Well-Child Care Visits and Risk of Ambulatory Care–Sensitive Hospitalizations
Published Online: May 10, 2013
Jeffrey O. Tom, MD, MS; Rita Mangione-Smith, MD, MPH; David C. Grossman, MD, MPH; Cam Solomon, PhD; and Chien-Wen Tseng, MD, MPH
Children less than 5 years old have higher hospitalization rates than older children.1 Finding approaches to minimize morbidity for these children (eg, decreasing asthma exacerbations) may reduce hospitalizations. Regular attendance at well-child care (WCC) visits may prevent unnecessary hospitalizations through timely immunizations and/or chronic disease management. WCC visits likely have a higher impact for young children due to the greater frequency of recommended WCC visits in the first 3 years of life (13 visits) compared with older children (1 visit per year through age 18 years).2 Prior studies evaluating the association between WCC visit adherence and hospitalizations have been mixed, as 3 studies found that higher WCC visit adherence was associated with decreased ambulatory care–sensitive hospitalizations (ACSHs) while 2 studies found no association.3-7 Only 3 of these studies accounted for the timeliness of WCC visits.3,5,7 No study has evaluated this relationship in integrated healthcare delivery systems. Unlike other healthcare systems, integrated healthcare delivery systems have greater control in standardizing and improving the care patients receive (ie, population-based care), which can decrease practice variation.8,9 In addition, integrated healthcare delivery systems often place high importance on preventive care and therefore encourage and provide these services at no charge. Evaluating WCC visit adherence and risk of hospitalization in this setting provides a unique opportunity to understand this relationship where all patientsreceive similar WCC visit content.
The goal of this study was to understand whether parents’ timely adherence to WCC visits was associated with risk of ACSHs among young children enrolled in an integrated healthcare delivery system. ACSHs represent hospitalizations which are potentially preventable with adequate access to and/or provision of outpatient care.10 We hypothesized that poor WCC visit adherence would be associated with increased risk for ACSHs in this integrated healthcare delivery system.
Design and Setting
This was a retrospective cohort study conducted in collaboration with Group Health Cooperative, an integrated healthcare delivery system with ~640,000 members in Washington and Idaho. Claims from both the Group Health delivery system and contracted network physicians were included. This study was approved by both the Seattle Children’s Research Institute and Group Health Research Institute’s Institutional Review Boards.
We focused on children younger than 3.5 years because this age group is at higher risk for hospitalizations than older children,11 because they have higher contact rates with healthcare providers, and because Group Health encourages 1 WCC visit between the ages of 2 and 3.5 years. Children were eligible for the study if they were enrolled by 2 months of age at GroupHealth between January 1, 1999, and December 31, 2006. Participants entered the study on either January 1, 1999 (ie, already a plan member), or on their first day of enrollment during the study period. When determining a child’s complete enrollment information, we considered gaps in enrollment of <45 days as continuous enrollment based on the Healthcare Effectiveness and Data Information Set definition.12 In addition, children needed to be enrolled on or prior to a recommended WCC visit and through at least 1 of the subsequent recommended WCC visits in order to calculate adherence and minimize misclassification (Figure).
We used a previously validated list of International Classification of Disease, Ninth Revision (ICD-9) codes to identify children with chronic disease.13 Children were classified as having at least 1 chronic disease (ie, “>1 chronic disease”) if they had 1 or more claims matching an ICD-9 diagnosis included in the validated list. Children were classified as “healthy” otherwise. Since diagnosing asthma in children less than 4 years old can be challenging,14 2 or more claims for asthma (ICD-9 493.00-493.99)11 were required for a child to be classified as having asthma. The top 5 chronic disease categories for our study were: asthma (38%), congenital heart disease (15%), congenital musculoskeletal anomalies (14%), failure to thrive (7%), and hereditary and acquired hemolytic anemias (6%).
WCC Visit Adherence
A WCC visit was identified if an outpatient claim billed by a primary care provider (pediatrician, family physician, general practitioner, osteopath, or nurse practitioner) contained the standard WCC visit ICD-9 codes (eg, V20.2) in any diagnosis field. Adherence was based on Group Health’s 2000 WCC visit schedule, which was identical to the AAP’s schedule for the first 6 months and then differed from this schedule by requiring the following WCC visits through 3.5 years old: 10 months, 15 months, 2 years, 3.5 years (ie, the AAP’s 9-month, 12-month, 18-month, and 3-year visits are not required). WCC visits were included in the adherence calculation (numerator) if the WCC visit was “timely.” For example, a “4-month WCC visit” was allowed to occur on or after a child turned 4 months old and up to less than 6 months old (ie, the “4-to-6 month” WCC interval). To allow for an appropriate window of acceptability for when WCC visits might reasonably occur, we counted a “duplicate WCC visit” in 1 interval as the WCC visit for the following interval if the duplicate visit was <14 days (visits before 15 months of age) or <30 days(visits after 15 months of age) prior to the start of a WCC visit interval where no visit had occurred. Otherwise only the first WCC visit was counted for WCC visit intervals with multiple WCC visits.
WCC visit adherence (range 0% to 100%) was a timevarying variable that was updated at the end of each WCC interval. For WCC intervals that overlapped completely with a child’s study period enrollment, WCC visit adherence was calculated by dividing a child’s total number of “timely” WCC visits by the total number of recommended WCC visits from start of enrollment through the end of each age-specific WCC interval (ie, a child enrolled for “X” number of WCC visit intervals would have “X” number of WCC visit adherence values for our regression analysis). We examined WCC visit adherence using a priori categories to facilitate interpretation and comparison with our prior study as follows: 0% to 25%, 26% to 50%, 51% to 74%, and 75% to 100% (referent).
Ambulatory Care–Sensitive Hospitalizations
As defined by the Agency for Healthcare Research and Quality, a hospitalization was classified as an ACSH if the primary diagnosis was one of those included in the predetermined list of ACSH diagnoses. The only exceptions to this were for the diagnoses of dehydration or iron deficiency anemia where the ACSH diagnosis could be either primary or secondary.10 Similar to other investigators,6 we excluded “adult” conditions (chronic obstructive pulmonary disease, congestive heart failure, hypertension, pelvic inflammatory disease, skin grafts with cellulitis, and angina). We also excluded “congenital syphilis” as these hospitalizations are unlikely to be affected by WCC visits due to the fact that these infections begin in utero or at birth. Additional hospitalization diagnoses were included based on their clinical importance to children less than 3½ years old(“pneumococcal meningitis” [ICD-9 320.1], “streptococcal meningitis” [ICD-9 320.2], and “septicemia due to H. influenza” [ICD-9 038.41]). Hospitalizations prior to the age of 2 months were excluded. Children could only have 1 ACSH for analysis since we were interested in whether WCC visit adherence was associated with the time to the child’s first ACSH.
Bivariate analyses consisted of Student’s t test for comparisons of continuous variables and the Pearson’s χ2 test for categorical variables. We used a time-varying Cox proportional hazards regression model to determine the association between WCC visit adherence and time from enrollment to the first ACSH. Children were censored when they had their first ACSH, reached the end of the study (December 31, 2006), disenrolled, or turned 3.5 years old, whichever came first. Potential confounders were included a priori in multivariate analyses based on the existing literature: patient age at start of enrollment,6 gender,4,6 chronic disease (any vs none),5 and Medicaid enrollment (yes/no).11 Age at start of enrollment was modeled as a continuous variable. The reference categories were male (vs female), no chronic disease, and never on Medicaid for our categorical variables of gender, chronic disease, and Medicaid enrollment, respectively. The proportional hazard assumption was examined using STATA10. Statistical significance was determined at the P <.05 level.
We also conducted 2 sensitivity analyses. First, we used propensity scores in an attempt to control for self-selection bias (eg, children at greatest risk for ACSH may also be less likely to attend WCC visits).15,16 We predicted WCC visit adherence (categorical) propensity score probabilities with multinomial logistic regression using age at start of enrollment, chronic disease status, and whether the child was ever enrolled in Medicaid. This sensitivity analysis (data not shown) did not change our results or conclusions. Second, although we could not adjust for an appropriate measure of continuity of care for this healthcare setting (ie, “clinic level”), we adjusted for continuity of care (COC) at the “provider level” based on the importance of this potential confounder from prior studies.7,11 We used Bice and Boxerman’s COC index (range 0 to 1) to measure how often children saw the same provider.17 We analyzed COC as a time-varying categorical variable that was updated at the end of each agespecific WCC interval. The magnitude of associations and confidence intervals (CIs) were similar to our primary findings (data not shown).
Of the 23,579 children that enrolled in the health plan prior to age 2 months, 20,065 (85%) children were eligible for analyses (Figure). Nearly a quarter of our population was on Medicaid and children with >1 chronic disease accounted for approximately 11% of our study population (Table 1). Based on when children exited the study, approximately threefourths of children fell into the highest WCC visit adherence category (75-100%, Table 1). WCC visit adherence was calculated based on at least 4 recommended WCC visits for 69% of children (median 5, interquartile range: 3-6).
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