Sensitivity and Specificity of Cerebrospinal Fluid Placental Alkaline Phosphatase in Germinoma: An 8 pg/mL Threshold

Background Cerebrospinal fluid placental alkaline phosphatase (CSF-PLAP) is useful in diagnosing intracranial germinomas. However, reports on CSF-PLAP in histological subtypes other than germinoma remain limited. The primary aim of this study was to retrospectively analyze cases with histological diagnoses in which CSF-PLAP levels were measured and evaluate the sensitivity and specificity of this test using the clinically applied cutoff value of 8 pg/mL. Methods We retrospectively analyzed 134 patients with intracranial disease who underwent CSF-PLAP testing for diagnostic purposes and had confirmed histopathological diagnoses without receiving any adjuvant therapy before, or between CSF-PLAP measurement and surgery. The cases were categorized as true positive (TP), true negative (TN), false positive (FP), false negative, or clinical germinoma. Diagnostic accuracy was evaluated based on sensitivity, specificity, and statistical comparisons between groups. Results Among the 134 analyzed cases, 30 were classified as TP, 99 as TN, and 5 as FP. Using the 8 pg/mL cutoff, CSF-PLAP testing demonstrated a sensitivity of 100% and a specificity of 95.2%. The mean CSF-PLAP level was significantly higher in the TP group than in the FP group, and the TP group participants were significantly younger than the FP group participants. No significant differences in CSF-PLAP levels or age were found between the TP and clinical germinoma groups, supporting their clinical equivalence. Conclusions CSF-PLAP using an 8 pg/mL cutoff demonstrates high diagnostic accuracy for intracranial germinoma. Recognition of potential false-positive results and consideration of sampling site may further improve clinical interpretation of CSF-PLAP measurements.