Acid Phosphatase (AP): Total and Prostatic Acid Phosphatase

The Acid Phosphatase Test is a sophisticated biochemical procedure designed to gauge the activity of the acid phosphatase enzyme in various biological specimens. This enzyme is prevalent in multiple tissues and bodily fluids, including but not limited to blood, the prostate gland, bone, and liver. The test procedure involves incubating the sample with a specific substrate that the acid phosphatase enzyme can act upon, resulting in the release of a detectable product. The quantity of this product is directly proportional to the enzyme activity in the sample, and this can be quantified using advanced spectrophotometric or colorimetric methods. Historically, this test has been a cornerstone in medical diagnostics for a range of conditions such as prostate cancer, leukemia, bone disorders, and liver disease. Despite its declining usage in favor of more specific and sensitive diagnostic techniques, it remains a valuable tool in certain contexts. Notably, it serves as a presumptive test for semen, which can be crucial in forensic investigations. The test can be performed directly on a stain, an extract of a stain, or a 'wipe' of the stained material, providing valuable information in cases of alleged sexual assault.

Purpose of the Test

1. This test is conducted to diagnose prostatic carcinoma by measuring total acid phosphatase (TAP) and its prostatic component.
2. Additionally, this test is utilized for the detection of semen in forensic cases through a vaginal swab. The high concentration of acid phosphatase in semen serves as an indicator of recent sexual activity. A level of 50 U/sample or more is deemed as positive evidence of semen.

Sample Collection

For the assessment of total acid phosphatase (TAP) and prostatic acid phosphatase (PAP), a morning sample is typically preferred. Approximately 3 to 5 ml of blood is drawn into a vacutainer and allowed to clot. The blood is then centrifuged for 10 minutes at 4500 rpm to obtain clear serum. The test is conducted immediately, but the sample can be stored for up to 24 hours if maintained at 2-8º C.

Precautions

1. The sample exhibits poor stability in whole blood, hence the serum is immediately separated and the test is conducted within an hour.
2. The sample becomes unstable for the ACP test if the pH exceeds 7.0.
3. The sample is unstable for the ACP test at room temperature (above 37º C).
4. Hemolyzed serum can lead to false-positive results. Elevated values can be observed in hemolyzed serum.

Normal Values

• Total acid phosphatase (TAP): 2.5 to 3.7 ng/mL or less than 3.0 mg/L
• Prostatic acid phosphatase (PAP): less than 2.5 ng/mL (0 to 0.6 U/L)
• Other references:
  • Adult: 0.13 to 0.63 units/L at 37° C
  • Adult: 2.2 to 10.5 units/L (SI units)
  • Child: 8.6 to 12.0 units/mL at 30° C
  • Newborn: 10.4 to 16.4 units/mL at 30°C

Causes for Elevated Levels

1. Prostatic carcinoma
2. Prostatitis
3. Benign prostatic hyperplasia
4. Metastatic carcinoma of the prostate
5. Bone metastases

Conditions Other Than Prostatic Carcinoma That May Cause Moderately Elevated Levels

1. Hyperparathyroidism
2. Niemann-Pick disease
3. Sickle cell anemia
4. Prostatitis and Benign prostatic hyperplasia (BPH)
5. Any cancer that has metastasized to the bones
6. Urinary retention
7. Multiple myelomas
8. Myeloid Leukemia
9. Paget's disease
10. Liver conditions such as cirrhosis
11. Renal diseases
12. Thrombocytosis
13. Gaucher’s disease

Importance of Acid Phosphatase Test in Forensic Cases

The high concentration of acid phosphatase in semen makes its measurement crucial in rape cases. The following methods are employed for sample collection from the victim's body:

1. Direct aspiration or saline lavage
2. A vaginal swab is taken from the victim's vagina, and the sample is placed in 2.5% broth and can be preserved at 4° C.

The significance of acid phosphatase test for the layman

1. The test is conducted to identify the presence of prostatic carcinoma, a type of prostate cancer.
2. This procedure is also implemented in situations involving suspected rape or sexual assault.