Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting

Mehmet Murat Kırpınar; İrem Yıldırım; Sarp Yoldaş; Furkan Toksoy; Merve Rana Altunel; Zeynep Özge Dağoğlu; Cana Aksoy Poyraz; Ömer Faruk Demirel

doi:10.5455/PBS.20260602025249

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Original Research
Online Published: 19 Aug 2026

PBS. 2026; 16(3): 181-191

doi: 10.5455/PBS.20260602025249

Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting

Mehmet Murat Kırpınar, İrem Yıldırım, Sarp Yoldaş, Furkan Toksoy, Merve Rana Altunel, Zeynep Özge Dağoğlu, Cana Aksoy Poyraz, Ömer Faruk Demirel.

Abstract
Objective: Increasing evidence suggests that inflammatory processes may play a role in the pathophysiology of mood disorders. However, the diagnostic utility of inflammatory biomarkers in distinguishing bipolar from unipolar depression remains unclear.

Methods: This retrospective study included 810 inpatients diagnosed with bipolar disorder (n = 444) or unipolar depression (n = 366). Inflammatory markers, including CRP, neutrophil count, NLR, SII, and SIRI, were obtained within 24 hours of admission. Group comparisons, hierarchical logistic regression analyses, ROC analyses, and multivariable linear regression models were performed.

Results: Inflammatory markers were significantly elevated in bipolar mania compared to depressive groups. In logistic regression analyses restricted to depressive episodes, higher NLR (OR = 1.21, p = .004), SII (OR = 1.0006, p = .003), and SIRI (OR = 1.21, p = .021) were associated with bipolar depression; however, effect sizes were modest. Clinical variables, including hospitalization history and treatment exposure, demonstrated stronger associations with diagnostic classification. ROC analyses revealed poor discriminative performance for all markers (AUCs ≈ 0.55). In linear regression models, hospitalization frequency, lithium, and antipsychotic use were not associated with inflammatory markers, whereas valproic acid use was associated with lower levels (all p < .001).

Conclusion: Although inflammatory markers are associated with bipolar disorder, their ability to distinguish bipolar from unipolar depression is limited. These findings suggest that inflammatory biomarkers reflect state-dependent processes rather than stable diagnostic differences and therefore have limited value as standalone diagnostic tools.

Key words: Bipolar disorder, Depression, Inflammation, Biomarkers, Diagnostic differentiation

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How to Cite this Article

Pubmed Style

Kırpınar MM, Yıldırım �, Yoldaş S, Toksoy F, Altunel MR, Dağoğlu ZO, Poyraz CA, Demirel OF. Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. PBS. Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

Web Style

Kırpınar MM, Yıldırım �, Yoldaş S, Toksoy F, Altunel MR, Dağoğlu ZO, Poyraz CA, Demirel OF. Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. https://www.pbsciences.org/?mno=322987 [Access: September 04, 2026]. doi:10.5455/PBS.20260602025249

AMA (American Medical Association) Style

Kırpınar MM, Yıldırım �, Yoldaş S, Toksoy F, Altunel MR, Dağoğlu ZO, Poyraz CA, Demirel OF. Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. PBS. Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

Vancouver/ICMJE Style

Kırpınar MM, Yıldırım �, Yoldaş S, Toksoy F, Altunel MR, Dağoğlu ZO, Poyraz CA, Demirel OF. Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. PBS, [cited September 04, 2026]; Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

Harvard Style

Kırpınar, M. M., Yıldırım, . �., Yoldaş, . S., Toksoy, . F., Altunel, . M. R., Dağoğlu, . Z. O., Poyraz, . C. A. & Demirel, . O. F. (2026) Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. PBS, Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

Turabian Style

Kırpınar, Mehmet Murat, İrem Yıldırım, Sarp Yoldaş, Furkan Toksoy, Merve Rana Altunel, Zeynep Ozge Dağoğlu, Cana Aksoy Poyraz, and Omer Faruk Demirel. 2026. Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. Psychiatry and Behavioral Sciences, Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

Chicago Style

Kırpınar, Mehmet Murat, İrem Yıldırım, Sarp Yoldaş, Furkan Toksoy, Merve Rana Altunel, Zeynep Ozge Dağoğlu, Cana Aksoy Poyraz, and Omer Faruk Demirel. "Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting." Psychiatry and Behavioral Sciences Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

MLA (The Modern Language Association) Style

APA (American Psychological Association) Style

Kırpınar, M. M., Yıldırım, . �., Yoldaş, . S., Toksoy, . F., Altunel, . M. R., Dağoğlu, . Z. O., Poyraz, . C. A. & Demirel, . O. F. (2026) Inflammatory Biomarkers in Bipolar and Unipolar Depression: Associations and Diagnostic Performance in a Tertiary Inpatient Setting. Psychiatry and Behavioral Sciences, Online First: 19 Aug, 2026. doi:10.5455/PBS.20260602025249

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