cells (neocytolysis) occurs in circumstances other than space travel, probably because of a decrease in erythropoietin level. Better understanding of the effects of changes in erythropoietin levels may lead to its more efficient use in patients, including those receiving kidney dialysis.