Hemoglobin is NOT Different from Hematocrit… Once and for All!

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It starts in medical school, regularly appears in your medical training, sneaks around nursing schools and is an impetus for discussions in the ICU: The great myths about Hemoglobin (Hb) and Hematocrit (Hct).

These two haematological lab-parameters are part of our daily life at work and are mostly measured together… as a package. Some clinicians look at haemoglobin levels, others prefer hematocrits levels… but then there is always someone making a great deal of differentiating between the two parameters and making all sort of diagnostic conclusions. ‘Hct is better to determine dilution of the patient’ or ‘Acute blood loss is better determined by Hb than Hct’… and so on.

So here’s the question: What actually is the difference between Hb and Hct? Do we need to measure both in clinical practice?
What’s the difference?

Hemoglobin levels are mostly measured by automated machines designed to perform different tests in blood. Within the machine, the red blood cells are broken down to get the haemoglobin into a solution. The concentration of haemoglobin is then measured by spectrophotometry using the methemoglobin cyanide method.

Hematocrit levels in contrast are actually calculated by an automated analyzer… It is actually not measured directly! The analyser multiplies the red blood cell count by their mean corpuscular volume.
What is Fact?

There is NO difference between Hemoglobin and Hematocrits by means of clinical information!
In fact, virtually all haemoglobin in our blood is contained within erythrocytes
Therefore, whether the amount of Hb per litre of blood is determined or the blood’s volume occupied by the Hb filled erythrocytes is determined, similar information is gained.
Nijboer at al. have brilliantly proven that Hb and Hct correlate in all ranges and all patients and also nicely show this in their figure 1 (see below)
The only rare exceptions are macrocytic and polycystic anaemia in which the Hct is defined by erythrocytes containing a normal mean corpuscular Hb concentration

Conclusion
Hemoglobin is NOT different from Hematocrit

Both parameters provided identical clinical information
Once and for all!
Both parameters provided identical clinical information
Once and for all!

JTrauma

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