From creatine kinase-MB to troponin: do we really need to differentiate between myocardial injury and infarction?

To the Editor: We read with interest the article by Fernandez et al. Reticulocyte hemoglobin content (CHr) is a promising marker of iron metabolism, particularly in the intensive care unit setting where usual markers are often disrupted by inflammation. In a small cohort of critically ill patients with no evidence of real iron deficiency, we observed a correlation between C-reactive protein and CHr, suggesting that inflammation rapidly reduces iron availability for erythropoiesis. We agree that CHr should be used in future research protocols to monitor the response to iron therapy in critically ill patients. However, CHr measurements are not routinely available in most hospitals. In our study, blood samples had to be stored on ice and sent to an external laboratory within 72 h. In the study by Fernandez et al., it would have been interesting to know the iron status of the patients based on the ferritin concentration, serum iron concentration, and transferrin saturation to ensure that there was no coexistence of true iron deficiency. Also, because CHr is the product of cellular volume and cellular hemoglobin concentration, other variables such as mean cellular volume may have affected the CHr values. In our study, two patients had a high CHr value ( 35 pg) probably secondary to their high mean cellular volume values (more than 100 fl). CHr seems to be useful to predict transfusions or to monitor iron therapy but should be interpreted in the context of folates or vitamin B12 deficiencies that may coexist in critically ill patients.