Foible No. 2. Serum PSA levels may fluctuate without known reason. In one
large trial, when PSA levels were collected at yearly intervals and then later
reviewed for consistency, many men whose PSA levels appeared to be elevated---to
the point where a biopsy would normally be recommended---were found to have a
normal value when the test was repeated later. In other words, elevated PSA
levels (especially marginal elevations) may not be related to cancer, but to
unexplained fluctuations in serum levels. Foible 2 is biological variation
in serum levels.