Diagnostic performance of increased prolidase activity in schizophrenia

• Prolidase activity may be a diagnostic marker for schizophrenia.
• Prolidase level 392.65 U/L could be a valid diagnostic measure.
• Increased prolidase activity is related to the pathogenesis of the disease regardless of antipsychotic medications.

We investigated whether prolidase activity has a diagnostic test value in schizophrenia and assessed the relation between prolidase activity and sociodemographic-clinical characteristics of patients with schizophrenia. Fifty patients with schizophrenia (diagnosed as schizophrenia according to DSM-V criteria) and 50 healthy volunteers were included in this study. Case and control groups had a similar distribution in age, sex, body mass index (BMI), and smoking status. Serum prolidase activity was measured in both groups and was determined to be significantly higher in the patient group (509.706 ± 41.918) compared to the control group (335.4 ± 13.6; t = 6.231; p = 0.0001). A cut-off point of 392.65 U/L prolidase was determined for diagnostic measures from the plotted ROC curve. The area under the ROC curve was 1.000, which was significant (p < 0.0001). Higher values were assigned as the disease state. Both positive predictive value (PPV) and negative predictive value (NPV) were 100% at the cut-off point of 392.650 U/L. The prolidase levels of the control group were all below the cut-off point. There were no statistically significant differences between the two groups with regard to age, gender, or BMI (p > 0.05), and no correlation was found between mean prolidase activity and age of onset of the disease, family history, disease duration, number of hospitalizations, subtypes of schizophrenia, PANSS scores or sub-scores, CGI-S scores, S-A scale scores, and the antipsychotic treatment (p > 0.05). The results of this study indicate that serum prolidase activity may be a useful diagnostic test for schizophrenia; however, further studies are needed to verify this.