Frequency of Health-System Contact explains Lower Monoclonal Gammopathy Testing in Hispanic and Asian Adults: 719,251 Participants in the All of Us Research Program

Monoclonal gammopathy of undetermined significance (MGUS) is asymptomatic and detected only when serum protein electrophoresis, immunofixation, or a free light chain assay is obtained for another reason. Prevalence is characterized mainly in Black and White adults, in whom screening reports a 1.6- to 3.0-fold Black excess (Landgren, Blood 2006; Leukemia 2014); Hispanic and Asian data are sparse. Risk-stratified screening presupposes the index test is obtained comparably across the populations it would enroll, which has not been examined.

In the All of Us Controlled Tier (CDR v9) we studied 719,251 adults with neither myeloma nor MGUS, by self-reported race and ethnicity. The outcome was any recorded precursor assay. Proportions were standardized to the 2000 US standard population across six age bands, with rate ratios by the delta method (Table 1). Odds of testing were estimated by logistic regression across a prespecified sequence of models, distal to proximal — age and sex; insurance; education and income; health-system contact (visit count, duration of observation) — all fitted to one complete-case sample (Table 2). A parallel analysis was restricted to participants with a documented indication. Counts below 20 were suppressed.

Age-standardized, a precursor assay had been recorded in 2.03% of Hispanic and 1.76% of Asian participants, against 2.32% of White participants (rate ratios 0.87, 95% CI 0.84–0.91, and 0.76, 0.69–0.83). Across the model sequence the Hispanic odds ratio was 0.88 with age and sex, 0.84 with insurance, 0.84 with education and income, and 1.00 with health-system contact; Asian estimates were 0.78, 0.79, 0.79, and 1.04 (n = 441,611 and 373,120). Insurance, education, and income produced no attenuation, whereas health-system contact abolished both associations. Where an indication was documented, no difference remained after adjustment for age and sex (Hispanic OR 0.96, p = 0.11; Asian OR 1.00, p = 0.93). Among Black participants the standardized proportion was 2.36%, against 2.32% in White participants (rate ratio 1.01, 0.97–1.06), unchanged after adjustment for age and sex (OR 1.02, 0.98–1.06).

Lower testing in Hispanic and Asian adults is attributable to frequency of health-system contact rather than to coverage, education, or income, and is absent once an indication is documented, localizing it to steps preceding the clinical encounter. No difference was observed between Black and White adults on the same measure, indicating a group-specific finding rather than a general gradient. The populations tested least are those whose MGUS epidemiology is least characterized, so screening would be least likely to reach the groups it most needs to describe. These data offer no support for interventions directed at clinician ordering or at the cost of the assay; they favor attaching precursor testing to encounters that already occur, testable within a single health system.