Prostatic Acid Phosphatase (PAP), Acid Phosphatase

Sample

1. It is done on the serum of the patient.
   1. Separate the serum immediately to decrease the contact with RBCs.
   2. Can stabilize the sample by the addition of disodium citrate monohydrate, 10 mg/mL of the serum.
   3. Or add the 50 µL of acetic acid (5 mol/L) per mL of the serum to lower the pH to 5.4.
2. Separate serum immediately and perform the test.

Precautions for the sample

1. If there is a delay then add citrate buffer or acetic acid to get the pH of 5.4 to 6.2, otherwise, there will be a rapid loss of the enzyme activity.
2. 50% of the activity is lost if the sample is kept at room temperature for more than one hour.
3. Avoid hemolysis. Hemolysed sample is contaminated with isoenzyme and should be discarded.
4. The lipemic serum also interferes with the reading of the final result because of turbidity.
5. Can store at 4 C° or -20 °C.
6. The sample is unstable at a temperature of >37 °C.
7. The sample is also unstable at a pH of > 7.0.

Indication

1. For the diagnosis of prostatic carcinoma.
2. This is raised in prostatic carcinoma.

Pathophysiology

1. Acid phosphatase is a lysosomal enzyme.

2.  Prostatic acid phosphatase is a subtype of total Acid phosphatase.
3. The prostatic component is found in the lysosomes of the prostatic epithelium.
   1. This is a glycoprotein with a molecular weight of 100,000 with the biological half-life of 1.1 to  2.6 hours.
4. Very small amounts of Acid phosphatase found in the liver, RBCs, Spleen, Platelets, and bone marrow with the negligible quantity of Prostatic acid phosphatase.
5. The greatest activity is present in the prostate and it is the richest source. It gives a small amount in the blood of a healthy person.

6. AP is raised in 50 to 75 % of the cases with local invasion of prostatic carcinoma.
   1. AP is raised in >90 % of the cases of metastatic disease.
   2. Acid phosphatase has an optimal activity below a pH of 7.0.
   3. AP is unstable especially at room temperature at 37 °C and at a pH level of >7.0.
   4. AP activity is lost >50% in one hour at room temperature.
   5. Acidification of the serum to a pH of <6.5 will stabilize the enzyme.
7. Erythrocyte AP is inhibited by the formaldehyde and cupric ions,  to which Prostatic AP is resistant.
8. Tartrate-resistant phosphatase is very helpful in the diagnosis of hairy cell leukemia.
9. Prostatic acid phosphatase (PAP) is replaced by:
   1. The PSA (Prostatic specific antigen).
   2. Digital rectal examination.
   3. Transrectal ultrasonography.
   4. Surgical biopsy of the prostate for histopathology.
   5. Total body bone scan.

NORMAL

Source 1

• Total Acid phosphatase= 0 to 5.5 U/L
• Prostatic acid phosphatase level = 0 to 0.6 U/L (<2.8 ng/ml)

Source 2

• Adult / Elderly = 0.13 to 0.63 units/L
• Children = 8.6 to 12.6 units/L
• Newborn = 10.4 to 16.4 units/L

Source 3

• Prostatic acid phosphatase = <2.5 ng/mL (immunoassay)
  • Tartarate inhibition method = 0 to 0.6 U/L

Source 4

• 2.5 to 3.7 ng/mL (2.5 to 3.7 µg/L)

Increased AP is seen in :

1. Prostatic carcinoma.
2. Prostatic massage.
3. TUR.
4. Leukemia (Myeloid leukemia, and hairy cell leukemia).
5. Bone disorder e.g. Paget’s disease, metastatic carcinoma from breast and lung.
6. This is raised in osteoclastoma (Giant cell tumor), Osteoclastic tumors, and osteopetrosis.
7. Storage disorder e.g. Gaucher’s disease, Niemann picks disease.
8. Hyperparathyroidism with bone involvement.

• The importance of AP in the semen is very important to rule out the case of rape because of AP has a high concentration in the semen.
  • The swab from the victim is kept in the 2.5 ml of broth.
    • Or store in the normal saline. Freeze the sample and thaw before performing the test at 2 to 4 °C.
  • Store at room temperature or at 4 °C.
  • Specimen retain AP activity for one month.

NOTE: Please see more details in Acid phosphatase total.

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