Reducing assessment timing in Tap-Test-positive patients with iNPH: a 24-hour strategy and the exploratory role of the Symbol-Digit Modalities Test in surgical triage

We aimed to streamline the Tap Test in terms of timing and content in order to reduce the burdensome assessment in tap-test-positive patients and optimize the protocol of CSF-TT in iNPH, and strive for building explicit connection between CSF-TT and outcome of surgery. This retrospective cohort study enrolled a total of 69 inpatients with a positive Tap Test according to strict inclusion and exclusion criteria. Among them, 31 underwent the traditional Tap Test (T-TT, baseline-8–24 h-72 h) and 38 underwent the refined Tap Test (R-TT, baseline-24–48 h). All enrolled patients completed the same battery of assessments and ventriculoperitoneal shunt surgery. The positive predictive value (PPV) at different time points were compared between the two test versions using Chi-Square Test and Fisher’s exact test. The correlation between test results at each time point and surgical effectiveness was expressed using the phi coefficient, kappa value, and p-value. The magnitude of differences in mean scores for each measure between patients with effective versus ineffective surgery was analyzed using t-tests, p-values, and Cohen’s d. The outcome was collected on the outpatients’ records at 3–6 months follow-up. Among 69 probable iNPH patients, 63 sick people were diagnosed definite iNPH. The PPV of the R-TT was comparable to that of the T-TT (PPV: 92.11% vs. 90.32%, p = 1.00). No significant differences in PPV of time points were detected in T-TT (8 h vs. 24 h: p = 0.973; 8 h vs. 72 h: p = 1.00; 24 h vs. 72 h: p = 0.656), which is similar with that in R-TT (24 h vs. 48 h: p = 0.627). The assessment results at 24 h showed a strong correlation and agreement with surgical outcome (phi = 0.7073, kappa = 0.7039, p < 0.0001). The mean improvement in SDMT scores was significantly greater in the surgical responder group compared to the non-responder group at 24 h (Cohen’s d = 0.927, t = 4.25, p = 0.001). Assessment at 24 h demonstrates the strongest concordance with postoperative outcomes among the evaluated time points and appears sufficient for efficient surgical triage in patients with probable iNPH. Within this framework, the SDMT shows the greatest discriminative capacity between surgical responders and non-responders, supporting its potential role as a practical adjunct measure. The assessment protocol proposed in this study offers a feasible and reproducible approach for clinical evaluation and treatment decision-making, with the potential to optimize healthcare resource utilization, and reduce patient burden.