Hemoglobin level is an important determinant of acid-base status in hemodialysis patients

We studied the relationship between hemoglobin (Hb), which is a major buffer of blood, and arterial blood total carbon dioxide (tCO2) levels in maintenance hemodialysis (HD) patients. We also evaluated the difference between the tCO2 measured with a standard Hb value of 15 g/dl, and that assayed with an actual Hb level entered into an analyzer.

In 105 patients the predialysis tCO2 level of 21.4 +/- 2.84 mEq/l inversely correlated with the Hb level of 9.5 +/- 1.78 g/dl (r = -0.358, p = 0.0002). This indicated that the rise in Hb from 6 to 14 g/dl could result in a decrease of about 5 mEq/l in the tCO2 level. In 20 patients the tCO2 level measured at the Hb of 15 g/dl was 21.0 +/- 2.47 mEq/l, and higher (p = 0.009) than that of 20.8 +/- 2.45 mEq/l estimated at the actual Hb. The difference between these two measurements was inversely associated with the Hb level (r = -0.579, p = 0.007). The measurement of tCO2 at the unadjusted Hb slightly underestimated the degree of acidosis when the actual Hb level was < 11.5 g/dl.

The degree of anemia and, to some extent, laboratory technique should always be considered when interpreting changes in arterial blood acid-base balance in maintenance HD patients.