The present invention relates to a method for predicting the concentration or the mass of hemoglobin or an approximation thereof, respectively, in a body fluid and/or an extracorporeal sample thereof of a patient at a later, second point of time, the patient having theoretically or in reality been administered a certain dose of an erythropoiesis stimulating agent at an earlier, first point of time. It relates further to a method for determining the dose of an erythropoiesis stimulating agent to be administered to a patient, to a method for determining whether a patient is affected by circumstances leading to the loss of hemoglobin, to corresponding devices and to an erythropoiesis stimulating medicament for use in the treatment of anemia.