If Anemia was a coin, then I fancy Hemoglobin (HgB) and Hematocrit (HcT) would be the two sides of this coin – or are they ? In a patient with established or suspected bleeding, it’s common practice to ‘trend’ anemia progress by ordering an “H & H” or HgB & HcT every 6-8 hours. Most of you probably know that Hematocrit tends to be thrice or three times Hemoglobin. (Yes thrice is a real word 😆) . It got me thinking – Do we really need to check both ? Which one is better ?
In most labs using automated / electric cell counters, Hemoglobin concentration is a direct measurement while Hematocrit value is a derived measurement using Red Blood Cell (RBC) counts and Mean Corpuscular Volume (MCV). HcT can also be directly measured , usually in places without electronic counters and in medical schools hematology class, using a visual method off a centrifuge to see how much of blood volume is compacted red cells. You can see right off the bat how Hematocrit can be subject to variations and possible errors.
A retrospective cross-sectional study published in 2020 found that HgB was more reliable and consistent measure of anemia while HcT levels were variable in the same person with poor specificity. A study published in 2017 evaluated accuracy of Point of Care Testing (POCT) devices that measure quick labs using blood in a ABG sampler comapared to standard clinical lab machines. It showed showed most labs were underestimated but Hematocrit levels were even more way off when compared to Hemoglobin – the study specficially stated that the “mean bias for Hb, K and Na in the present study is within USCLIA (US Clinical Laboratory Improvement Amendment) accepted differences but not for Hematocrit.”
Hemodilution errors will affect both HgB and HcT. So does one really need to check both ? Some clinical food for your thought ! Cost-wise I doubt there is any difference to check Hemoglobin alone or in combination with Hematocrit. But in term of time-to-result and blood volume needed to test – I am not sure if a real difference and can be checked with individual labs.
P.S: I have explained earlier why with an acute bleed, immediate hemoglobin check might be normal yet and needs time to lower.
