Prostate Specific Antigen

Prostate-specific antigen (PSA) appears in normal, benign hyperplastic, and malignant Prostatic tissue as well as in metastatic prostatic carcinoma. Serum PSA levels are used to monitor the spread of recurrence of prostate cancer and to evaluate the patient's response to treatment. This test is not a suitable screening procedure for prostate cancer.

Purpose

• To monitor the Course of prostate cancer and aid evaluation of treatment.

Patient preparation

• Explain to the patient that this test is used to monitor prostate cancer and the patient's response to treatment.
• Tell him that the test requires a blood sample. Explain who will perform the venipuncture and when.
• Explain that he may experience slight discomfort from the needle puncture and the tourniquet but that collecting the sample usually takes less than 3 minutes.
• Inform him that he needn't restrict food or fluids before the test.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml red-top tube.
• Place the sample on ice, and send it to the laboratory immediately.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Collect the sample either before digital prostate examination or at least 48 hours after examination to avoid falsely elevated PSA levels.
• Handle the sample gently to prevent hemolysis.

Reference values

Normal serum values for PSA should not exceed 2 ng/ml in males age 40 and younger and 4 ng/ml in men ages 41 to 61. In men over age 61, values should not exceed 7 ng/ml.

Abnormal findings

About 80% of patients with prostate cancer have pretreatment PSA values greater than 4 mg/m1. However, PSA, results alone don't confirm a diagnosis of prostate cancer. About 20% of patients with benign prostatic hyperplasia also have levels greater than 4 ng/ml. Further assessment and testing, including tissue biopsy, are needed to confirm cancer.

Interfering factors

• Hemolysis due to rough handling of the sample
• Excessive doses of chemotherapeutic drugs, such as cyclophosphamide, diethylstilbestrol, and methotrexate (possible increase or decrease)
• Digital prostate examination (false­high)