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Public Health Dispatch: Adverse Events and Deaths
Associated With Laboratory Errors at a Hospital ---
Pennsylvania, 2001
On August 3, CDC was contacted by the Pennsylvania Department of
Health (PADOH) to assist with an investigation of laboratory errors that may have
contributed to the deaths of two persons taking the anticoagulant drug warfarin
(Coumadin®*) (DuPont Pharmaceuticals Company, Wilmington, Delaware). The Food and
Drug Administration (FDA) also is conducting an investigation of these incidents.
Warfarin inhibits blood clotting and is prescribed for the management and prevention
of conditions such as strokes, clots in the veins, and heart attacks. Physicians
routinely monitor warfarin's anticoagulation effect on the blood by following two
laboratory results: the prothrombin time (PT) and the International Normalized Ratio (INR).
The INR is a numeric value calculated from the PT; the World Health
Organization recommends the INR to standardize PT results from various manufacturers'
devices and testing reagents (1). Physicians use INR to compare test results performed
at different laboratories.
During June 4--July 25, a hospital laboratory in Pennsylvania reported 2146
tests with correct PT results but with incorrectly calculated INR results. The
mathematical formula required to calculate the INR uses a reagent-specific number, the
International Sensitivity Index (ISI). In June, the hospital laboratory did not verify the new
reagent used in the PT measurement device; as a result, the ISI used to calculate INR
was incorrect for the reagent used. For approximately 7 weeks, the reported INRs
were falsely low. Some physicians who received these reports increased their
patients' doses of warfarin. In addition to investigations into the two deaths, efforts are
under way by PADOH Bureau of Laboratories, Centers for Medicare and Medicaid
Services (CMS), and CDC to identify other patient morbidity and mortality associated with
the error, its possible causes, and the steps needed to prevent its recurrence. FDA
is reviewing possible deficiencies in the manufacturer's reagent package labeling.
To avoid the combination of events preceding the errors in
Pennsylvania, laboratories reporting PT and INR should review the reagent package
insert information or consult the reagent manufacturer to verify that the correct ISI for
both the instrument and the particular lot of reagent being used is identified and
applied correctly to the calculation of the INR. Laboratories should provide and
physicians should consider using both the PT and the INR when contemplating a change in
a patient's warfarin dose. Warfarin is one of the most common drugs associated
with medication errors, and appropriate warfarin use has been identified as an
important
indicator of high-quality health care and patient safety
(2,3). Incorrect laboratory reporting of INR results further contributes to the risk for complications of
warfarin use.
The Safe Medical Devices Act of 1990 requires hospitals and other patient
facilities to report to FDA deaths and serious injuries associated with the use of
medical devices, including clinical laboratory assays and equipment. FDA also
encourages health-care providers to voluntarily report through MedWatch product problems
or concerns related to medical devices. Confidentiality of voluntary reporters
is maintained on request. Information about FDA's mandatory and voluntary
adverse event reporting programs is available at
<http://www.fda.gov/medwatch>
or by telephoning (800) 332-1088. To monitor and prevent adverse patient events
and medical errors, CDC, the Agency for Healthcare Research and Quality, CMS, and
FDA are participating in the Patient Safety Task Force, a federal initiative to reduce
the occurrence of injuries that result from medical errors. Information is available at
<http://www.ahrq.gov/qual/taskforce/psfactst.htm>.Additional information on CDC's efforts to monitor and prevent adverse patient events and medical errors is available from
CDC, telephone, (404) 498-1250.
Reported by: Office of the Director, Div of Healthcare Quality Promotion, National Center
for Infectious Diseases, CDC.
References
Riley RS, Rowe D, Fisher LM. Clinical utilization of the international normalized
ratio (INR). J Clin Lab Anal 2000;14:101--14.
Summary of 1999 information submitted to MedMARx: a national database for
hospital medication error reporting. Rockville, Maryland: U.S. Pharmacopeia, 2000. Available
at <https://www.medmarx.com/medmarx>. Accessed August 2001.
Jencks SF, Cuerdon T, Burwen DR, et al. Quality of medical care delivered to
Medicare beneficiaries: a profile at state and national levels. JAMA 2000;284:1670--6.
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these organizations or their programs by CDC or the U.S. Department of Health and
Human Services. CDC is not responsible for the content of pages found at these sites.
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