Log Reduction Calculation Help: The Leukemia & Lymphoma Society Community

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2 Replies Last post: Nov 13, 2009 2:23 AM by PhilB

Sneezy12

72 posts since
Apr 21, 2009

Currently Being Moderated

Nov 12, 2009 4:53 PM

Log Reduction Calculation Help

My April 28-09 bcr/abl value at diagnosis was 19.81% Raw value, ( NOT the Int. Scale ). My 11-02-09 value was 0.08% Raw value ( Equal to 0.2% on the Int. Scale ). Can someone please tell me the Log Reduction and how to calculate it. Thank you. Frank

Trey

603 posts since
Mar 27, 2009

Currently Being Moderated

1. Nov 12, 2009 8:59 PM

in response to: Sneezy12

Re: Log Reduction Calculation Help

Using your diagnosis PCR, your personal starting point would be 19.81%. Let's just round that off to 20% since it is so close. Then your log reductions would be as follows:

Baseline: 20%

-1 log: 2%

-2 log .2%

-3 log: .02%

So your current .08% is between -2 log and -3 log, and is 2/3 closer to -3 log; so approx -2.7 log reduction.

This also assumes the same lab did both PCRs.

http://www.ciriscience.org/a_107-What_is_Log_Reduction

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PhilB

236 posts since
Apr 7, 2009

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2. Nov 13, 2009 2:23 AM

in response to: Trey

Re: Log Reduction Calculation Help

Sorry Sneezy, what you have is actually a 2.4 log reduction rather than 2.7. If you have excel then the easiest way is to first work out your reduction as a fraction:

0.08 / 19.81 = 0.004038

Then calculate the log of the result using the formula:

=log10(0.004038)

which gives the result -2.3979. The '-' indicates that it's a reduction.

Afraid that Trey made the classic error of doing a linear interpolation on a logarithmic scale - even Homer nods!

Phil

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Nov 12, 2009 4:53 PM

Log Reduction Calculation Help

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