Prostate-specific antigen (PSA) is functionally and immunologically distinct from PAP. PSA is localized in both normal prostatic epithelial cells and prostatic carcinoma cells. PSA has proved to be the most prognostically reliable marker for monitoring recurrence of prostatic carcinoma; however, this test does not have the sensitivity or specificity (20%–40%) to be considered an ideal tumor marker. PSA velocity, the rate of change over time, PSA density, PSA value divided by prostate size, and various PSA isoforms (e.g., bound to protein) are used in an effort to provide better sensitivity and specificity. The gold standard for prostate cancer diagnosis, however, is the prostate tissue biopsy, although it is not 100% correct. PSA detects incidental as well as aggressive carcinomas. PSA is either free (fPSA; not attached to other proteins) or bound (attached to other proteins). Total PSA (tPSA) level includes both fPSA and bound PSA levels.Percentage of fPSA is a ratio of fPSA to tPSA; this gives an estimate of the probability of cancer in older than 50 years.

The most useful approach to date may be age-specific PSA reference ranges, which are based on the concept that blood PSA concentration is dependent on patient age. The increase in PSA with advancing age is attributed to four major factors: prostate enlargement, increasing inflammation, presence of microscopic but clinically insignificant cancer, and leakage of PSA into the serum (Table 6.10).

Testing for both PSA and PAP increases detection of early prostate cancer. The American Cancer Society recommends an annual digital rectal examination (DRE) and PSA test starting at age 40 years. PSA testing determines the effectiveness of therapy for prostate cancer and is used as an early indicator of prostate cancer recurrence. The greatest value of PSA is as a marker in the follow-up of patients at high risk for disease progression.

PSA lacks sufficient sensitivity and specificity to be used alone as a screening test for prostatic carcinoma, but in conjunction with a DRE, the detection rate of prostatic carcinoma is greatly increased, although still controversial.

Serum:

• Younger than 40 years old:

  • fPSA: <2.0 ng/mL or <2.0 μg/L

  • tPSA: ≤4.0 ng/mL

  • % of fPSA: >25%

Urine:

• PCA3 score

• PCA3 mRNA/PSA mRNA 35 copies/copy of PSA mRNA

• (PCA3 is a genetic marker)

• Percentage of fPSA = fPSA/tPSA × 100

• (Patients with prostate cancer have a lower proportion of fPSA compared with those who have benign conditions.)

1. Obtain a 5-mL venous blood serum sample (red-topped tube) or a urine specimen.

2. Observe standard precautions. Place the specimen in a biohazard bag.

3. Record patient’s age.

1. PSA increases occur with prostate cancer (80% of patients).

2. Patients with BPH often demonstrate tPSA values between 4.0 and 8.0 ng/mL (4.0 and 8.0 μg/L). Results between 4.0 and 8.0 ng/mL (4.0 and 8.0 μg/L) may represent BPH or possible cancer of the prostate. Results >8.0 ng/mL or >8.0 μg/L are highly suggestive of prostatic cancer.

3. Increases to >4.0 ng/mL or >4.0 μg/L have been reported in about 8% of patients with no prostatic malignancies and no benign diseases.

4. If a prostate tumor is completely and successfully removed, no antigen will be detected.

5. If the percentage of fPSA is <25%, there is a high likelihood of prostatic cancer.

Pretest Patient Care

1. Explain test purpose and procedure.

2. Do not schedule any prostatic examinations, including DRE, prostate biopsy, or TURP, for 1 week before the blood test is performed.

3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Transient increases in PSA occur following prostate palpation or DRE.

2. Increased PSA occurs with urinary retention.

3. Recent exposure to radioisotopes causes test interference.