Here’s an excellent question that comes up from time to time in class. It has to do with units of measurement, which sounds like a boring and unimportant topic – but it can be very confusing if you’re not aware of the different systems people use.
Q. I have a very odd question about cell counts. I’m looking over my notes and saw where my Professor listed a high white count as 60000 (6.0 x 109)/L. I don’t understand what she means by 6.0 x 109/L because if that were the case the white count would be 6,000,000,000. I tried looking it up but often times I see white counts listed as 109. Shouldn’t it be 106?
A. I know what you’re saying – it is confusing! There are three ways the white blood cell count can be listed:
- number of cells per μm
- number of cells per mm3
- number of cells per L
The first two units are more commonly used in the US. The third is part of the metric system, and is used more commonly in other countries. This system is also called the International System of Units, and is usually referred to by the abbreviation “SI.” Which didn’t bug me until I wrote this post, and then I was like, wait, SI?? Turns out the abbreviation comes from the original French name, Système international d’unités. In case you were wondering.
Here are typical reference ranges for the two systems:
- Conventional: 4,000 – 11,000/μm or 4,000 – 11,000/mm3
- SI: 4.0 – 11.0 x 109/L
The confusion arises when people are talking (or sometimes even writing) about the white count. Nobody says the patient’s white count is “8,200/mm3” – they just say “8,200.” So if you don’t have the context of their comment, you don’t know if that means that the patient’s white count is normal (8,200/mm3), or very high (8,200 x 109/L).
Usually, it’s fairly obvious in real life. A WBC count of 8,200 x 109/L , for example, would be incompatible with life. Sometimes, though (especially on exams, where trick questions are unfortunately pretty common), you really need to know the units. If it’s not abundantly obvious which units are implied, then you need to ask!
Back to your question. The confusion arose because the units were not listed correctly. It would be correct to say that 60,000/mm3 is a high white count. This number would be equivalent to 60.0 x 109/L in the SI system. The other number you listed – 6.0 x 109/L – is within the normal range. And you’re right: 60,000 x 109/L would be a ridiculously high white count (one that would not be seen in humans!).
Whew, very informative. There are things you take for granted and then suddenly you discover you know nothing about it.
never thought of such things!!! so basic yet very intriguing!!
thank u so much doctor!!!
very nice subgect.
In the case of platelets. read the book platelet counts between 150 and 10 450.000 X 10 9 / L.ETA this correct?
The normal range for platelets is about 150 – 450 x 10^9/L
hi…in very few days i have become a great fan of this site..m pursuing my post graduation in pathology its so much fun learning all this so effostlessly….
Thanks, Ankita! So glad you like the site! 🙂
I agree – this is an excellent website. I just wanted to make one more comment on this in regards to white blood cell counts in donated blood products. For instance for transfused platelet collections, there are regulatory restrictions on the number of white cells allowed in the product. In this case, the white cell count is measured in 10E6 cells/dose . The max limit in the US per FDA is 5.0 X 10E6 and in the EU it is less than 1.0 X 10E6.
Thank you so much for the excellent clarification. This is extremely helpful information. Keep up the terrific work!
Is there anyone who knows how to covert % reference ranges to 10E 9/L for Differentials (ie. Neutrophils, Lymphocytes, Monocytes, etc)?
Sure – you just multiply the percentages by the total white blood cell count. For example: the normal white blood cell count is 4.5 – 11 x 109/L. The normal percentage of neutrophils is 45-75%. So the normal lower end of the absolute neutrophil count is about 2 x 109/L (4.5 x .45), and the normal upper end of the absolute neutrophil count is about 8 (11 x .75).
STILL I DONT UNDERSTAND-LOWER NORMAL RANGE IS 4.0 x 103/μL THAT MEANS IN 1uL THERE ARE 4000 CELLS,SO BY CALCULATION IN 1 LIT I.E 1000ul there should be 4000*1000=4*10 6 cells/L WHY IS IT WRITTEN 4*109/L
There are a million microliters in a liter (1 L = 1,000,000 microliters). So 4,000 cells/microliter = 4,000,000,000 cells/liter.
very informative
Just for clarification, how to get percentage from absolute count? ….you have given an example how to get the absolute count from percentage”multiply the percentages by the total white blood cell count. For example: the normal white blood cell count is 4.5 – 11 x 109/L. The normal percentage of neutrophils is 45-75%. So the normal lower end of the absolute neutrophil count is about 2 x 109/L (4.5 x .45), and the normal upper end of the absolute neutrophil count is about 8 (11 x .75).
What does the ^ mean in the RBC of 4.16 10^6/ul?
The ^ is shorthand for “superscript” and it applies to the 6. So 10^6 means 106
Thank you Christine