EXPRESS: Serum calprotectin levels and other inflammation biomarkers in manic episode of bipolar disorder: A comparative study

Previous studies suggest that inflammation may be implicated in the pathogenesis of acute mania in bipolar disorder (BD). This case-control study aimed to evaluate the serum levels of calprotectin, a neutrophil activation biomarker, along with other complete blood count (CBC)-derived inflammation markers in the manic episode of BD compared to controls and to determine any relationship with the severity of manic symptoms. Fifty manic patients and 50 healthy controls matched for age, sex and body mass index were included in the study. The serum calprotectin levels were measured by ELISA. Pan-immune inflammation value (PIV), systemic immune-inflammatory index (SII), systemic immune-inflammatory response index (SIRI), neutrophil/lymphocyte ratio (NLR), and platelet/lymphocyte ratio (PLR) were also calculated using CBC. The Young Mania Rating Scale was used to assess the severity of clinical symptoms. The level of serum calprotectin was 1.67±0.69 ng/ml in the patient group and 0.95±0.25 ng/ml in the control group (p<0.001). The inflammatory markers PIV, SII, SIRI and NLR, but not PLR (p=0.450), were significantly higher in the patient group compared to the control group (p≤0.001 for all comparisons). The area under curve of the calprotectin and NLR score for manic episode were 0.852 and 0.809, respectively. A moderate positive correlation was found between calprotectin level and severity of manic symptoms. Our findings highlight the role of inflammation in the pathophysiology of BD during the manic episode, and suggest that calprotectin and NLR can serve as inflammation markers to distinguish manic episode of BD patients from controls.