Response to letter from Dr Hoffmann

Sir, I am thankful to Dr Hoffman and Yu for their letter on our article aimed to develop simple equations for effective screening of spurious hemolysis in whole-blood specimens [1]. Several issues were raised by these authors that I will briefly comment in my reply. First, I definitely agree with the consideration that no formula can virtually distinguish between ‘spurious’ in vitro hemolysis and genuine in vivo hemolysis. However, the notion that these or other formulas may be effective to recognize also hemolytic anemia is ambitious and potentially deceptive, as the type of hemolysis that we have generated in whole-blood specimens (i.e., by mechanical aspiration of blood through a fine needle) is obviously different from that occurring in vivo as a result of a variety of human disorders [2, 3]. This concept was also highlighted by Hoffman and Yu in a following section of their letter, but incomprehensibly overlooked in this part. As such, the word ‘spurious’ cannot be removed from the title of our article, for the simple reason that this aspect is not evidence-based. The difference between the area under the curve (AUC) of the mean corpuscular hemoglobin content (MCHC) and our equation ‘hemoglobin(Hb)/hematocrit (Ht)’ can also be easily explained by the more accurate mathematical calculation enabled by our formula. In fact, our data included as many as six decimals (rounded to two for publication), whereas the MCHC is only displayed with one decimal unit by the hematological analyzers that we used in our study. It is hence conceivable that a statistical analysis using more decimal units for the MCHC value would be effective to produce a more effective discrimination between hemolyzed and nonhemolyzed samples, virtually overlapping with that of the Hb/Ht equation. The consideration about the discrepancy between MCHC and CHMC is interesting, but this information was not collected in our study for the simple reason that we aimed to identify universal equations to be applied to virtually all clinical laboratories using hematological analyzers, and not limited to those using Siemens technology. As such, this consideration is indeed not pertinent to the aim of our investigation, as clearly stated in our article. As regards the comment about the comparison between Advia 2120 and XE-2100, Hoffman and Yu discount the fact that the technology used for platelet and erythrocyte analysis was rather different (i.e., optical versus impedance), so that the changes recorded in one instrument cannot be directly translated to the other. Therefore, the assumption that the optical noise recorded by the XE-2100 may be classified as RBC ghosts or fragments in Advia 2120 is nothing but a meaningless abstraction, because no evidence can be brought in support. Conversely, our data are seemingly in favor of the opposite notion, wherein the values of RBC ghosts and fragments remained virtually unchanged after mechanical stress of whole blood, in line with data early published by our and other groups [4–6]. Finally, the fact that additional investigations should be planned to definitely establish whether or not our equations may be reliably used for screening the presence of spurious hemolysis in ‘real-world’ blood samples is indeed real, but has already been expressed in the final sentence of our manuscript. Unfortunately, Hoffman and Yu have seemingly missed to read this part of the article.