Comment:

I have used the free PSA ratio (%fPSA) for years because it provides a reliable, cost-effective method to triage patients hovering in the PSA gray zone without immediately resorting to invasive procedures. Despite it being clear in the literature for decades, it is rare that I see it being used. The relatively recent availability of multiparametric MRIs has added a helpful tool to save men from unnecessary biopsies, however it still, as any tool, has a significant amount of false positive and false negatives. This retrospective analysis confirms that the %fPSA can effectively synergize with the MRI for improved accuracy.

Before the advent of multiparametric MRI, when I utilized the free PSA ratio as a primary standalone screening tool for men in the PSA gray zone, we faced this exact same structural constraint. A serum marker can’t perfectly distinguish between benign glandular hyperplasia and an organ-confined malignancy. When deployed as a generalized first-line screen across all stages, a highly sensitive 25% cutoff successfully flags roughly 95% of cancers, although the cutoff changes with age. Yet, this still guarantees a 5% false-negative rate, meaning we inherently miss one in twenty malignancies. More devastatingly, this threshold carries a massive false-positive rate approaching 80%. Historically, relying exclusively on %fPSA without prior structural imaging meant channeling the vast majority of healthy men into an unnecessary biopsy.

However, analyzing the inherent sensitivity and specificity of %fPSA exposes a profound diagnostic hazard depending on where we set the threshold. If we adopt the traditional 20% cutoff, the assay yields a 91.9% sensitivity but a dismal 46.8% specificity. While this reduces the false-negative hazard (missing only 8.1% of cancers), it balloons the false-positive rate to 53.2%, channeling a massive number of healthy men into an unnecessary biopsy. Tightening the threshold to 17.6% drops the false-positive rate to 36.3%, but forces us to accept a higher 13.5% false-negative rate. The definitive takeaway is that there is no perfect threshold; we must carefully wield %fPSA to balance the necessity of finding lethal disease against the structural trauma of over-biopsying, a pragmatic reality that expensive newer tests have yet to solve.

The Wonk Debate – Audio Critique & Clinical Commentary:

Summary:

Clinical Bottom Line

This diagnostic accuracy study suggests that in men with a “negative” or “low-risk” prostate MRI (PI-RADS <3) and PSA levels in the gray zone (≤10 ng/ml), a free PSA ratio (%fPSA) cutoff of 17.6% can effectively triage patients for biopsy. Implementing this threshold could identify 86.5% of clinically significant cancers (CSC) that might otherwise be missed by relying on MRI alone, while potentially sparing approximately 64% of patients with benign findings from unnecessary invasive procedures. While %fPSA is an older biomarker, this study provides a practical, cost-effective strategy for a common clinical dilemma where expensive newer markers (like PHI or 4K) may not be available.

Results in Context

• Main Results: Using a %fPSA cutoff of 17.6%, the study found a sensitivity of 86.5% and a specificity of 63.7% for detecting CSC.
  
  
• Performance Metrics: * Area Under the Curve (AUC): The %fPSA performed significantly better (AUC = 0.757) than total PSA (AUC = 0.393) or absolute free PSA (AUC = 0.611) in this specific patient population.

• Detection Rates: CSC was found in 34% of patients with %fPSA <17.6%, compared to only 4% of patients with %fPSA >17.6%.
  

• Definitions: * Clinically Significant Cancer (CSC): Defined as Gleason grade group (GGG) ≥ 2.
  

• PI-RADS <3: Refers to MRI findings where CSC is considered unlikely (scores of 1 or 2).
  

• Biomarker Context: %fPSA (free PSA divided by total PSA) is a readily available, low-cost serum marker used to differentiate prostate cancer from benign prostatic hyperplasia (BPH).
  
  
  

Assertive Critical Appraisal

• Appraisal of Biomarker Claim: This is a prognostic/diagnostic biomarker study. The authors successfully demonstrate that %fPSA adds value after an MRI has been performed, addressing the clinical gap of “MRI-negative” patients who may still harbor significant disease.
  
  
  

Reporting Quality Assessment (REMARK):

• Strengths: The study clearly specifies the patient population (PI-RADS <3, PSA \le 10), the assay used, and uses ROC analysis to determine the optimal cut-point.
  
  
• Weaknesses: As a single-center retrospective analysis, the 17.6% cutoff may be subject to “overfitting” to this specific cohort and requires external validation before being adopted as a universal standard.
  
  

• Trade-offs in Cutoffs: The authors compared the 17.6% threshold against traditional 15% and 20% cutoffs.
  

• 15% cutoff: Higher specificity (75.4%) but lower sensitivity (67.6%), meaning more cancers would be missed.
  
• 20% cutoff: Higher sensitivity (91.9%) but very low specificity (46.8%), leading to many unnecessary biopsies.
  
• The 17.6% threshold was selected as the most “informative” based on Likelihood Ratios (LR).
  

• Applicability: These findings are highly relevant to general urology and primary care. Because %fPSA is significantly cheaper than newer genomic tests or the PHI test, it represents a high-value “triage” step in healthcare systems with limited resources.
  
  

Research Objective

To evaluate the diagnostic performance of the free PSA ratio in detecting clinically significant prostate cancer in patients with a PI-RADS score <3 and total PSA levels \le 10 ng/ml.

Study Design

Retrospective diagnostic accuracy study analyzing 1,435 biopsies. A sub-cohort of 208 patients meeting the specific MRI and PSA criteria was used for the primary analysis. All patients underwent systematic biopsy following MRI.

Setting and Participants

• Setting: Single institution (Yonsei University, Seoul, Korea) between April 2018 and January 2023.
  
• Participants: Men with PI-RADS <3 and PSA between 4 and 10 ng/ml.
  
• Median Age: 65 years.
  
• Median PSA: 5.06 ng/ml.
  

Bibliographic Data

• Title: Usefulness of free PSA ratio to enhance detection of clinically significant prostate cancer in patients with PI-RADS<3 and PSA≤10
• Authors: Ji Eun Heo, Hyun Ho Han, Won Sik Jang, Won Sik Ham, Woong Kyu Han, Young Deuk Choi, Jongsoo Lee
  
• Journal: Prostate International
  
• Year: 2025
  
• DOI: https://doi.org/10.1016/j.prnil.2024.12.001