Absolute reticulocyte count is a percentage, not a count. It’s just the straight-up percentage of red cells that are reticulocytes (normal is about 0.5 – 2.0%). That’s useful as it is. However, it doesn’t reflect that fact that as the hemoglobin drops, you should have more reticulocytes, percentage-wise (in other words, at a hemoglobin of 50 g/L, you should have a much higher percentage of reticulocytes than you should at a hemoglobin of 100 g/L). To take this into account, you can do a corrected retic count.
Corrected reticulocyte count is reticulocyte % x (Hgb/15). This formula “corrects” for hemoglobin – meaning that it will show you if the patient is making enough reticulocytes for the degree of anemia present. As the hemoglobin drops, you need to make more reticulocytes to get up to the normal range of 0.5 – 2.0%.
Absolute vs. corrected reticulocyte count