Prostatic Specific Antigen (PSA)
Sample
- This is done on the serum of the patient.
- A random sample can be taken.
- Take the sample before any prostatic procedure is done.
- The sample is stable at 2 to 8 °C for 2 weeks.
Precautions
- Rectal examination may elevate a minimal level. Take the sample before the rectal examination.
- Prostatic biopsy or transurethral resection of the prostate elevate the PSA level.
- Ejaculation within 24 hours of the sample taking will lead to high value.
- Take the history of urinary tract infection or prostatitis which will leave to an elevation of PSA. This will be five times and remains elevated for at least 6 weeks.
- Take the history of medication like Proscar may increase the PSA value.
Indication
- This is a tumor marker for the diagnosis of prostatic carcinoma.
- PSA along with prostatic acid phosphatase increases the detection of prostatic carcinoma.
- PSA is a good marker for the monitoring of the effectiveness of the treatment.
- PSA is the early indicator of recurrence.
Important: PSA has no sensitivity and specificity for the diagnosis of prostatic carcinoma.
- While in the ASCP manual this test is claimed as highly specific, highly sensitive, and relatively low cost.
PSA with rectal examination may diagnose nearly 90 % of the cancers. - PSA is an important tumor marker for prostate cancer:
- It can diagnose.
- It can stage.
- It can monitor the treatment of prostate cancer.
Pathophysiology
- PSA is a glycoprotein present in the cytoplasm of the epithelial cells and ducts of the prostate and in the prostatic carcinoma.
- PSA is a kallikrein-serine proteinase produced by the prostate epithelial cells and from malignant prostatic cells.
- PSA is a single chain glycoprotein found in high concentrations in the prostate.
- Its molecular mass is 28.43 kD.
- It consists of 237 amino acids.
- The gene coding is done and it is present on chromosome 19.
- This is an antigenic protein.
- PSA possesses chymotrypsin and trypsin-like activity.
- PSA is present in the blood in two forms:
- Free PSA.
- PSA bound to protein.
- In BPH there is more free PSA, while in cancer there is more bound PSA.
- It is produced by the epithelial cells of acini and prostate gland ducts.
- PSA is secreted into the prostatic ducts.
- In the seminal fluid, PSA cleaves seminal vesicle-specific protein into small low molecular weight proteins.
- The above process leads to the liquefaction of the seminal coagulum.
- Raised level of PSA with increasing age depends upon the following factors:
- Enlargement of the prostate.
- Inflammation of the prostate.
- Presence of microscopic foci of carcinoma which are clinically insignificant.
- Leakage of PSA into the serum.
- Level > 4 ng/mL are found in more than 80% of the cancer cases.
- The level of PSA also denotes the tumor burden.
- Surgery, radiation, or hormone therapy are associated with a decrease in PSA level.
- Later on, an increase in the PSA level indicates the recurrence of the tumor.
- The US preventive services Taskforce recommendation are :
- No use of screening by doing PSA after the age of 75 years.
- They also say that there is a limited value of PSA for screening under the age of 75 years unless there is strong family history.
- Their recommendation is PSA screening every 4 years instead of annual screening.
- While the American urological society and American cancer society have a different recommendation.
- They recommend an annual PSA screening test after the age of 50 years.
- In the people with strong family history and men Afro-American, advise PSA at the age of 40 years.
- PSA has a long half-life of 2 to 3 weeks when serum comes to a normal level or baseline after any procedure on the prostate.
- PSA levels may not be raised in the early stages of Prostatic carcinoma.
- PSA has a limited value of diagnosis in the gray zone of 4 to 10 ng/mL
- Benign prostatic hyperplasia show values of 4 to 8 ng/mL.
- Level > 8 ng/mL are highly suggestive of prostatic cancer.
- Low level is due to benign prostatic hyperplasia or early prostatic cancer.
- If Prostatic cancer is completely removed, then PSA will not be detected.
- Patients with a level below 10 ng/mL have the local disease and respond well to local treatment.
- After complete curative surgery or radiation therapy, the PSA level will be between 0 to 0.5 ng/mL.
NORMAL
Source 1
Healthy male: % of the population | ng/mL |
80% | <4.0 |
18% | 4.1 to 10.0 |
2% | 10.1 to 20 |
1% | >20 |
- To convert into SI units x 1.0 = µg/L
Source 3
- Men = <4.0 ng/mL
- PSA value increases with age.
Another source
- Healthy Male less than 40 years of age = 0 to 2.5 ng/mL
- Healthy males above 40 years of age :
- < 4.0 ng/mL in 96 %.
- 4 to 10 ng/mL in 4 %
- Benign Prostatic Hyperplasia
- <4 ng/mL in 90 %.
- 4—10 ng/mL in 10 %.
- > 10 ng/mL in 1 %
- Prostatic cancer :
- < 4 ng/mL in 15 % .
- 4 – 10 ng/mL in 20 %.
- > 10 ng/mL in 65 %
- Free PSA = more in BPH.
- Bound PSA = more in cancers.
- Free PSA <25%, then more chances of cancer.
Source 4
- PSA : Men = 0 to 4.0 ng/mL or 0 to 4.0 µg/L
- 4.0 to 8.0 ng/mL suggests Benign prostatic hyperplasia or possible prostatic Cancer.
- >4.0 ng/mL is reported in 8% of the cases with no malignancy and no benign disease.
- >8.0 ng/mL are highly suggestive of prostatic cancer.
If prostatic cancer is completely removed, then no PSA will be detected.
-
- The suggested age-specific PSA reference ranges:
- 0 to 2.5 ng/mL for 40 to 49 years.
- 0 to 3.5 ng/mL for 50 to 59 years.
- 0 to 4.5 ng/mL for 60 to 69 years.
- 0 to 6.5 ng/mL for 70 to 79 years
- The suggested age-specific PSA reference ranges:
Increase PSA has been seen in:
- Prostatic cancers.
- Benign prostatic hyperplasia.
- Prostatitis.
- Prostatic infarction.
- In the case of rectal manipulation of the prostate.
Relationship of free PSA for the possibility of cancer
Free PSA % | The possibility of cancer in % |
---|---|
0 to 10 | 56 |
10 to 15 | 28 |
15 to 20 | 20 |
20 to 25 | 16 |
>25 | 8 |
Recommendation for PSA
- This has high specificity, high sensitivity, and low cost.
- Men over the 50 years are advised for early diagnosis:
- PSA.
- Rectal examination.
- PSA correlates with pathological stages of tumor extension and metastasis.
- Higher PSA level is associated with the advanced pathological stage.
- Tumor confined to the prostate has seldom PSA >50 ng/mL.
- PSA level <20 ng/mL has rarely bone metastasis.
- After surgical treatment the response will be:
- After radical prostatectomy = PSA level be below the detection limit.
- This drop will take 2 to 3 weeks after the surgery.
- Measure the PSA first year after the surgery = every third month.
- Measure the PSA second years after the surgery = every fourth month.
- Measure the PSA third year after the surgery = every 6 months.
- After one year of the surgery, 50% of the cases show a rise in the PSA level indicating positive biopsy and
- metastasis.
- After radical prostatectomy = PSA level be below the detection limit.
- Antiandrogen therapy includes:
- Bilateral Oophorectomy.
- LH- releasing hormone analog-like diethylstilbesterol and Flutamide is given.
- Importance: Tumor confined to the prostate is curable by the surgery, therefore early detection is very important.