A total of 242,898 VA patients met eligibility criteria. Patients without valid priority status were considered to be non-veterans and were excluded from the study (n = 1,390); another 42 cases were dropped for utilization more than 31 days after date of death (post-mortem bereavement counselling is offered by the VA; continued illogical use suggests error). The final sample numbered 241,466 VA patients
There were 53,134 schizophrenia patients aged ≥ 50 years with valid priority status receiving care in the VA in FY02. These patients were age-matched in a 4:1 ratio with diabetes patients (n = 188,332). During matching, it was noted that there were not enough diabetes patients aged 50–52 to match 4:1 for all schizophrenia patients; this age group matched 2.5 diabetes patients per 1 schizophrenia patient. Among patients with schizophrenia, 25% (n = 13,025) were also diagnosed with diabetes leaving 40,109 patients in the schizophrenia-only group.
The sample included 2.2% female veterans and ranged in age from 50 to 104 years (mean = 60.7; SD = 9.5). Twenty-one percent (21%) of patients were of non-white race/ethnicity (African-American, Hispanic), 53% were white, and 26% had missing data on this measure. Over the 4 years of the study, 5.5% of patients were not seen in the VA during one or more fiscal years in which they were alive; 14.5% of the patients died (see Table ).
Sample Characteristics of VA Patients with Diabetes, Schizophrenia, or Both Diabetes and Schizophrenia (N = 241,466)
Characteristics varied by diagnostic group. Patients with diabetes only were more likely to be married (63%) or widowed (5.2%) compared to schizophrenia patients, whereas patients with schizophrenia, regardless of diabetes status, were more likely to have never married (diabetes 10% vs Scz-DM 34% vs schizophrenia 42%; chi-square(6) = 32,140; p < .0001). Patients diagnosed with schizophrenia were more likely to be female (schizophrenia: 3.4% female, Scz-DM: 3.4% female, diabetes: 1.8% female; chi-square(2) = 478; p < .0001). Diabetes patients had the lowest rates of death (13.7%; chi-square(2) = 589; p < .0001), compared to schizophrenia patients (16.3%) and Scz-DM patients (20.6%). Average primary care use (mean, SD) is shown in Figure .
Average Primary Care Use by VA Patients with Schizophrenia, Diabetes, or Both Conditions over 4 Years (N = 241,508).
Missing data on race was three times more common among diabetes patients relative to schizophrenia patients (diabetes 30% vs Scz-DM 8% vs schizophrenia 11% missing race data; chi-square(2) = 8774; p < .0001). In VA databases in 2002, race was recorded by a clinical observer in inpatient records and was rarely missing, while outpatient records were characterized by high rates of missing data. Because patients with schizophrenia are likely to be hospitalized for acute psychotic exacerbations, they had more opportunity to receive a valid code on this measure.
Among patients diagnosed with schizophrenia, 34% were also diagnosed with schizoaffective disorder, post-traumatic stress disorder (7%), bipolar disorder (4%), major depression (3%) or other psychosis (3%) on two or more occasions in the baseline year.
The Selim physical comorbidity score, minus diabetes, averaged 2.3 (SD = 1.6; range 0–15) for patients with diabetes alone, 2.1 (SD = 1.6; range 0–11) for patients with both index conditions, but 1.4 (SD = 1.5; range 0–13) for patients with schizophrenia alone. The average number of medication classes for which patients received prescriptions in the baseline year was 6.4 (SD = 4.5; range 0–33) for schizophrenia-only patients, 10.0 (SD = 5.3; range 0–36) for both conditions, 8.7 (SD = 4.7; range 0–42) for diabetes-only.
The preliminary cluster analysis produced 20 clusters with between-centroid distances ranging from 3.6 to 345.5. The final cluster analysis identified four distinct patterns of primary care visits over the 4-year study period (shown in figure ). The first cluster depicted Increasing use of primary care from an average of 6 to 13 visits per year. The second cluster contained patients whose trajectory of primary care use was Consistent, averaging approximately 4 visits per year. Cluster three profiled a trajectory of decreasing use of primary care at a low level (Low-decreasing), falling from about 3 visits per year to about 1.5 visits per year. The fourth and final cluster described a trajectory of high levels of primary care use decreasing sharply from 10 to 4.5 visits per year on average (High-decreasing).
Primary Care Trajectories over the period FY02–FY05 for VA Patients with Schizophrenia, Diabetes, or Both Conditions (N = 241,508).
While most patients were in the low-decreasing primary care cluster, cluster membership differed by diagnostic group, as illustrated in Figure . Patients with schizophrenia only were predominant in the Low-decreasing trajectory, those with diabetes-only dominated the Consistent use trajectory, and Scz-DM patients were the most numerous group in both the Increasing and High-decreasing trajectories. Consistent-use cluster membership was more common among diabetes patients (33%) than among Scz-DM (28%) or schizophrenia-only patients (19%). Patients with schizophrenia were more likely to experience the low-decreasing trajectory of primary care, 73% schizophrenia-only vs 54% Scz-DM vs 52% diabetes-only. High-decreasing primary care use was associated with diabetes, with or without schizophrenia: 10% of Scz-DM patients experienced this trajectory, 8% of diabetes patients, and 4% of schizophrenia-only patients.
Trajectories of Primary Care Use by Older VA Patients with Chronic Disease: Schizophrenia Only, Diabetes Only, or Both Schizophrenia & Diabetes.
An unadjusted model of mortality during the three years of follow-up estimated increased relative odds of death associated with membership in Low-decreasing primary care use compared to the Consistent-use cluster (OR = 3.8, 95% CI 3.7–4.0). Compared to patients with Consistent primary care use, patients in the Increasing-use trajectory had lower relative odds of death (OR = 0.50, CI95 .45–.55) while those with High-decreasing use had increased odds of death (OR = 2.5, CI95 2.3–2.6). The unadjusted model had a poor fit as assessed by the C-statistic of 0.64.
The adjusted model showed a significant interaction of diagnosis by primary care cluster (Wald chi-square(6) = 70.9; p < .0001) and a good fit (C-statistic = 0.78), with main effects of cluster and diagnosis. Additional factors associated with death during follow-up included loss of system contact (OR = 1.4), greater age (OR = 1.9 per decade), and increased comorbidity burden (OR = 1.1 per Selim physical comorbidity; 95% confidence intervals provided in Table ). Being married (OR = 0.69) or female (OR = 0.64) was protective. The changes in estimated odds ratios from the unadjusted to the adjusted model demonstrate that some variation in mortality risk is attributable to specific aspects of health care, including treatment of multimorbidity and prescriptions, but significant variation in mortality is attributable to variation in the use of primary care. Relative odds of death associated with membership in each diagnosis by primary care sub-group, relative to a single reference group of diabetes with consistent care, are shown in the table.
Characteristics Associated with Decreased Survival among VA Patients with Diabetes, Schizophrenia, or Both Diabetes and Schizophrenia (N = 241,466)
In the covariate-adjusted Cox proportional hazards model of survival time, the interaction of primary care cluster by diagnosis was again significant. Hazard rates of mortality were similar within diagnosis groups for patients with either Increasing or High-decreasing primary care. The hazard ratio of mortality for schizophrenia and Scz-DM, relative to diabetes only, was significantly greater when the patient was experiencing low-decreasing primary care, compared to other trajectories of primary care. Additional risk of diminished survival was imparted by loss of system contact (HR = 1.2), older age (HR = 1.7 per decade), and more physical comorbidity (HR = 1.2 per point on the Selim score). Marriage (HR = 0.74) and female gender (HR = 0.69) were protective, as was Increasing primary care use. Compared to consistent use-diabetes patients, patients with increasing use were at much less risk of shorter survival (HR = 0.26 for schizophrenia patients, HR = 0.48 for Scz-DM patients, and HR = 0.38 for diabetes-only patients). Survival curves are shown in Figure .
Survival Curves by Primary Care Cluster, Diagnostic Group.