Validation of Acute Stroke in Medicare Data against WHI Kamakshi Lakshminarayan, MD, PhD presented by Dale Burwen, MD, MPH WHI Investigators Meeting May 3-4, 2012 Preliminary results; do not distribute 1

Writing Group Kamakshi Lakshminarayan Dale Burwen Joe Larson Beth Virnig Wolfgang Winkelmayer Norrina Allen Monica Safford Marian Limacher 2

Background Starting in 2010, stroke outcomes in WHI will be adjudicated in only a quarter of participants Medicare data provide potential for expanding outcome ascertainment Little is known about validity of Medicare claims for ascertaining neurologist adjudicated strokes 3

Objective Compare agreement between various algorithms to detect stroke hospitalizations in Medicare claims data and neurologist adjudicated stroke outcomes in WHI 4

Methods – Study Population Inclusions Observational study women With Medicare Parts A&B, Fee-For-Service at the time of WHI enrollment N=27,739 Those who age into Medicare Parts A&B, Fee-For-Service after enrollment until 2007 N=21138 Total N = 48,877 Exclusions Managed care at the time of their WHI enrollment Participants are censored as they enter into managed care Those with WHI adjudicated stroke outcomes prior to CMS eligibility are excluded Participants are censored 7 days after WHI stroke 5

Methods Randomly split into training & test data sets Training set N = 24,432 Test set N = 24,495 Analysis to date confined to training set 6

Stroke in WHI Rapid onset of persistent neurologic deficit attributed to obstruction or rupture of brain arterial system. Deficit is not known to be secondary to brain trauma, tumor, infection, or other cause. Deficit must last > 24 hours unless death supervenes or there is a lesion compatible with an acute stroke on CT or MRI. 7

Defining stroke in Medicare Used hospital data (MedPAR file) 8 DefinitionICD-9 codeCode Position 1. All stroke430, 431, 433.x1, 434.x1, 436, 437.1x, 437.9x Any position 2. Primary position strokeSame as abovePrimary position 3. Ischemic stroke433.x1, 434.x1, 436, 437.1x, 437.9x Any position 4. Hemorrhagic stroke430, 431Any position Results pertain to the 1 st definition

Events Included in Analysis Universe of events: –WHI confirmed strokes after neurologist adjudication –All hospitalization claims from Medicare data (stroke and non-stroke) –Goal is to classify each claim into stroke vs. not Definition of matched events: –WHI stroke & CMS stroke +/- 7 days Sensitivity analysis with wider intervals (14 days) 9

Match Results (Stroke in any diagnosis position) WHI YesWHI No CMS Yes CMS No Kappa 0.66

Reasons for Disagreement WHI Yes, CMS No (N=105) Hospital claim found +/- 7days; but claim did not have diagnosis codes meeting stroke definition No hospital claim found +/- 7 days; outpatient stroke according to WHI No hospital claim found +/- 7 days 54% (n=57) 5% (n=5) 41% (n=43) 11

Reasons for Disagreement WHI No, CMS Yes (N=374) Self-report of stroke or Transient Ischemic Attack (TIA), with hospitalization +/- 7 days –Adjudicated as TIA or carotid disease –Adjudicated as no outcome –Not adjudicated due to administrative reasons Self-report of other hospitalization No report of hospitalization – (case ascertainment of WHI) 24% (n=89) 7% (n=28) 13% (n=50) 3% (n=11) 21% (n=78) 55% (n=207) 12

Original vs. Modified Analysis WHI YesWHI No CMS Yes CMS No WHI YesWHI NoWHI No Hospitalization Reported Or Administrative denials CMS Yes CMS No Outpatient strokes5

Validation Performance Original Analysis Sensitivity: 82.0% Specificity: 99.3% PPV: 56.1% Kappa: 0.66 Modified Analysis Sensitivity: 82.7% Specificity: 99.7% PPV: 75.4% Kappa:

Validation Performance Primary Position Original Analysis Sensitivity: 73.9% Specificity: 99.6% PPV: 63.9% kappa: 0.68 Modified Analysis Sensitivity: 74.6% Specificity: 99.8% PPV: 82.3% kappa:

Discussion Initial WHI vs. Medicare agreement was moderate Key reason for a CMS event without WHI match was lack of WHI report of hospitalization –Possible reasons: Inadequate recall; disability/death and lack of proxy report Limiting analysis to CMS events that could be evaluated with WHI medical records increased PPV to 75% –Primary position diagnostic codes PPV = 82% False positives due to TIA were in a minority; mainly other diagnosis 16

Discussion (cont.) A key reason for WHI stroke without matching CMS stroke was that WHI picked up a lot of strokes coded with a variety of other diagnosis codes. –However, there was no predominant code to suggest how to modify our algorithm Another important reason was lack of CMS hospital claim within the selected time interval (+/- 7 days) –Wider time interval picked up a minority 17

Next Steps Further exploration of reasons for disagreement Test additional algorithms Consider incorporation of Medicare procedures/diagnoses for rehabilitation –To increase specificity for stroke vs. TIA, and current vs. historical stroke 18

Thank you! Questions? 19