Cell Doubling Time

Panserborn

Hi all,

I've been looking in the archives to get a method of accurately measuring cell doubling time and I found posts that pointed to this website: http://www.doubling-time.com/compute.php?lang=en

Seems very useful, however, when i plug in the following data for an experiment ........
0 500000
5 640000
24 1880000
29 3000000
48 4200000
53 4320000
77 11760000
96 16640000

...... it generates a graph giving an equation of ......... "amount=946090.4145*e0.0307*time"

My problem is that when I plug the same data into excel and generate the graph there with an exponential trendline, the equation comes out as ......... y = 664510e0.0362x

Using the "doubling time = ln(2)/growth rate" formula, this results in quite a different answer.

Can anyone explain the discrepancy to me? Does the website use a different trendline calculation?

Many thanks

Gaspode

I would suspect you are right that there is a difference between the equations in Excel and the software. I've noticed this before with Excel for other equations.

Are you plotting the cell counts or getting the log of them first?

Panserborn

Just plotting numbers at the moment. Might try log .......... didn't think of that!

Gaspode

As a microbiologist I'd use Log10 rather than natural logs (e) - not sure what sort of cells you're dealing with here, but if it's bacteria then log10 is what you want.

Panserborn

They are human B-cells. Out of curiosity why would you use log10?

Gaspode

Not sure why log10 came into use but it sure makes life easy!

I came across a student handout today when searching for something else, and according to it, your figures are treated like this:

No. of Doublings in experiment = [log10(End count)-log10(Starting count)/log10(2)]
= ((Log10(16640000)-Log10(500000)/Log10(2)
= 5.056584

Growth Rate = No. Doublings/total No. of hours of experiment = 5.056584/96 = 0.0527

Doubling Time = Reciprocal of Growth Rate = 1/0.0527 = 18.99h


Not sure how that ties in with what you got already, or even if it's guaranteed to be correct, but it's one way of doing it I suppose.

Panserborn

Thanks for the info,

I'll try that equation, only issue I see with it though is that it only has a start and end data point, the expotential nature of cell growth might not play then.

Anything that makes life easier is good though

snoo

Hi all

I created www.doubling-time.com
Yes, there is a difference between the excel algorythm and the one I use for the web site.

Excel first computes a log transformation of your concentration to linearize the plot. then excel uses the least square methyd to find the equation of the regression line that fit the best. Once excel got the equation of the line, It computes the expontial form of the line equation.

but this method of calculation gives greater weights to small concentration values. And there is no experimental reason to do this.

So I use a different algorythm that processes an exponential fitting without using the linearization step. this method is described on mathword. This method makes the weights identical for low or high concentrations.

hope it helps.

Gaspode

Thanks Snoo.
90% of the math there goes over my head, but that's a good reference to fall back to if need be!