hemoglobin

The researchers tracked participants' blood pressure, a marker for blood clot and stroke risk; measured hemoglobin levels to check whether the pumps were breaking red blood cells; and monitored patients for other complications.

Part of this is due to changes in the regulation of the EPAS1 gene, which lowers hemoglobin concentrations by regulating the pathway that responds to changing oxygen levels.

"Tibetans have, in general, an average lower hemoglobin concentration, and their physiology deals with low oxygen in a way that doesn't increase their red blood cells to excessively high levels. Now we have the first signs of evidence that Andeans are also going down that path, involving the same gene, but with a protein-coding change. Evolution has worked in these two populations, on the same gene, but in different ways," said Simonson.

This results from either lower than normal levels of red blood cells or a decrease in the quantity or quality of hemoglobin, the protein that allows these cells to transport oxygen.

Low values of red blood cell count, or RBC, hemoglobin, or Hb, and hematocrit, or HCT, would indicate that the patient is suffering from anemia.