Confused about post RP PSA

PSA Confusion
Rex,

The confusion flows from two different types of PSA tests. One is a newer test and considered ultra sensitive and gives you a PSA reading to three digits to the right of the decimal point. The older, standard test is a single digit.

The older test had a low limit of 0.1 ng/ml. That meant that anything below that level was "undetectable" or "zero". The new version of the test gives more digits but there are a lot of variables. Although after treatment PSA is the only real method we have of tracking the progress of prostate cancer, it remains notoriously unreliable and can be affected by many things including the time of day, OTC medications, and so forth. I frankly don't know the standard deviation for either the old or new test but of course there has to be one and I suspect that the sigma for the newer test is more than six...which could be statistically significant.

At the end of the day, none of that really matters. You have a PSA test which is below 0.1 which is a very good thing. Hopefully it will settle down and your doctor is right on about the importance of trending after treatment. A single point isn't worth much because of all the variables, but a trend can provide useful information such as doubling time, PSA velocity, and so forth which can be used as measures of success.

Hope this helps.

K

tarhoosier said:

Trendlines
Rexx:
The psa may decline a bit after surgery, for, oh, weeks, perhaps a few months. This will occasionally happen. Some men clear this psa substance slower than others as a matter of metabolism. There is also assay variation. Repeat tests may give differing values, particularly at these very low levels.
This leads to the other issue of measurement protocols. Some look only at < 0.1. Others use a more sensitive test, in order to identify trends sooner. This is unnecessary in those who are monitored after a successful intervention since 0.1 is plenty good for them. For those who may suspect a recurrence then the ultrasensitive assay such as your doctor uses may be in order. The whole point of psa is to determine a trend. Find the direction and then follow it for as long as necessary to determine when and where to make an intervention. In other words your nurse is correct.
Patience is required at this time. It is a virtue rarely found in men. We must cultivate it.

Rexx

You got good answers to your question in the posts above.
I would add that in Gleason 9 guys with a past chronology of low levels PSAs, the ultrasensitive assay (0.XX ng/ml) is proper. Also that in high risk cancers the PSA result three weeks post-op should be lower than 0.06. Some doctors use still a lower threshold to represent RP success at levels of <0.03.
According to your nurse, in your doctor’s office they use a threshold still lower at 0.015 obtained from a newer type of 3rd generation assay (0.XXX ng/ml) at their laboratory.

Surely the trend will rule the conclusion, as Tarhoosier indicates (your doctor’s approach too), but the “clean up” of PSA in the blood stream takes between 10 to 15 days to occur, which can give you an approximate answer already. The problem in readings at such low levels fall with the assays capabilities in reliable low readings. Kongo signals the need to consider assays reading tolerances too, which may influence the real final result. In ultrasensitive it can be 0.005 (which equals to 0.01).

Abbot, Siemens, Roche, Bayer, etc., assays equally have similar kits and they all present 3rd generation kits (0.XXX) used in PSA readings with limits from 20ng/ml to a lower limit of 0.005 ng/ml. They all are approved for PSA testing by NCCN, and follow the “Laboratory Medicine Practice Guidelines”, however, those lower limits varies among the kits used for the test (on average of 0.005 between kits) and, most importantly, the low variations could be an effect of the person biorhythm on the day of drawing blood.

Your next scheduled test will give you peace of mind on the matter.

Vgama