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Letters to the Editor |
Department of Pathology and Laboratory Medicine Tan Tock Seng Hospital Singapore 308433 Fax 65-62536507 E-mail Robert_Hawkins{at}ttsh.com.sg
To the Editor:
Information technology provides data that are useful for assessing potentially unnecessary repeat laboratory testing (1)(2). Rather than using these data to directly measure the appropriateness of laboratory testing, we identified an outcome that we believe is indicative of inappropriate testing the majority of times. This useful surrogate measure of potentially inappropriate test use within and between departments and institutions can help to standardize discussion of this problem. We extended the approach of Weydert et al. (3), who calculated an index of test overuse by counting inpatients with serum sodium results within reference intervals on 
4 consecutive days over a 1-month period and presented the monthly volume of tests ordered on these patients as a proportion of the total sodium testing workload.
At Tan Tock Seng Hospital, a 1200-bed acute-care hospital in central Singapore, we examined repeat testing on inpatients for the top 14 analytes by volume and repeat testing rates in the different clinical departments over a 1-year period. All 2002 records for the top 14 analytes by inpatient volume [potassium, sodium, creatinine, glucose, urea, alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotransferase (AST), chloride, bicarbonate, albumin, bilirubin, total protein, and 
-glutamyltransferase (GGT)] were extracted from the laboratory information system into Microsoft Access, after which individual sample records were processed with Visual Basic for Applications (VBA) Access to determine repeat samples and the time differences between sequential samples. A single piece of VBA Access code retrieved the distinct patient identifiers from the data table and then looped through the individual samples in ascending order by sample date/time for each distinct patient identifier. With each iteration, the loop-counter value increased by 1 and was written to the sequence number field. If the sequence number was 1, then the time difference was set to null; otherwise the time difference was calculated as the difference between the present sample date/time and a date variable, PreviousSampleDateTime. After this "IF" statement, PreviousSampleDateTime was replaced by the present date/time, and the loop was restarted. We used 2 different definitions of potentially inappropriate repeat testing, both with intersample time intervals of <26 h (for sodium, potassium, urea, creatinine, chloride, bicarbonate, and glucose) or <50 h (for AST, ALT, GGT, ALP, bilirubin, total protein, and albumin) chosen to approximate daily or QOD (every second day) requesting with an added 2 h to avoid missing repeats falling strictly outside a 24-h interval. Definition A, which required 4 or more sequential samples with results all within the reference interval, was similar to that used by Weydert et al. (3), whereas definition B differed by considering sequences of 3 or more and counting only the third and subsequent samples as potentially inappropriate (vs all samples on that patient; Table 1
).
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The tests we analyzed represented 73.7% of the total biochemistry inpatient workload. Overall, 58% of all measurements were repeat tests. The cumulative potentially inappropriate repeat rates according to definitions A and B for the top 7 tests were 2.2% and 1.9%, respectively, of the entire annual inpatient biochemistry workload and for the top 14 tests were 2.3% and 2.1%, respectively. The top 6 department A and B rates were as follows: neurointensive care, 32.1% and 25%; surgical intensive care, 31.2% and 24.1%; medical intensive care, 14.1% and 11.8%; ear, nose, and throat, 8.3% and 6.9%; neurosurgery, 6.1% and 5.4%; and coronary care, 3.5% and 3.8%. When ranking was by volume of potentially inappropriate tests, the ear, nose, and throat department was replaced by general surgery and coronary care was replaced by general medicine. General medicine was the largest discipline by total test volume, but it had potentially inappropriate repeat rates of only 0.8% and 1.0%. The overall A and B rates were 26.4% and 20.8% for the 3 intensive care units and 3.6% and 3.2% for the top 14 departments.
Reported rates of potentially inappropriate test ordering range from 20% (4) to 95%(1), reflecting poor agreement between assessors (5) and different views from different auditing groups (6)(7), as well as differences in the definition of potentially inappropriate testing, which has been reported even in critical care units, where electrolyte measurements may be ordered excessively (8). Although "potentially inappropriate" repeat testing as defined here may actually be appropriate in some settings, our method is useful for identifying potential overuse at macrodepartmental and institutional levels.
Potentially inappropriate repeat testing for the top 7 analytes by volume represented 2% of the total biochemistry workload at our institution, translating into an average of >70 unnecessary measurements per day. Tests for only a few analytes make up the majority of this workload and also have the highest repeat test proportions, the highest potentially inappropriate repeat rates, and the longest unbroken sequences of potentially inappropriate repeat tests. These results suggest that methods to reduce overrequesting of tests, such as computerized clinician ordering systems (9)(10), need not be comprehensive but can target a few key tests and departments.
References
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