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Hemoglobin (Hgb) and hematocrit (Hct) are often used interchangeably to evaluate anemia in dialysis patients. Hgb is the preferred method in most European countries, while Hct is generally used by clinicians in the United States. This article examines the comparative accuracy of these two values, including a same-patient assessment of laboratory samples. These data illustrate that Hgb is a more accurate method of assessing anemia. Using Hgb may help nurses and patients by: (a) decreasing variability in laboratory assessment, (b) avoiding ongoing errors in anemia measurement, (c) decreasing the nursing time spent on anemia management, and (d) increasing the potential for patients remaining in the recommended DOQI target Hgb range of 11 g/dL to 12 g/dL.
Hemoglobin (Hgb) and hematocrit (Hct) continue to be the hallmark laboratory parameters used to monitor and manage anemia in dialysis patients. Nephrology clinicians generally assume that these two tests are equally useful and therefore use them interchangeably. This practice has been perpetuated by the seemingly close correlation between Hgb and Hct, and the clinical practice of multiplying the Hgb times three to calculate an approximate Hct level (Hillman & Finch, 1994).
Despite the frequency of this practice, clinical evidence indicates that Hct readings are more likely to be affected by outside influences, with the ensuing potential for variability in serial readings. This article examines the comparative accuracy of Hct and Hgb, including a retrospective analysis of samepatient laboratory data. Potential implications for clinicians who care for anemic dialysis patients are explored as well.
Laboratory Measurement of Hgb and Hct
Hgb, a blood-borne protein that facilitates the transport of oxygen to, and the removal of carbon dioxide from tissue, constitutes over 90% of a normal red blood cell (each cell contains almost 250 million Hgb molecules). Hgb is composed of two pairs of globin chains and four heme groups containing ferrous iron. It is commonly measured by automated spectrophotometry in which the red cell is lysed and the total Hgb count is determined by measuring the iron-containing pigment. Hgb thus provides a direct measurement of the oxygen carrying capacity of the blood (McClatchey, 1994).
By contrast, Hct provides an indirect measurement of the body's oxygen-carrying ability. Hct can be determined either by automated blood-counters or by microhematocrit (or spun)...