"while expressing EtG as a ratio to creatinine is not affected by dilution. " I am also confused about this statement. I below you stated the persons drinking incident was long enough before the test to not be detected and he shouldn't have to worry about diluting. My question is what if the drinking incident was within the time frame and would drinking a lot of water help or would the EtG still show up in a dilute specimen. A lot of places that test consider a dilute test tampering and some even consider it a positive because of that. But I have been hearing lately that even if the urine was dilute - there would still be EtG in it if you had been drinking within the time frame.

First, most laboratories do not report EtG as a ratio of creatinine (U100EtG). Rather, they use the fixed value of +/-20 creatinine as a test for sample validity; under 20 is considered dilute and any reading above is considered normal.

When expressed as a ratio creatinine is assumed to be 100 and EtG is calculated as a % ratio from that value. If the actual value of creatinine is above 100 it would result in a proportional reduction of EtG reading, when below 100 it has the effect of increasing the EtG value.

These are two different approaches. One is a simple cutoff, the other a means of interpretation using 2 related values. The basis of the interpretive method is founded on the fact that urine concentration influences EtG content. More concentrate urine artificially increases the reading while a more dilute urine decreases EtG.

The U100 method is certainly simple enough to figure when the creatinine is reported quantitatively. It can be done by anyone following the test so long as both values are known (and providing the person reading the test actually understands it). Why it isn't standard practice eludes me.

Dr. Greg Skipper's website (http://etg.weebly.com/) explains the U100 method in more detail as well as providing the method for calculation. It also contains the latest update on this test.