Utilization Patterns and Net Direct Medical Cost to Medicaid of Irritable Bowel Syndrome

Bradley C. Martin; Rahul Ganguly; Sandhya Pannicker; Feride Frech; Victoria Barghout


Curr Med Res Opin. 2003;19(8) 

In This Article


The complete Medicaid claims databases for the 5% California sample and the entirety of North Carolina described 85 557 and 471 796 persons, respectively, aged 18 or older. A total of 492 California and 2215 North Carolina Medicaid recipients met the definitive IBS case definition. The final study cohort, after nonambulatory recipients were eliminated, included 475 and 2071 IBS case-control pairs from California and North Carolina, respectively. No significant within-state differences in demographic or Medicaid eligibility characteristics were noted between the IBS cases and controls ( Table 1 ). Consistent with the published literature, both states demonstrated a substantially greater percentage of women with IBS than men with IBS (75% and 86% in California and North Carolina, respectively).[1,2,4,5] IBS patients from California were slightly older than IBS patients from North Carolina. Most subjects (more than 80%) in both states were continuously enrolled during the 12-month period following the index date.

The prevalence of comorbid conditions among the study subjects is presented in Table 2 . For many conditions, the IBS cases had a higher comorbidity burden than did controls. This was particularly true for chronic obstructive pulmonary disease (p < 0.0001 in both states) and mental conditions such as psychoses (p ≤ 0.01 in both states) and depression (p < 0.0001 in both states). Peptic ulcer disease (p < 0.0001 in both states) and fluid and electrolyte disorders (p < 0.05 in both states) also were significantly more common among IBS cases than controls. The average comorbidity scores (i.e. 1-year predicted costs based on the summation of weights assigned for each comorbid condition) for IBS cases and controls were $2793 and $2382 (p = 0.1140) in California and $3386 and $2663 (p < 0.0001) in North Carolina, respectively.

Patients with IBS received a significantly higher number of prescriptions and had a greater number of physician and outpatient visits in California and North Carolina than did non-IBS controls (p < 0.0001) ( Table 3 ). The number of physician visits for IBS patients in both states was almost double that for controls. Outpatient visits for IBS cases compared with controls were doubled in California and quadrupled in North Carolina. Whereas twice as many inpatient visits for IBS cases versus controls were observed in North Carolina (0.55 vs 0.29 claims per person per year; p < 0.0001), the difference in California was not significant. Mean numbers of inpatient days per patient per year were similar for IBS cases and controls in both states. Among California recipients, use of 'other health care services' (not otherwise categorized) was significantly more frequent for IBS cases than for controls (p < 0.0001). This was not the case in North Carolina, however (p = 0.06).

For most categories of service, IBS cases had greater mean Medicaid expenditures PMPY than did matched controls ( Table 4 ) in both states. The unadjusted net annualized expenditures PMPY attributed to IBS were $962 for California and $2191 for North Carolina, amounting to 48% and 59% increases in Medicaid expenditures versus matched controls, respectively. Most of the additional Medicaid costs associated with IBS (77% for California, 70% for North Carolina) were attributable to spending for ambulatory care, including prescription drugs and physician and outpatient visits.

Multivariate adjustment for the predefined parameters (case-control dummy variable, Medicare eligibility dummy variable, age in years and [age in years],[2] sex dummy variable, and race) and comorbidity score had a modest impact on the estimation of net expenditures attributable to IBS. Adjusted net incremental expenditures ( Table 4 ) were generally lower than their unadjusted counterparts. However, the same general trend was observed for nearly all categories of expenditures in both states (except 'other' expenditures in North Carolina). The net adjusted incremental expenditures associated with IBS were $838 for California and $1630 for North Carolina, corresponding to 42% and 43% increases in Medicaid expenditures compared with those of matched controls, respectively. Overall, the models had good measures of fit.

Table 5 lists the mean recipient expenditures and the net unadjusted and adjusted IBS-related net incremental expenditures by age, sex, and race for cases and controls. In North Carolina, men tended to have higher adjusted net incremental Medicaid expenditures than women ($2815 vs $1469, respectively). Only a minimal difference between sexes was observed in California. The impact of race on IBS-related expenditures in the two states was statistically inconclusive. Persons between the ages of 41 and 65 consistently had higher net expenditures than did persons who were older than 65 or younger than 41.

Sensitivity analysis using the probable IBS case definition resulted in 1050 and 1720 additional cases from California and North Carolina, respectively. Adding the IBS cases identified in the final cohort to the probable IBS cases resulted in as many as 1525 and 3791 patients with IBS in the 5% California and North Carolina samples, respectively. These numbers are equivalent to 19.4 and 8.3 IBS cases per 1000 Medicaid recipients in California and North Carolina, respectively. In North Carolina, annualized mean total expenditures for probable IBS cases were $5726 PMPY (95% CI 5358-6094), with a net unadjusted IBS-related incremental expenditure of $1840 PMPY (95% CI 1471-2209), which is comparable to that observed when original case definition is used. The adjusted net incremental expenditure of probable IBS cases in North Carolina was $650 (95% CI 81-1220). Although the adjusted net incremental expenditures in North Carolina were lower for probable cases than for the original IBS cohort, the patterns of expenditures for both groups were similar. However, in California, expenditures were much greater for probable IBS cases than for those fulfilling the original case definition. Annualized mean expenditure PMPY for probable IBS cases was $5934 (95% CI 5464-6404), resulting in net unadjusted and adjusted IBS-related net incremental expenditures of $3854 (95% CI 3474-4234) and $2025 (95% CI 1443-2501) PMPY, respectively. The higher PMPY expenditures for the California probable IBS cases arose largely from higher mean prescription ($1608) and physician ($1484) expenditures.


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