National Institutes of Health Stroke Scale Reporting in Medicare Claims Data: Reporting in the First 3 Years

BACKGROUND: Since 2016, hospitals have been able to document International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes for the National Institutes of Health Stroke Scale (NIHSS). As of 2023, the Centers for Medicare standardized mean difference score, 0.88), stroke certified (37.2% versus 8.0%; standardized mean difference score, 0.75), higher volume (mean, 80.8 SD, 92.6 versus 6.33 SD, 14.1; standardized mean difference score, 1.12), and had intensive care unit availability (84.9% versus 23.2%; standardized mean difference score, 1.57). Adjusted odds of documentation were lower for patients with inpatient mortality (odds ratio, 0.64 95% CI, 0.61–0.68; P <0.0001), in nonmetropolitan areas (odds ratio, 0.49 95% CI, 0.40–0.61; P <0.0001), and male sex (odds ratio, 0.95 95% CI, 0.93–0.97; P <0.0001). NIHSS was documented for 52.9% of Medicare cases versus 93.1% of registry cases, and 74.7% of Medicare NIHSS scores equaled registry admission NIHSS. CONCLUSIONS: Missing ICD-10-CM NIHSS data remain widespread 3 years after the introduction of the ICD-10-CM NIHSS code, and there are systematic differences in reporting at the patient and hospital levels. These findings support continued assessment of NIHSS reporting and caution in its application to risk adjustment models.