Objective: Although growing interest exists in the bipolar spectrum, fully structured diagnostic interviews might not accurately assess bipolar spectrum disorders. A validity study was carried out for diagnoses of threshold and sub-threshold bipolar disorders (BPD) based on the WHO Composite International Diagnostic Interview (CIDI) in the National Comorbidity Survey Replication (NCS-R). CIDI BPD screening scales were also evaluated.
Method: The NCS-R is a nationally representative US household population survey (n=9282 using CIDI to assess DSM-IV disorders. CIDI diagnoses were evaluated in blinded clinical reappraisal interviews using the non-patient version of the Structured Clinical Interview for DSM-IV (SCID).
Results: Excellent CIDI-SCID concordance was found for lifetime BP-I (AUC=.99 kappa=.88, PPV=.79, NPV=1.0), either BP-II or sub-threshold BPD (AUC=.96, kappa=.88, PPV=.85, NPV=.99), and overall bipolar spectrum disorders (i.e., BP-I/II or sub-threshold BPD; AUC=.99, kappa=.94, PPV=.88, NPV=1.0). Concordance was lower for BP-II (AUC=.83, kappa=.50, PPV=.41, NPV=.99) and sub-threshold BPD (AUC=.73, kappa=.51, PPV=.58, NPV=.99). The CIDI was unbiased compared to the SCID, yielding a lifetime bipolar spectrum disorders prevalence estimate of 4.4%. Brief CIDI-based screening scales detected 67-96% of true cases with positive predictive value of 31-52%.
Limitation: CIDI prevalence estimates are still probably conservative, though, but might be improved with future CIDI revisions based on new methodological studies with a clinical assessment more sensitive than the SCID to sub-threshold BPD.
Conclusions: Bipolar spectrum disorders are much more prevalent than previously realized. The CIDI is capable of generating conservative diagnoses of both threshold and sub-threshold BPD. Short CIDI-based scales are useful screens for BPD.