Purpose: VA Healthcare System is the largest US provider of care to those with HIV and benefits from one of the most highly developed electronic medical information systems in the world. Immunology Case Registry (ICR) is an automated electronic data repository designed to monitor the costs and quality of HIV care. Decision Support Systems (DSS) was developed separately to monitor utilization and costs on all veterans in care. Because these systems use different methods for collecting overlapping data, they provide an opportunity to compare the accuracy and completeness of each repository. Methods: We compared data collected in DSS and ICR for 22,647 HIV+ veterans with an in or outpatient visit in FY 2002 for nine laboratory tests (Table 1). For each test, out of all individuals with a lab from either source, we calculated the percent of individuals with a result from each source. For individuals with results in both repositories, we calculated Pearson's correlation coefficients to quantify the correlation between overlapping lab values. Results: For six of the nine laboratory tests, DSS provided laboratory values on more individuals. ICR provided laboratory values on slightly more individuals for alanine aminotransferase and on substantially more individuals for HIVRNA viral load (VL) and CD4 (Table 1). Overlapping results were nearly perfectly correlated with the exception of CD4. Conclusions:  Despite drawing data from the same electronic record system, ICR and DSS each miss individuals with lab results in the other repository. This is likely due to discrepancies in the downloading process. The result of performance measures that count the number of CD4 tests done within a year or the proportion of patients achieving undetectable viral load may depend upon the repository used. Validation of data repositories should be mandatory before they are used to measure healthcare quality.

Table 1. Summary of Lab Values                                    

	# Individuals with Value from DSS or ICR	% with Value from DSS	% with Value from ICR	Correlation Coefficient for Overlapping Values
Hemoglobin	19,848	91	87	.997
Aspartate Aminotransferase	18,985	99	86	.997
Alanine Aminotransferase	19,725	86	88	.999
Glycosylated Hemoglobin	4,008	95	80	.991
Creatinine	19,470	92	86	.990
White Blood Count	19,901	91	87	.961
Glucose	19,535	96	85	.940
HIVRNA VL	16,654	63	98	.989
CD4	16,381	64	98	.875