A multisystem composite biomarker as a preliminary diagnostic test in bipolar disorder

Objective Diagnosis and management of bipolar disorder ( BD ) are limited by the absence of available laboratory tests. We aimed to combine data from different molecular levels and tissues into a composite diagnostic and state biomarker. Methods Expression levels of 19 candidate genes in peripheral blood, plasma levels of BDNF , NT ‐3, IL ‐6 and IL ‐18, leukocyte counts, and urinary markers of oxidative damage to DNA and RNA were measured in 37 adult rapid‐cycling patients with BD in different affective states during a 6‐ to 12‐month period and in 40 age‐ and gender‐matched healthy individuals in a longitudinal, repeated measures design comprising a total of 211 samples. A composite biomarker was constructed using data‐driven variable selection. Results The composite biomarker discriminated between patients with BD and healthy control individuals with an area under the receiver operating characteristic curve ( AUC ) of 0.83 and a sensitivity of 73% and specificity of 71% corresponding with a moderately accurate test. Discrimination between manic and depressive states had a moderate accuracy, with an AUC of 0.82 and a sensitivity of 92% and a specificity of 40%. Conclusion Combining individual biomarkers across tissues and molecular systems could be a promising avenue for research in biomarker models in BD .