Altitude
Changes in levels of some of the constituents in blood
occur when measured at sea level as opposed to measurement
at a higher altitude (Table 2). For example, hematocrit
and hemoglobin levels can be up to 8% higher at an altitude
of 1,400 m.1,2 A 65% increase in C-reactive protein has been
reported at 3,600 m. Concentrations of some analytes, such
as plasma renin, serum transferrin, urinary creatinine, and
estriol, and the creatinine clearance rate decrease with
increasing altitude.