10 replies to this topic

[Johnc]

Does anyone know how this is calculated or is this a special test? The Inc talked about a 3 or 4 log reduction. How can I calculate that number

I would greatly appreciate some help her.

Thanks in Advance,

Johnc

[scuba]

John -

If you have a hundred of something (100) and reduce it to ten of something (10) - you have a one (1) log reduction. If you continue and reduce the 10 of something to 1 you have a two log reduction (from the original 100) and if you reduce the 1 of something to 0.1 you have a three log reduction (again from the original 100). Another way to thing of "log" is that every time you move the decimal place from right to left one spot you have a one log reduction. If you move the decimal place one spot to the right, you have a one log increase:

100.0 (start) (log = 2)

10.0 (one log reduction) (log = 1)

1.0 (two log reduction) (log = 0)

0.10 (three log reduction) (log = -1)

So ... Log (100) - Log (0.1) = 3  (that's where the 3 log reduction phrase comes from)

Take your calculator and enter 100. Then press the "log" function and note the result in the display. It will read 2 ... write that down. Now enter in your calculator the number 0.1 and press the log button. The display will read -1.0 ... write that down.

Now calculate the difference between 2 and -1 ....   2 - (-1) = 3 .....that's the 3 log reduction.

So - with that in mind, if someone starts with a PCR of 100% and their PCR drops to 10%, they have a one log reduction. What the Oncologists like to see is a three log reduction from whatever your original base point is. So, again, if you are starting at PCR = 100%, then a three log reduction would be 0.1% (just move the decimal three places to the left). Oncologists define a 3 log reduction as a Major Molecular Response where statistics show that the odds of CML progression are very low. It does matter how long it takes to get to a three log reduction, but that can depend on many other factors.

If your starting PCR = 150%, then a three log reduction from that level = 0.15%. (Never appreciated how one could have more than 100% of something, but they're doctors and like to complicate things).

For all practical purposes, when a PCR level drops to 0.1% - a patient is said to be in MMR which is essentially a 3 log reduction from the typical starting points seen.

A PCR that is equal to 0.01% is a 4 log reduction. A 4 log reduction is a nice place to be. Some people get to 0.001% (basic limit of PCR) and although that could be called a 5 log reduction, it really is at the limit of the technology and in the noise. Anything below 0.01% is excellent. Even 0.1% is very good.

So if you want to know what your log reduction level is - all you do is take the log of the starting value and then take the log of the second value and then subtract the two numbers:  Log(100) - log(0.1) = 3

And using PhilB's rabbits - if you have a Million rabbits and a lot of them die so you end up with only 1,000 rabbits - you experienced a 3 log reduction. That's a lot of rabbits.

[Trey]

http://community.lls.org/docs/DOC-1273

[PhilB]

scuba wrote:
Take your calculator and enter 100. Then press the "log" function and note the result in the display. It will read 2 ... write that down. Now enter in your calculator the number 0.1 and press the log button. The display will read -1.0 ... write that down.
Now calculate the difference between 2 and -1 ....   2 - (-1) = 3 .....that's the 3 log reduction.

Wow, it's years since I've come across anyone with a scientific calculator with a log button on it!  Serious nostalgia.

For those using MS Excel instead, the formula is just =LOG10 (New figure / Old figure).  Using Scuba's example that would give the answer -3 ie a 3 log reduction.

[Johnc]

Scuba, PhilB and Trey

This is exactly what I was looking for.

Thank You very Much!

Have a great weekend

Johnc

[scuba]

PhilB - You mean to tell me you don't have one of these. Come on ... surely everyone has an HP32SII

[pammartin]

Is that a calculator, computer, or device to destruct on command?  I got lost on the 2nd row of buttons

[pamsouth]

Looks like we have a few on this board who really know their number.

PamSouth

[LivingWellWithCML]

Ha - love the picture Michael.  I still use the same HP28S that I bought in college back in 1987.  I can't believe the darn thing still works, but I love it.  It's sitting on my desk right now, ready to calculate PCR log reductions ad nausem.

[Trey]

Michael's Measuring Process:

1) Measure with a micrometer

2) Cut the measurement with a meat-axe

3) Take the inverse  of pi times the absolute number from 2 above

4) Sprinkle some b2m on it

5) Allow to come to room temperature

6) Serves six

[cousineg]

More information about   Polymerase Chain Reaction (PCR) - CML

P.S. If you've just been diagnosed , I suggest you to meet Carolyn Blasdel .