Background <p>The potentially biasing impacts of low language fluency, illiteracy, and sensory impairments on cognitive test performance are unknown, which may have implications for understanding their roles in cognitive decline and dementia.</p> Aims <p>We investigated effects of these features on cognitive test item completion and performance among older adults in China, a multilingual country with high prevalence of illiteracy and sensory impairment.</p> Methods <p>We used cognitive test data from the Harmonized Cognitive Assessment Protocol of the China Health and Retirement Longitudinal Study conducted in 2018 (N = 9755, age 60 + years). We first tested associations of fluency in spoken Mandarin, literacy, and sensory impairment (hearing and vision) with missingness of cognitive items. We then tested for differential item functioning (DIF) in observed cognitive items by these features.</p> Results <p>We observed high levels of missing data in most cognitive test items – on average 13% and as high as 65%. Low fluency in spoken Mandarin, illiteracy, and impairments in hearing and vision were each associated with greater odds of missingness on nearly all tests. Partly because of differential missingness, there was minimal evidence of DIF by these features in items in which we expected a priori to find DIF (e.g., repetition of a spoken phrase among those with hearing impairment). Several cognitive test items exhibited statistically significant DIF, however there was minimal evidence of meaningful DIF.</p> Conclusions <p>Differential missingness in cognitive items by spoken language, literacy, and sensory impairments is potentially more of an inferential threat than measurement differences in test items.</p>