How long after robotic prostate surgery should PSA remain undetectable?
Executive summary
After robotic radical prostatectomy the prostate — the main source of PSA — is removed and PSA is expected to fall to very low or undetectable levels within weeks to a few months; most guidelines and patient resources report undetectable (commonly <0.1 ng/mL, sometimes <0.05 ng/mL depending on the lab) by about 4–8 weeks, but recent large-cohort work and expert comment argue clinicians should wait longer (around three months) before labeling PSA as persistently detectable and acting on it [1] [2] [3] [4] [5].
1. What “undetectable” means and why assays matter
“Undetectable” is not a single universal number: many labs report values <0.1 ng/mL as undetectable while high-sensitivity assays can detect down to 0.03–0.05 ng/mL, so whether a post‑surgery PSA is called undetectable depends on the assay and reporting threshold used by the institution [4] [6] [7].
2. The conventional timeline after surgery
Clinical practice and patient-facing organisations typically advise that PSA should fall to very low or undetectable levels within about 4–8 weeks after radical prostatectomy because PSA’s serum half‑life is short (around 3.2 days), meaning residual circulating PSA clears over weeks [1] [3] [6]. The American Cancer Society and national cancer charities commonly recommend waiting at least 6–8 weeks before the first PSA check so that lingering PSA from preoperative production has time to clear [2] [8].
3. Why some experts say to wait longer before acting
A large cohort analysis from Mass General Brigham highlights that checking too early — the common practice of 1.5–2 months — can mislabel patients as having persistent PSA and prompt unnecessary salvage radiation or hormone therapy; their data suggest monitoring for at least three months before concluding PSA persistence, especially for men with high preoperative PSA [5]. This reflects a tension between early detection of true residual disease and the risk of overtreatment driven by transiently detectable PSA levels.
4. How follow‑up testing is typically scheduled
After robotic prostatectomy many urologists schedule PSA checks every three months in the first year, every six months in the second, then annually if stable — a cadence intended to capture early rises while allowing time for borderline or transient signals to clarify [9]. Imaging and salvage therapy decisions are commonly tied to confirmed, consecutive rises in PSA (for example two rising values or reaching specific thresholds such as ~0.2 ng/mL in some protocols) and may prompt PSMA PET imaging or radiotherapy when the pattern suggests true biochemical recurrence [1] [3].
5. What a later detectable PSA typically implies
A PSA that becomes detectable months or years after an initially undetectable result often indicates prostate cells remain somewhere in the body — most commonly residual local or metastatic cancer cells — and is termed biochemical recurrence; population studies and reviews show that 20–40% of men may experience a PSA rise within years after surgery, and the timing and doubling time of that rise influence prognosis and treatment choices [10] [6] [7]. However, isolated low-level detectable PSA that does not rise over time may not always signal clinically significant disease, underscoring the importance of repeat measures and context [2] [4].
6. Bottom line — practical guidance distilled from the evidence
Expect PSA to be very low or undetectable by roughly 4–8 weeks after robotic prostatectomy if the operation removed the prostate entirely and labs use a conventional threshold, but clinicians and recent large studies recommend confirming clearance over a longer window — commonly at least three months — before labeling PSA as persistently detectable and initiating salvage therapy; assay sensitivity, preoperative PSA, pathology (e.g., positive nodes), and serial trends are essential to interpret any detectable value [1] [2] [3] [5] [6] [4].