Data
This retrospective analysis of linked cancer registry and Medicare claims data included men at least 66 years of age diagnosed with incident PCa between 2005 and 2007 as listed in the SEER cancer registry. Cases were limited to those diagnosed with stage IV metastatic (M1) disease as identified by the American Joint Committee on Cancer Tumor-Node-Metastasis (AJCC-TNM) stage, 6th edition [14]. Claims data from 2004 to 2009 were extracted from linked Medicare claims files. The requirement for continuous enrollment in Medicare Parts A and B during the 12 months prior to and including the month of diagnosis constituted an additional inclusion criterion. Exclusion criteria were: 1) health maintenance organization (HMO) enrollment during the 12 months prior to and including the month of diagnosis since HMO claims can be unreliable due to missing data; 2) history of other cancers within 5 years prior to PCa diagnosis. Patients were censored if they enrolled in an HMO or lost Part A and/or B enrollment at any time following the diagnosis date, or if the end of the study period (December, 2009) was reached. This study was approved by the University of Maryland Baltimore Institutional Review Board (#HP-00049426).
Variables
Measures of bone metastasis diagnosis or associated health utilization
Patients were identified as having a SEER-based measure of BM if the AJCC metastatic component in the Collaborative Stage (CS) coding system indicated ‘M1b’ status, i.e. metastasis to bone at diagnosis. In defining the study cohort, we excluded the first year (i.e. 2004) in which the M1b measure became available in order to avoid possible coding problems that could have arisen as cancer registries gained familiarity with furnishing the M1b code. We investigated differences between three claims-based approaches to identify patients with BM-related claims (see Figure 1). We created a ‘generous’ approach (Approach 1), adopted an approach that is similar to the approach used in previous studies [6, 7] (Approach 2), and created a more restrictive approach (Approach 3) as follows:
Approach 1
At least one inpatient, outpatient, or carrier claim with an ICD-9 diagnosis code of 198.5 (‘secondary malignant neoplasm of bone and bone marrow’) in any diagnosis field.
Approach 2
At least one inpatient claim with an ICD-9 diagnosis code of 198.5 as the primary or secondary discharge diagnosis; OR at least one outpatient claim with a diagnosis code of 198.5 paired with a code for procedures used to diagnose or treat BM such as bone scan, bone biopsy, and/or use of intravenous bisphosphonate; OR at least one outpatient physician claim with a diagnosis code of 198.5.
Approach 3
At least one inpatient claim with an ICD-9 diagnosis code of 198.5 in any diagnosis field; OR at least two outpatient claims within a 90-day window with a diagnosis code of 198.5.
For each of the three approaches, patients were classified as having concurrent BM-related claims if claims submitted in the month before, during, or after the month of PCa diagnosis satisfied the condition stipulated by the approach. The exact date of diagnosis is not available from the SEER data and Medicare claims relevant to an event occurring in a particular month can appear in the month prior to and following the month in which the event occurred [15]. Figure 2 provides a graphical representation of ‘concurrent BM’-related claims, i.e. BM-related claims that were considered to be concurrent with the PCa diagnosis. The 3-month (90-day) window has been used in previous studies to define concurrent BM [6].
Demographics and health care utilization measures
Patient-level demographic and clinical variables obtained from the SEER files include age, race, marital status, urban residence, prostate specific antigen (PSA) level and tumor differentiation at diagnosis. We assessed comorbid illness using the Charlson Comorbidity Index (CCI) [16] and the National Cancer Institute (NCI) Combined Index [17] using claims from the 12-month period before the month of diagnosis. Treatment receipt, use of health services such as bone biopsy, and bone or joint imaging, PSA tests, and cancer specialist visits were identified from MEDPAR and Part B claims.
Statistical analysis
Cross-tabulations of the claims-based BM approaches and the SEER-based measure of BM were used to compare concordance. We calculated sensitivity, specificity, and positive predictive value (PPV) for each approach compared to the M1b measure from SEER. Sensitivity for each claims-based approach was calculated as the proportion of patients with a SEER-based BM diagnosis who were identified to have BM-related utilization in Medicare claims. Specificity for each claims-based approach was calculated as the proportion of patients without a SEER-based BM diagnosis who also did not have BM-related utilization in Medicare claims. Positive predictive value was calculated as the proportion of patients with claims-based BM-related utilization who had incident BM diagnosis based on registry data.
In order to investigate the possibilities for improving sensitivity, we selected the measure with the lowest sensitivity for use in subsequent analyses. The chi-square test identified statistically significant differences in health services utilization between patients grouped with respect to: (1) presence or absence of concurrent BM-related health services utilization according to the claims-based approach; and (2) presence or absence of BM at diagnosis according to the SEER-based measure of BM.
To identify additional measures that could enhance the sensitivity of claims-based approaches, the sample with SEER-based evidence of BM was stratified by the presence or absence of concurrent BM according to claims-based Approach 3. Among this sample of patients with a diagnosis of BM based on registry data, the objective was to identify health resource utilization categories that are commonly reported among patients without BM-related claims. Utilization categories meeting these criteria can be used to improve the sensitivity of definitions created to identify men with an incident diagnosis of BM and/or with a diagnosis of BM outside the diagnosis window using health care claims data. We conducted sensitivity analysis focused on improving the sensitivity of Approach 3.