From the Guidelines
PSA doubling time should be calculated using the formula: PSADT = ln(2) / slope, where the slope is obtained from a linear regression of the natural log of PSA on time, and at least three PSA measurements are taken over a period of at least 3 months, with each measurement at least 4 weeks apart, as recommended by the prostate specific antigen working group guidelines 1. To calculate PSA doubling time, it is essential to use PSA values that are ≥0.20 ng/ml and follow a rising trend. The maximum period for calculation should be 12 months to reflect the patient's current disease activity.
- The formula takes into account the natural logarithm of 2 divided by the slope obtained from fitting a linear regression of the natural log of PSA on time.
- All PSA values used in the calculation should be obtained using the same assay, preferably at the same laboratory.
- Serum testosterone concentration should be relatively stable over the period, and treatment that may affect PSA or prostate cancer should be constant.
- For patients treated with radiation therapy, nadir subtraction may be necessary to ensure comparable PSADT estimates across therapies, as recommended by the guidelines 1. The calculation of PSA doubling time is crucial in determining the aggressiveness of prostate cancer and guiding treatment approaches. A shorter doubling time may indicate more aggressive disease, while a longer doubling time suggests slower progression 1.
- A PSADT <3 months has been found to be a useful surrogate marker for prostate cancer-specific and overall survival in patients with relapse after radical prostatectomy or radiation therapy.
- PSADT serves as an independent prognostic marker for survival in patients with metastatic androgen-independent prostate cancer. It is essential to note that the methodology for calculating PSADT and its ability to predict disease-specific survival is still being studied, and a consensus has yet to be reached on its universal usage or exact method of calculation 1.
From the Research
Calculating PSA Doubling Time
To calculate the PSA doubling time, several methods can be used, as discussed in the study 2. The PSA doubling time is a significant parameter in assessing the progression of prostate cancer and can be useful in various clinical situations, including surveillance of prostatic tumors after initial diagnosis, prognostic factor before curative treatment, evaluation of the efficacy of curative treatment, and prognostic factor of tumor aggressiveness.
Methods of Calculation
- The most reliable method of calculating PSA doubling time involves using the PSA kinetic, which takes into account the change in PSA levels over time.
- Other methods, such as the PSA velocity, can also be used, but the PSA doubling time is considered more reliable.
- The study 2 discusses the various methods used to calculate the PSA doubling time and highlights its importance in clinical practice.
Clinical Applications
- The PSA doubling time can be used to monitor the progression of prostate cancer and adjust treatment accordingly.
- It can also be used to evaluate the efficacy of treatment and predict the likelihood of recurrence.
- The study 2 discusses the various clinical situations in which the PSA doubling time can be useful, including surveillance of prostatic tumors, prognostic factor before curative treatment, and evaluation of the efficacy of curative treatment.
Limitations and Considerations
- The calculation of PSA doubling time requires accurate and reliable PSA measurements over time.
- The study 2 highlights the importance of using a reliable method of calculation to ensure accurate results.
- Other studies, such as 3, 4, 5, and 6, discuss the use of PSA doubling time in various clinical contexts, including the treatment of metastatic castration-resistant prostate cancer, but do not provide direct information on the calculation of PSA doubling time.