Falsely Undetectable Prostate-Specific Antigen (PSA) Due to Presence of an Inhibitory Serum Factor: A Case Report and Review of Pertinent Literature

Patient: Male, 63

Final Diagnosis: Recurrent prostate cancer

Symptoms: Falsely undetectable PSA

Medication: —

Clinical Procedure: Serum dilution

Specialty: Urology

Proximity Ligation Real-Time PCR: A protein-based confirmatory method for the identification of semen and sperm cells from sexual assault evidence

The positive identification of seminal fluids in sexual assault crimes is considered crucial evidence to determine whether a sexual act occurred or not. However, current presumptive methods lack specificity and sensitivity. Confirmation of semen by microscopic examination of spermatozoa is laborious, time consuming, and can sometimes lead to negative or inconclusive results. Here we report the use of the Proximity Ligation Real-Time PCR (PLiRT-PCR) assay as an attractive and promising confirmatory method for the identification of semen and sperm proteins using two polyclonal antibodies, Prostate Specific Antigen (PSA) and Sperm-Specific Protein (SP10), respectively. PLiRT-PCR, relies on protein recognition by pairs of proximity probes (antibody-DNA conjugates) that give rise to a ligated DNA strand. The ligated DNA strand is then amplified and detected by qPCR.

Prevalence and causes of abnormal PSA recovery

BACKGROUND

Prostate-specific antigen (PSA) test is of paramount importance as a diagnostic tool for the detection and monitoring of patients with prostate cancer. In the presence of interfering factors such as heterophilic antibodies or anti-PSA antibodies the PSA test can yield significantly falsified results. The prevalence of these factors is unknown.

METHODS

We determined the recovery of PSA concentrations diluting patient samples with a standard serum of known PSA concentration. Based on the frequency distribution of recoveries in a pre-study on 268 samples, samples with recoveries <80% or >120% were defined as suspect, re-tested and further characterized to identify the cause of interference.

RESULTS

A total of 1158 consecutive serum samples were analyzed. Four samples (0.3%) showed reproducibly disturbed recoveries of 10%, 68%, 166% and 4441%. In three samples heterophilic antibodies were identified as the probable cause, in the fourth anti-PSA-autoantibodies. The very low recovery caused by the latter interference was confirmed in serum, as well as heparin- and EDTA plasma of blood samples obtained 6 months later. Analysis by eight different immunoassays showed recoveries ranging between <10% and 80%. In a follow-up study of 212 random plasma samples we found seven samples with autoantibodies against PSA which however did not show any disturbed PSA recovery.

CONCLUSIONS

About 0.3% of PSA determinations by the electrochemiluminescence assay (ECLIA) of Roche diagnostics are disturbed by heterophilic or anti-PSA autoantibodies. Although they are rare, these interferences can cause relevant misinterpretations of a PSA test result.

Repeated spurious elevation of serum prostate-specific antigen values solved by chemiluminescence analysis: A possible interference by heterophilic antibodies

Heterophilic antibodies are human immunoglobulins directed against various animal antigens. They can produce false-positive results in the analysis of different tumor markers, including prostate-specific antigen. This interference can lead to misdiagnosis, unnecessary tests, and overtreatment in some cases. We present herein the case of a 52-year-old man with repeated spurious elevation of prostate-specific antigen, reaching levels of 108.7 ng/mL, that were suspected to be caused by heterophilic antibodies. The interference was solved by changing the analysis technique. Real values of prostate-specific antigen were less than 1 ng/mL.

Spurious elevation of serum PSA after curative treatment for prostate cancer: clinical consequences and the role of heterophilic antibodies

BACKGROUND

Various interferences can cause spurious results for common laboratory tests. Although rare, heterophilic antibodies may produce false elevations in PSA that could prompt unnecessary therapy in men previously treated for prostate cancer. The aim of this study was to determine the prevalence of small, spurious PSA elevations, and the role of heterophilic antibodies.

METHODS

Phase I: all PSA tests drawn and measured between 27 October 2008 and 26 October 2010 at Vanderbilt University Medical Center were analyzed (n=17 133). Patients who had been treated for prostate cancer with PSA values that changed from undetectable to detectable were evaluated. Phase II: patients with a detectable PSA ≤0.5 ng ml(-1) measured between 24 October 2010 and 19 January 2011 were studied prospectively (n=1288). If any patient had a previously undetectable PSA value, their serum was tested for heterophilic antibody interference.

RESULTS

Phase I: 11 men had a spuriously elevated PSA after curative treatment for prostate cancer (0.3%). Mean time to PSA elevation was 3.4±5.5 years, and mean elevation in PSA was 0.33±0.28 ng ml(-1). Each patient's PSA was undetectable after being repeated, and no patient went on to unnecessary treatment. Phase II: 10 men had a newly detectable PSA, 9 of whom had a history of prostate cancer. Each tested negative for interfering heterophilic antibodies when their PSA test was repeated with a heterophilic antibody-blocking reagent.

CONCLUSIONS

In a large cohort, we estimate the prevalence of spuriously elevated PSA values in our population to be 0.3%. No patient with a prostate cancer history was subjected to unnecessary diagnostic evaluation or treatment. On prospective evaluation of PSA conversion to low detectable levels, no patient had evidence of interfering heterophilic antibodies. When using PSA for post-treatment surveillance, it is crucial to confirm all concerning values and consider the presence of a spurious elevation in PSA if the value does not correlate with the clinical scenario.