PSA ‘<‘ value meaning

Hi hmoo,

According to my urologist most labs should be able to get down to <.01 which is considered undetectable by my doctor.  If I understand you correctly the 1st PSA reading was <.008?  If it was done by the same lab then they should be able to detect that level again on future tests.  Could this be a lab error?  Did the second test use a different lab?

Dave 3+4

hmoo,

I think you've already received your answer here, but I'll add a bit more in hopes that it might help some. I'm an analytical chemist by education, training and work experience, and in this case, the devil is in the details. When an analyst tests a blood, serum or urine sample for a particular analyte like PSA, they are essentially performing two different tests  . . . one qualitative and one quantitative. One is simply designed to determine whether the substance is in-fact present (a presumptive positive or negative), while the other, is designed to determine 'how much' of the substance is present (if any).

In that final (quantitative) stage of the analysis, the technician (or the instrument's computer software) typically compares the response of the patient sample to the response of an array of known standards (controls known to contain a certain fixed aount of the analyte). at varying concentrations. Based upon the responses of those known standards, a linear regression analysis is establlished, and two very important parameters are then determined . . .

1) Limit of Detection (LOD), and

2) Limit of Quantitation (LOQ):

The LOD (Limit of Detection) is defined as the lowest possible concentration that the instrument is capable of detecting 'qualitatively' (not quantitatively), while still being capable of distinguishing it with confidence from the background noise (the so-called signal-to-noise ratio). In other words, below the LOD, the instrument cannot tell you with confidence that the subject molecule is even PSA.

Conversely, the LOQ (Limit of Quantitation), is defined as the lowest possible concentration that the instrument is capable of detecting 'quantitatively', while still being capable of distinguishing it (within specified confidence intervals), from background noise. The LOQ is typically one full order of magnitude larger than the LOD (or more). Thus, your laboratory result of 0.064 ng/mL means that on that day, using the set of quantitative standards and quality controls available to them at the time, the instrument employed by that particular laboratory was incapable of accurately identifying and 'measuring' (or quantitating) the PSA below 0.064 ng/mL.

Given that explanation, could your PSA have actually been 0.011 or 0.008 or even 0.001 ng/mL at the time? Yes to all, because all three values are below the reported Limit of Quantitation (LOQ). Are you still likely to be "undetectable"? I'm afraid there's no accurate answer to that because "detectability" is strictly dependent on a given lab, a given instrument, a given set of standards and controls, and a given set of atmospheric conditions (i.e., signal-to-noise).

I hope that helps.

Your doctor is right. Your can't really compare 0.008 to 0.064 (your PSA results) because those data came from different instruments/labs. 

In my opinion your doctor got his own thresholds to judge outcomes. Remission after RP is considered by most when the PSA is under 0.06 ng/ml, but many take it as PSA=0.1 ng/ml. The threshold for recurrence is by tradition a PSA=0.2. Surely these thresholds may differ from patient to patient (we are different with different cases) and an increase in some particular cases could signal cancer activity but to treat due to a simple increase of the PSA may not be the best way to advance with a salvage treatment(s) because these do not assure cure if targets are not identified.

I sense you are worried for for the negative wording in your post like; " ... still undetectable ...." or " ... I’m in for a tough road ahead ...". I believe that the result of the Decipher test is making you anxious and so you may think that you are at an urgent need for additional treatment. However, the test just quantifies the risk for metastases after RP or the response of your type of cells to hormonal therapies. It does not identify recurrences or cancer's location. You must wait for such a classification given by your doctor (if ever) and you would need targets for treatment obtained via image studies. Otherwise you would follow a guessing approach based in experiences from therapies done on others.
One can try and be lucky but variations of the PSA lower than 1.0 ng/ml doesn't assure better outcomes with earlier interventions. The PSA at 0.06 is low. You have time to gather more evidences before deciding on the need of a salvage therapy and its protocol.

Hope for the best.

VG