I have a different perspective now being a patient myself: post-RP, Gleason 3+4=7 (only 6-10% "4" cells) with EPE, surgical margins, cribriform glands, and slight invasion of my left seminal vesicle (pT3b classification), but I was in in the clinical laboratory field for 40 years, and there is something we refer to as "clinically significant" when comparing two test results, or one result that seems to be an outlier to a group of test results on the same patient.
Generally speaking, +/- 10% difference in values is not "clinically significant." Normal, expected variation in the performance of the instrument or technologist when it's a non-automated, manual procedure, is not cause for alarm. That test could be repeated, and be back aligned closer to the previous test values, just by shear inherent method variation and test performance bias. If you had enough of one sample, you could run that specimen, say 10 or more times consecutively at the same time, and get 10 or more different values, but the difference being clinically "insignificant."
I am Diabetic. I run two tests every morning and every evening. They are NEVER the same value on my meter. One might be 110 and the other 116. The difference of 6 as a percentage of 110 would be clinically "insignificant." If one was 110 and the other was 128, that would be clinically "significant" and warranty repeat testing, and perhaps other investigations if that variability continued between each test value. That's why labs runs calibration of the instrument and control samples to ensure method and test performance stability. Each test has its normal reference range in accordance with the method and that method's accuracy (closeness to the true value) and precision (reproducibility). There are quality control method rules that every lab follows to guarantee efficacy of the test method.
"That said"...a value of 0.1 ng/ml and 0.14 ng/ml is actually a 40% difference, and therefore will likely be considered "clinically significant" by the urologist. The math is obvious: the smaller the value, the greater any seemingly "small" incremental increase might seem insignificant, but that 0.04 ng/ml increase from 0.1 to 0.14 will likely be considered clinically significant. For those wondering why the physician wants to start radiation or other therapies as soon as you hit 0.2 ng/ml, after several < 0.1 ng/ml, think about it: you might say, "but it is only 0.1 ng/ml higher than the last value", but...that 0.2 ng/ml is a "100%" increase...it doubled from 0.1 to 0.2, .since the previous measurement. Hope this helps.