What PSA level is considered undetectable after radical prostatectomy?

1. What the original claims say — a direct readout of competing statements

The analyses present three principal claims about “undetectable” PSA after prostatectomy: one set of recent salvage‑radiotherapy studies treats PSA <0.1 ng/mL as undetectable and prognostically favorable, reporting better biochemical progression‑free and metastasis‑free survival for patients reaching that nadir ^{[1] [5]}. A second, earlier line of evidence defines undetectable ultrasensitive PSA as ≤0.05 ng/mL and links that nadir to lower 5‑year recurrence risk ^[2]. A third viewpoint emphasizes very low assay thresholds such as <0.02 or <0.001 ng/mL used by some institutions, while reminding clinicians that definitions vary and that a PSA rise to 0.2 ng/mL on two tests is widely used as the biochemical recurrence threshold ^{[3] [4]}. These claims are factually consistent in showing better outcomes with lower nadirs, yet they diverge on numeric cutoffs and on how to apply ultrasensitive assays.

2. Why numbers differ — assay sensitivity, lab practice and timing explain the variation

The numerical disagreement arises from differences in assay lower limits of detection and laboratory reporting practices, as well as post‑operative timing of measurement. Modern ultrasensitive assays detect PSA at levels far below 0.1 ng/mL, prompting some centers to report values down to 0.001–0.02 ng/mL; others prefer coarser thresholds because lower cutoffs increase the risk of false positives and clinical overinterpretation ^{[3] [2]}. Guidance also stresses waiting at least 6–8 weeks after surgery before obtaining a baseline PSA because residual circulating PSA declines slowly; inconsistent timing and the use of different labs complicate comparisons across studies and clinical follow‑up ^{[6] [4]}. The practical consequence is that a single numeric “undetectable” label cannot be separated from the test used.

3. How studies use thresholds — research vs. routine practice split

Recent salvage radiotherapy research often operationalizes undetectable as <0.1 ng/mL and links that endpoint to improved 5‑year biochemical and metastasis‑free survival, even proposing that androgen‑deprivation therapy might be withheld in selected patients who achieve this nadir ^{[1] [5]}. Conversely, prognostic work using ultrasensitive PSA argues for ≤0.05 ng/mL as a meaningful nadir tied to lower recurrence risk, while cautioning that lowering the detection threshold inevitably raises false‑positive rates and may lead to overtreatment ^[2]. These differences reflect distinct study designs and clinical questions: some research asks whether a lower nadir predicts long‑term outcomes after adjuvant or salvage treatment, while routine practice emphasizes reproducible, actionable cutoffs for surveillance.

4. Clinical consequences — surveillance, recurrence definitions and patient counseling

For clinicians and patients the operational takeaway is clear: use consistent assays and timing and interpret single low measurements cautiously. The commonly accepted working definition of biochemical recurrence after prostatectomy remains PSA ≥0.2 ng/mL confirmed on repeat testing, which serves as the trigger for further staging and consideration of salvage therapy ^{[4] [3]}. Values below that threshold require contextual interpretation: a persistent PSA of 0.05 versus 0.15 ng/mL may carry different prognostic implications depending on the assay and trend over serial tests, so decisions about imaging or systemic therapy should be based on trajectories rather than one‑off ultrasensitive readings ^{[2] [6]}.

5. Bottom line and unresolved questions — how to apply evidence to practice

The evidence establishes that lower PSA nadirs after radical prostatectomy correlate with better outcomes, but it does not mandate a single numeric definition of “undetectable” for all settings. Practically, many centers and recent studies use <0.1 ng/mL, ultrasensitive research often cites ≤0.05 ng/mL, and specialized labs may report even lower detection limits (<0.02 or <0.001 ng/mL); biochemical recurrence is typically defined at ≥0.2 ng/mL ^{[1] [2] [3] [4]}. Clinicians should document the assay and timing, rely on serial measurements, and recognize that prospective randomized data are still needed to determine how ultrasensitive nadirs should change management decisions such as withholding androgen‑deprivation therapy after salvage radiotherapy ^[1].