Medical Archive

C59 Anemia and Polycythemia

Hematopoiesis and the physiologic basis of red cell production

FIGURE 59-1
The physiologic regulation of red cell production by tissue oxygen tension.

FIGURE 59-2
Erythropoietin (EPO) levels in response to anemia. When the hemoglobin level falls to 120 g/L (12 g/dL), plasma EPO levels increase logarithmically. In the presence of chronic kidney disease or chronic inflammation, EPO levels are typically lower than expected for the degree of anemia. As individuals age, the level of EPO needed to sustain normal hemoglobin levels appears to increase.

Anemia

Clinical presentation of anemia

Approach to the patient

Laboratory evaluation

Peripheral blood smear

Reticulocyte count

Corrected reticulocyte count (%)
- = reticulocyte (%) * [??? Hct / ?? Hct (45%)]
Reticulocyte production index (RPI)
- = corrected reticulocyte count / shift correction factor
- RPI >2.5 – ??, ??, hemoglobinopathy
- RPI <2.5 – hypoproliferation (eg., aplastic anemia), maturation defect (eg., IDA)

FIGURE 59-13
Correction of the reticulocyte count. To use the reticulocyte count as an indicator of effective red cell production, the reticulocyte number must be corrected based on the level of anemia and the circulating life span of the reticulocytes. Erythroid cells take ?4.5 days to mature. At a normal hemoglobin, reticulocytes are released to the circulation with ?1 day lex as reticulocytes. However, with different levels of anemia, reticulocytes (and even earlier erythroid cells) may be released from the marrow prematurely. Most patients come to clinical attention with hematocrits in the mid-20s, and thus a correction factor of 2 is commonly used because the observed reticulocytes will live for 2 days in the circulation before losing their RNA.