Thread: Hemoglobin relationship to Hematocrit?

Is there a formula for converting Hematocrit count to Hemaglobin count or the reverse?

Hemoglobin and Hematocrit are two different things. But typically the Hematocrit is approximately 3 times the Hemoglobin.

The hematocrit is the proportion, by volume, of the blood that consists of red blood cells. The hematocrit (hct) is expressed as a percentage. For example, a hematocrit of 25% means that there are 25 milliliters of red blood cells in 100 milliliters of blood.

The hematocrit is typically measured from a blood sample by an automated machine that makes several other measurements at the same time. Most of these machines in fact do not directly measure the hematocrit, but instead calculate it based on the determination of the amount of hemoglobin and the average volume of the red blood cells. The hematocrit can also be determined by a manual method using a centrifuge. When a tube of blood is centrifuged, the red cells will be packed into the bottom of the tube. The proportion of red cells to the total blood volume can be visually measured

In normal conditions, there is a linear relationship between hematocrit and the concentration of hemoglobin (ctHb). The relationship can be expressed as follows:

Hct (%)= (0.0485 x ctHb (mmol/L) + 0.0083 x 100

A low hematocrit reflects a low number of circulating red blood cells and is an indicator of a decrease in the oxygen-carrying capacity or of overhydration. A high hematocrit may reflect an absolute increase in the number of erythrocytes, or a decrease in plasma volume.

You'll find a useful graphic on this here: [media]http://www.transfusionguidelines.org.uk/lcs/graphics/normalxbloodxcount.xcalculations.gif[/media]

Lawrence, what graphic are you referring to? Got a link?

[media]http://www.transfusionguidelines.org.uk/lcs/graphics/normalxbloodxcount.xcalculations.gif[/media]

Link from Laurence

In normal conditions, there is a linear relationship between hematocrit and the concentration of hemoglobin (ctHb). The relationship can be expressed as follows:

Hct (%)= (0.0485 x ctHb (mmol/L) + 0.0083 x 100

shouldn't this be

Hct(%)=((0.0485 x ctHb (mmol/L) + 0.0083) x 100

otherwise the multiplication of 0.0083 would occur first,

why do you use mmol/L when Hb is measured as g/dL

mmol/L=g/dL

1L=10dL
mmol/10dL=g/dL
therefore mmol/10=g

does this work out? How many grams of haemoglobin equates to one mole [what is the formula mass of haemoglobin]

Good catch on that typo mistake! You are correct on your placement of the brackets. I had checked a reference when giving my initial answer that was from author in Denmark, accounting for the difference in giving measurements in mmol/L instead of g/dL, which is what is used in the U.S. After re-checking the site, I thought the following additional info might be of interest.


As there is a linear relationship between hemoglobin (ctHb) and hematocrit, it is possible to calculate the hematocrit on analyzers that measure hemoglobin. When making this conversion, two factors should be taken into consideration:

• The analytical quality of the ctHb measurement
• The precision of the equation that converts the two parameters

The measurement of ctHb from most good-quality analyzers is usually reliable; however, the equations used to calculate the hematocrit vary from analyzer to analyzer. Some analyzers use an empirically found equation, whereas others use an approximate conversion factor of 3.
Example:

Hb concentration
15*Hct (%) = (0.0485 × ctHb (mmol/L) + 0.0083) × 100 result is Hct of 45.98
15 Hct (%) = 2.8 × ctHb (g/dL) + 0.8 result is Hct of 42.80
15 Hct (%) = ctHb (g/dL) / 0.34 result is Hct of 44.12
15 Hct (%) = 2.941 × ctHb (g/dL) result is Hct of 44.12

* Conversion factor: g/dL × 0.62058 = mmol/L


Notice that all of the results for the same Hgb level are not identical. The conclusion to all of this is, that while it is generally assumed that the conversion from hemoglobin to hematocrit is pretty straightforward, since most methods measuring ctHb are considered to be fairly accurate, when looking at Hct levels, the healthcare professional needs to remember that different analyzers use different conversion factors, which may compromise the reliability of the hematocrit result.

If you would like to review the entire article, it can be found at the following site:
Hematocrit

the output I take it is the haematocrit, is there any machines which measure directly the haemoglobin?

I take it the specific equation used would be in the manual, I'll need to look through those 4 equations in more detail to see what each refers to

thanks

There is a new technology that we have been trialing here at CUMC that acts as a pulse-ox and gives us a noninvasive and continuous Hb measurement which is beneficial when dealing with acute and chronic anemia patients. The machines are expensive, but if you have the right kind of RT monitors, the technology can be added at quite a reduction in cost. We have one on our pediatric unit, and one being tried in cardiovascular surgery, looking forward to seeing how they measure up. This would be especially helpful for patients who are critically anemic and cannot afford to lose even a drop of blood. If you want specifics, send me an e-mail.