Prostate specific antigen in urinary tract infection
Prostate specific antigen (PSA) has a reported sensitivity for prostatic adenocarcinoma of up to 80%. However, it lacks specificity. The reported positive predicted value of an elevated PSA (Hybritech Tandem-R PSA radioimmunoassay >4 ng/ml) for prostatic carcinoma in screening studies is only 28-33%. This is largely because 21-53% of men with benign prostatic enlargement (BPE) will have an elevated prostate specific antigen above 4 ng/ml. Prostatitis, including subclinical histologically proven inflammation, may lead to an elevated PSA. The physiological variation in serum PSA levels can be up to 30%. Nevertheless, serum prostate specific antigen is a useful tool in the detection and staging of organ-confined prostate cancer and the monitoring of disease progression and response to hormonal manipulation.
We present a series of 31 men (mean age = 67 years; range = 48-82 years) who were referred to the urology unit over a 17-month period with a raised PSA, BPE on digital rectal examination, and a documented urinary tract infection (UTI). Five men were asymptomatic. The mean PSA (Hybritech Tandem-R PSA radioimmunoassay) at presentation was 24 ng/ml, with a range of 5.4-100 ng/ml (normal range = 0-4 ng/ml).
A clinically significant UTI (>105 organisms per ml) was documented in all 31 patients. Following eradication of the urinary tract infection, the prostate specific antigen returned to normal (mean = 2.7 ng/ml; range = 0.3-3.9 ng/ml) in 81% of cases (25) within 17 weeks. In the remaining six cases, the PSA fell after treatment but remained persistently elevated above the normal range (9.7 ng/ml; range = 4-14.9 ng/ml). Eleven of the symptomatic cases became asymptomatic after treatment.
The failure of the prostate specific antigen to return to normal in six cases may be due to bulky benign prostate hyperplasia or an age-related variation in PSA. However, this group requires careful urological follow-up.
An uncomplicated urinary tract infection in men with benign prostatic enlargement appears to be the cause of an elevated PSA. Following eradication of the UTI, the prostate specific antigen normalizes in the majority of cases. The half-life of PSA is between 2.2 and 3.15 days. Estimation of the serum prostate specific antigen in men with benign prostatic enlargement on digital rectal examination with a suspected or documented urinary tract infection is therefore not recommended for a period of at least six weeks after successful antibiotic treatment. This will reduce the number of patients undergoing negative prostatic biopsies — a procedure not without an associated morbidity.