In patients with a normal digital rectal examination and serum PSA lev
els under 18.4 ng/ml Yang (i.e. under 10.0 ng/ml Hybritech or under 14
.4 ng.ml with the Basel Cantonal Hospital assay), twice yearly then ye
arly follow-up examinations are sufficient. More closely spaced examin
ations and a transrectal ultrasound scan are appropriate in patients w
ith abnormalities upon digital rectal examination, especially when ser
um PSA levels are consistently elevated.