Acid Phosphatase (AP), Total and Prostatic Acid Phosphatase

 

Sample

1. It is done on the serum of the patient and performs tests within one hour.
   • How to get good serum: Take 3 to 5 ml of blood in the disposable syringe or a vacutainer. Keep the syringe for 15 to 30 minutes and then centrifuge for 2 to 4 minutes to get the clear serum.
2. Serum should be separated immediately from the RBCs and stabilize the serum by adding disodium citrate monohydrate and adding 10 mg/ml of the serum.
   1. You can add acetic acid (5 mol/L) or 50 µL for 1 ml of the serum. This will lower the pH of the serum to 5.4, where the sample is stable.
   2. With all these precautions, the serum is stable at 37 °C (at room temperature) for several hours and one week if the serum is kept in the fridge.
3. EDTA plasma is better because it stabilizes the acid phosphatase.
4. A morning sample is preferred.
5. Avoid hemolysis.
6. The sample is stable for 24 hours at 2 to 8 °C.
7. Try to do the test immediately.
8. If serum is acidified below a pH of 6.5, that will stabilize the enzyme.

Precautions

1. It has poor stability in whole blood.
2. ACP is unstable at room temperature >37 °C.
3. ACP is unstable if the pH is >7.0.
4. The serum is separated immediately, and the test is performed within one hour.
5. EDTA plasma is preferred that stabilizes the AP.
6. Avoid prostatic massage in the last 48 hours.
   1. Rectal examination, prostatic massage, urinary catheterization, or instrumentation of the prostate in the previous 2 days before the test may give false high values.
7. Hemolysis falsely raised the value and should be rejected.
8. The lipemic serum also gives false value.
9. 50% of activity lost if kept at room temperature.
10. Drugs leading to elevated AP level are:
    1. Androgens in females.
    2. Clofibrate and antilipiodemic drugs.
    3. Specimen received >15 minutes later after the collection and hemolyzed sample give false values.

Purpose Of The Test (Indications):

1. To diagnose the prostatic carcinoma by advising the estimation of Total acid phosphatase and the prostatic component.
   1. This test is more accurate in the diagnosis of advanced prostatic cancer than the early diagnosis.
2. These two enzymes stage prostatic carcinoma and monitor the effectiveness of treatment.
3. The test for acid phosphatase can be done on a vaginal swab in rape cases because the seminal fluid is rich in acid phosphatase.

Pathophysiology:

1. Acid phosphatase (AP) includes all phosphatases with optimal activity below a pH of 7.0. The prostatic AP has an optimum pH range of 5 to 6.
   1. AP is unstable, particularly at temperature >37 °C and pH level >7.0.
   2. The prostatic AP in serum is labile and may lose >50% of the AP in one hour at room temperature.
   3. If you do pacification of the serum to a pH <6.5, it will stabilize the enzymes.
2. Source of AP:
   1. 1. Acid phosphatase enzymes are found in various tissue lysosomes like the Prostate, bone, kidney,  platelets, semen, liver, and spleen, with the possible exception of RBCs.
         1. The prostate is the richest source. The majority of AP arises from the RBCs and prostatic tissue.
      2. Extralysosomal AP is also found in many cells.
      3. High levels are also found in white blood cells like monocytes and lymphocytes.
      4. Total acid phosphatase consists of a one-half prostatic component and the rest of the liver, disintegrating platelets, and RBCs.
      5. Acid phosphatase activity is 100 times more in the prostate than in other tissues, so the prostate is the richest source.
         

         Acid phosphatase distribution

3. Acid phosphatase (AP), derived from the prostate, has a pH optimum range of 5 to 6.
   1. All phosphatases have optimal activity below a pH of 7.0
   2. The difference in pH between acid phosphatase and alkaline phosphatase:

   3. 	Acid phosphatase	Alkaline phosphatase
      pH	5.0	>7.0

 

Acid phosphatase distribution in various tissues

4. As the prostatic component (PAP) is not raised in the early prostatic diseases, this is not a good screening enzyme.
5. Acid phosphatase is a lysosomal enzyme, so the prostatic enzyme is found in the lysosome of prostatic epithelium and is a glycoprotein.
   

   Acid phosphatase present in the lysosomes

6. Once prostatic cancer spreads, AP’s level starts rising and significantly raised when there is metastasis, particularly in the bone.
   1. The raised level in 80% of the patient with metastasis is age-related.
   2. It is raised in Prostatic carcinoma, particularly its prostatic component.
7. Total AP is raised in Bone diseases.
8. Prostatic acid phosphatase needs to be differentiated from the non-prostatic sources like RBCs source.
   1. Total AP = AP after tartarate inhibition = Prostatic AP.
   2. Some of the inhibitors discriminate between prostatic and nonprostatic AP.
   3. Prostatic AP is inhibited by the dextrorotatory tartrate ions when there is no action on the RBC isoenzyme AP.
   4. RBC AP is inhibited by the formaldehyde and cupric ions, where prostatic AP is resistant.

Normal

• Total acid phosphatase
  • 2.5 to 3.7 ng /mL or 2.5 to 3.7 µg/L.
  • or less than 3.0 mg /L.
• Prostatic acid phosphatase  =  <2.5 ng/mL (0 to 0.6 U/L).
• Another reference
  • Adult 0.13 to 0.63 units/L at 37 °C
  • or 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.
• Another source
  • Prostatic AP = 0 to 0.6 U/L.
  • RIA = 3 µg/L.
  • Immunoassay = <20 µg/L.

Moderately Raised Levels Seen In, Other Than Prostatic Carcinoma:

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

The Raised Level Is Seen In:

1. Significantly raised level seen in prostatic carcinoma.
2. Benign prostatic hyperplasia.
3. Prostatitis.
4. Metastatic carcinoma of the prostate.
5. Metastases to the bones.

The prostatic AP level is variable in the case of carcinoma prostate:

The AP values vary according to the methodology like RIA and immunoassay. The level of AP is related to the clinical staging of prostatic carcinoma.

1. 5% to 10% of the prostatic carcinoma confined to the prostate has an elevated level of AP.
2. 20% to 25% of the prostatic carcinoma shows elevated value with the extension of prostatic adenocarcinoma outside the prostatic capsules without distant metastasis.
3. 75% to 80% of the cases show elevated AP with bone metastasis.

Important Facts:

1. After the surgery, its level will drop in 3 to 4 days.
2. With estrogen, therapy takes 3 to 4 weeks to drop the level.
3. Acid phosphatase is not recommended for screening prostatic carcinoma because its level is not usually significantly raised until the tumor has metastasis.
4. Acid phosphatase is not advised in routine to diagnose prostatic carcinoma, in case the following parameters are recommended:
   1. Per-rectal digital examination.
   2. Transurethral ultrasound image.
   3. Histologic examination of the prostatic biopsy.
   4. Total body scan.
   5. The Prostatic specific antigen is advised.

Medicolegal Importance:

1. There is a high concentration in the semen, so its measurement is important in rape cases.
2. Take the vaginal swab, keep it in 2.5% of broth, and store at  4 °C or room temperature.
   1. Result: In noncoital ladies, its value is 10 U/L and in the coital lady is >50 U/L.

• However, PSA is more specific and sensitive than acid phosphatase.

Test Value For The Layman:

1. This test is advised for the diagnosis of prostatic cancer.
2. It can be advised in case of rape on the vaginal swab.