To evaluate the real-world diagnostic utility of cerebrospinal fluid (CSF) protein 14-3-3 for prion disease in the modern diagnostic era.

CSF protein 14-3-3 has been incorporated into diagnostic criteria for Creutzfeldt–Jakob disease for decades. Advances in MRI and RT-QuIC enable earlier detection of prion disease, when neuronal injury biomarkers such as 14-3-3 may be below detection thresholds. To improve sensitivity, the US National Prion Disease Pathology Surveillance Center (NPDPSC) lowered the positivity threshold from ≥4,000 to ≥2,000 AU/mL in May 2022. The impact of this change on diagnostic performance remains uncertain.

We analyzed CSF biomarker data from 629 participants evaluated at academic centers (Washington University in St. Louis and Mayo Clinic; 2016–2025) for prion disease (definite, n=9; probable, n=37), non-prion rapidly progressive dementia (RPD; n=147), and typically progressive dementia (n=436). Biomarkers were measured using standardized NPDPSC protocols, including RT-QuIC and ELISA assays of 14-3-3 and total tau. Brain MRIs were assessed for prion-associated changes. Diagnostic performance was summarized using sensitivity, specificity, accuracy, and likelihood ratios. Survival was assessed using Cox models.

At the revised threshold (≥2,000 AU/mL), 14-3-3 showed high sensitivity (100%) but very low specificity (≤6.1%) and low accuracy (≤28.5%), with positive likelihood ratios approximating 1. Elevated 14-3-3 levels were common in non-prion RPD (93.9%) and typically progressive dementias (95.6%). In contrast, total tau (≥1,150 pg/mL), RT-QuIC, and MRI demonstrated high diagnostic accuracy. Higher 14-3-3 concentrations were modestly associated with shorter survival (HR 1.02 per 1,000 AU/mL), comparable to total tau but weaker than RT-QuIC and MRI. Using the prior cutoff (≥4,000 AU/mL), 14-3-3 showed limited specificity and accuracy; an optimized threshold (10,400 AU/mL) improved accuracy but remained inferior to other markers.

Despite its historically outsized role, CSF protein 14-3-3 provides no meaningful incremental diagnostic value and may no longer be justified as a diagnostic test for prion disease.