Relationship of functional health literacy to patients' knowledge of their chronic disease: A study of patients with hypertension and diabetes

Background: Inadequate functional health literacy is common, but its impact on patients with chronic diseases is not well described. Objective: To examine among patients with hypertension or diabetes the relationship between their functional health literacy level and their knowledge of their chronic disease and treatment. Methods: We conducted a cross-sectional survey of patients with hypertension and diabetes presenting to the general medicine clinics at 2 urban public hospitals. Literacy was measured by the Test of Functional Health Literacy in Adults. Knowledge of their illness was assessed in patients with diabetes or hypertension using 21 hypertension and 10 diabetes questions based on key elements in educational materials used in our clinics. Results: A total of 402 patients with hypertension and 114 patients with diabetes were enrolled. Mean (±SD) knowledge scores for patients with hypertension with inadequate (n=189), marginal (n=49), or adequate (n=155) literacy were 13.2±3.1, 15.3±2.2, and 16.5±2.3, respectively (range, 4- 20; P<.001). A total of 92% of patients with hypertension and adequate literacy levels knew that a blood pressure reading of 160/100 mm Hg was high compared with 55% of those in the lowest reading level (P<.001). Mean (±SD) knowledge scores for patients with diabetes with inadequate (n=50), marginal (n=13), or adequate (n=51) literacy were 5.8±2.1, 6.8±1.9, and 8.1±1.6, respectively (range, 1-10; P<.001). A total of 94% of patients with diabetes and adequate functional health literacy knew the symptoms of hypoglycemia compared with 50% of those with inadequate literacy (P<.001). Conclusions: Inadequate functional health literacy poses a major barrier to educating patients with chronic diseases, and current efforts to overcome this appear unsuccessful.