Acid Phosphatase

Acid phosphatase (ACP) - a group of phosphatase enzymes most active at a pH of about 5.0 - is found primarily in the prostate gland and semen and, to a lesser extent, in the liver, spleen, red blood cells, bone marrow, and platelets. This test is used to measure total ACP and the prostatic fraction in serum.

Purpose

• To detect prostate cancer
• To monitor response to therapy for prostate cancer; successful treatment decreases ACP levels

Patient preparation

• Explain to the patient that this test is used to evaluate prostate function.
• 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.
• Withhold fluorides, phosphates, and clofibrate. If they must be continued, note this on the laboratory slip.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml red-top tube.
• If a hematoma develops at the venipuncture site, apply warm soaks.
• Resume administration of medications discontinued before the test.

Precautions

• Don't draw the sample within 48 hours of prostate manipulation (rectal examination).
• Handle the sample gently to prevent hemolysis.
• Send the sample to the laboratory immediately. ACP levels decrease by 50% within 1 hour if the sample remains at room temperature without a preservative or is not packed in ice.

Reference values

Serum values for total ACP depend on the assay method and range from 0 to 3.7 ng/ml.

Abnormal findings

High prostatic ACP levels generally indicate the presence of a tumor that has spread beyond the prostatic capsule. If the tumor has metastasized to bone, high ACP levels are accompanied by
high alkaline phosphatase (ALP) levels, reflecting increased osteoblastic activity.

ACP levels rise moderately in prostatic infarction, Paget's disease (some patients), Gaucher's disease and, occasionally, other conditions, such as multiple myeloma. False results may occur if ALP levels are high because ACP and ALP are similar, differing mainly in their optimum pH ranges.

Interfering factors

• Hemolysis due to rough handling of the sample or improper sample storage
• Delayed delivery of the sample to the laboratory (Possible false-low or false­ normal)
• Fluorides, phosphates, and oxalates (Possible false-low)
• Clofibrate (possible false-high)
• Androgens in females (increase)
• Prostate massage, catheterization, or rectal examination within 48 hours of the test.