From the Guidelines
To determine the actual Prostate-Specific Antigen (PSA) level in a patient taking finasteride, you should multiply the measured PSA value by 2, as finasteride typically reduces PSA levels by approximately 50%. This adjustment is necessary to accurately interpret PSA results for cancer screening purposes, preventing potentially dangerous delays in prostate cancer detection due to artificially lowered PSA values 1. For example, if a patient on finasteride has a measured PSA of 2 ng/mL, their adjusted or "true" PSA would be estimated at 4 ng/mL.
The adjustment factor should be applied after at least 6 months of continuous finasteride therapy, as this is when PSA suppression reaches a steady state 1. This multiplication factor helps healthcare providers accurately interpret PSA results for cancer screening purposes. It's essential to maintain consistent use of this adjustment factor during ongoing PSA monitoring to ensure meaningful comparisons of PSA trends over time.
Some studies have shown that the effects of 5-ARIs on PSA before 12 months are variable, and the decline at 3 years was greater than 50% 1. However, the most recent and highest quality study recommends using a multiplier of 2 to adjust the PSA level in patients taking finasteride 1.
Key points to consider:
- Finasteride reduces PSA levels by approximately 50%
- The adjustment factor should be applied after at least 6 months of continuous finasteride therapy
- The multiplication factor helps healthcare providers accurately interpret PSA results for cancer screening purposes
- Consistent use of this adjustment factor is essential during ongoing PSA monitoring to ensure meaningful comparisons of PSA trends over time 1.
From the FDA Drug Label
In clinical studies, finasteride tablets reduced serum PSA concentration by approximately 50% within six months of treatment. To interpret an isolated PSA value in patients treated with finasteride tablets for six months or more, PSA values should be doubled for comparison with normal ranges in untreated men.
The actual PSA level when a patient is taking finasteride cannot be directly determined, as finasteride reduces serum PSA concentration by approximately 50%. To estimate the actual PSA level, the measured PSA value should be doubled for comparison with normal ranges in untreated men 2.
From the Research
Actual PSA Level on Finasteride
The actual Prostate-Specific Antigen (PSA) level when a patient is taking finasteride can vary. Studies have shown that finasteride can decrease PSA levels by approximately 40-50% 3, 4.
- A study published in 2016 found that PSA levels reduced by approximately 40% during finasteride therapy 3.
- Another study published in 1993 found that the median percentage change in PSA was -50% (5-95% range: -81% to +20%) after 12 months of finasteride treatment 4.
- A study published in 2006 found that finasteride decreased serum PSA by approximately 50% 5.
Interpretation of PSA Levels on Finasteride
It is recommended to double the PSA levels for interpretation in finasteride-treated patients 6.
- A study published in 1997 found that doubling the PSA levels in finasteride-treated patients allows for appropriate interpretation of PSA values and does not mask the detection of prostate cancer 6.
- Another study published in 2002 found that the magnitude of change in serum PSA after 1 year of finasteride challenge may be useful in diagnosing prostate cancer in patients with elevated PSA levels and prior negative prostate biopsy 7.
PSA Level Ranges on Finasteride
Studies have shown that PSA levels can vary widely in patients taking finasteride.
- A study published in 1993 found that at baseline, 72% of patients had PSA < or = 4.0 ng/ml, and after 12 months on finasteride, 75% had PSA < or = 2.0 ng/ml 4.
- Another study published in 2002 found that the baseline PSA level for the entire group was 6.32 ng/mL, and at 1 year, the PSA level had decreased to 3.73 ng/mL [-41.0%] 7.