The clinical utility of the immune status questionnaire as a marker of immune function among persons with schizophrenia

Objective Immune–inflammatory dysregulation contributes to the pathophysiology of schizophrenia and other chronic disorders. Interleukin-6 (IL-6) and C-reactive protein (CRP) are established inflammatory biomarkers, yet their blood-based assessments are costly, time-consuming, and invasive. The Immune Status Questionnaire (ISQ), a brief self-report measure, may offer a noninvasive alternative for identifying individuals who require further immune evaluation. This study examined the associations among ISQ, IL-6, CRP, and physiological factors in patients with schizophrenia. Methods This retrospective chart review included 94 patients with schizophrenia, among whom 74 completed both blood sampling and the ISQ assessment. Hierarchical linear regression and structural equation modeling (SEM) were used to examine associations between immune markers and physiological variables. Results ISQ and cholesterol significantly predicted CRP levels, whereas IL-6 and cholesterol remained significant in the final regression model. SEM confirmed these pathways, showing that age, ISQ, and cholesterol influenced CRP through IL-6 mediation. Receiver operating characteristic (ROC) analyses identified an ISQ cutoff score of 10 and an IL-6 threshold of 3.0 pg/mL, yielding an area under the curve of 0.59 and a negative predictive value of 72.2%. Conclusions The ISQ demonstrates modest but practical potential as a noninvasive preliminary screening tool for immune dysfunction in schizophrenia. Given its accessibility and low cost, the ISQ may complement laboratory testing during early clinical evaluation. However, due to the limited sample size and retrospective design, further large-scale, community-based studies are warranted to validate its reliability, discriminative ability, and broader clinical applicability.