Methods: We recruited 1819 adults from a demographically-diverse Internet panel and asked them to imagine they were diagnosed with Type 2 diabetes, had been maintaining good blood glucose control, and were now viewing the results of a set of blood tests (CBC, Hemoglobin A1c, and renal panel) in an online portal in between doctor’s visits. Following the format currently implemented in the patient portal of a major academic medical center, all tables showed test values, standard ranges, and units but did not show indicators for high or low values. We randomly varied whether the patient’s A1c was either 7.1% or 8.4%. We then assessed whether participants would recognize that the A1c value was out-of-range and what they would do about it. We also measured their numeracy and health literacy.
Results: Compared to more numerate participants, less numerate participants were significantly less able to identify that the A1c value reported in the standard test result tables was above the standard range. Among those scoring in the lowest tertile of subjective numeracy, 39% correctly identified the out-of-range result, versus 62% in the highest tertile (p<0.001). This effect persisted even after controlling for health literacy. Furthermore, less numerate participants’ intentions to call their doctor were not significantly influenced by whether the A1c value was 8.4% vs. 7.1%, while highly numerate participants adjusted their likelihood of calling their doctor’s office based on the test result.
Conclusions: Current tabular formats for providing test results to patients (e.g., through patient portals to electronic record systems) appear unable to meet these patients’ informational needs to even a minimal standard. Such failures undermine the value of providing test data. Our results document the need to develop test result displays that are intuitively meaningful, even to less numerate patients.