© Copyright 2009 by the American Association for Clinical Chemistry

Patient Misidentifications Caused By Errors in Standard Bar Code Technology

M.L. Snyder, A. Carter, K. Jenkins, and C.R. Fantz

October 2010

http://www.clinchem.org/cgi/reprint/56/10/1554

© Copyright 2010 by the American Association for Clinical Chemistry

Journal ClubJournal Club

© Copyright 2009 by the American Association for Clinical Chemistry

IntroductionIntroduction

Bar code-based identification technology has improved healthcare delivery by:

Increasing speed and accuracy of identification

• Patients

• Specimens

• Blood Products

• Medication

Reducing data entry errors

• Estimated manual errors: 1 error per 300 keystrokes

• Estimated bar code errors: 1 error per 1,000,000+ scans

© Copyright 2009 by the American Association for Clinical Chemistry

Introduction (cont)Introduction (cont)

Bar codes utilize built-in data integrity checks to minimize the likelihood of erroneous scans.

Code 128, the laboratory industry standard, uses one such algorithm:

Scanner software computes a check character (CkChr) using the decoded bar code payload and compares it to a CkChr encoded in bar code (refer to supplemental Fig. 1 on the last slide of this presentation)

The decoded payload will only be accepted if the two CkChr are identical

© Copyright 2009 by the American Association for Clinical Chemistry

Introduction (cont)Introduction (cont)

However, bar code-related errors can still occur.

We identified 10 patient wristbands during the course of 1 year that generated incorrect patient identification numbers when scanned with our point-of-care glucose meters.

© Copyright 2009 by the American Association for Clinical Chemistry

QuestionsQuestions

What are potential sources of these bar code-related identification errors?

How would you test your theories?

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and MethodsMaterials and Methods

Ten defective patient wristbands were removed from service

Wristbands originated from two different thermal printer models

Wristband bar codes were either 13 x 13 mm or 25 x 12 mm (width x height)

All faulty bar codes had fine white streaks running through the bar codes

Defective bar codes were reprinted in “pristine” condition by the printer vendors for use as controls

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and Methods (cont)Materials and Methods (cont) Defective and control bar codes were each

scanned 225 times

15 scan attempts × 5 scanner models × 3 operators = 225 scans per bar code

Five bar code scanner models were tested: Two laser scanners: Roche ACCUCHEK®

glucometers (RACGs) and Metrologic MS 9540

Two CCD/LED scanners: Adesso NUSCAN 1000U and ZBA AS-8210

One omni-directional scanner: Symbol LS-9100-411

© Copyright 2009 by the American Association for Clinical Chemistry

Materials and Methods (cont)Materials and Methods (cont) Substitution and rejection error rates (%) were

determined

Substitution error: scanner generated an incorrect identifier

Rejection error: scanner failed to read (rejected) the bar code

CkChr was manually calculated for each accepted 12-digit identifier

CkChr = remainder of CkSum 103

CkSum = [105 + (XX1 × 1) + (XX2 × 2) + … + (XX6 × 6)],

XX1 through XX6 represents the first through sixth pairs of encoded bar code digits (refer to supplemental Fig. 1 on the last slide of this presentation)

© Copyright 2009 by the American Association for Clinical Chemistry

QuestionsQuestions

How might bar code substitution and rejection errors affect speed and accuracy of patient/specimen identification?

Which type of error would be expected to have more severe consequences?

© Copyright 2009 by the American Association for Clinical Chemistry

ResultsResults

Incorrectly decoded 128C identifiers produced correct CkChrs.

Some bar codes were also interpreted as non-128C bar code symbologies.

© Copyright 2009 by the American Association for Clinical Chemistry

Results (cont)Results (cont)The RACG laser scanner had the highest

substitution error ratesThe Metrologic was the only scanner without

substitution errors

© Copyright 2009 by the American Association for Clinical Chemistry

Results (cont)Results (cont)

Control bar codes reprinted in their original widths also generated substitution errors

Control bar codes printed in a suitable width for the RACG scanners (17 mm) were error free

© Copyright 2009 by the American Association for Clinical Chemistry

QuestionQuestion

Based on the differential error rates observed for the defective and different sized control bar codes, what factors do you now think likely contributed to these bar code errors?

© Copyright 2009 by the American Association for Clinical Chemistry

DiscussionDiscussion

Conclusions:

1. Worn/damaged thermal printer heads produced white streaks in the defective bar codes

2. These streaks were misinterpreted as lines/spaces in the bar codes, leading to high rates of substitution errors

3. Coincidentally, the resulting incorrect identifiers produced the correct CkChr, evading the internal 128C check system

© Copyright 2009 by the American Association for Clinical Chemistry

DiscussionDiscussion

Conclusions (cont):

4. Failure to control for bar code scanner resolution requirements also contributed to errors, as demonstrated by the substitution errors observed for the control bar codes reprinted in their original widths

5. After correcting for the resolution requirements of the scanners (17-mm-wide bar codes), no errors were observed with any of the scanners

6. Differences in scanner resolution requirements contributed to the differential error rates observed across scanners

© Copyright 2009 by the American Association for Clinical Chemistry

DiscussionDiscussion Minimizing bar code errors:

1. Print a black line under bar code to detect printer errors

2. Rotate bar code such that printer defects are observed perpendicular to the bar code lines

3. Perform preventative printer maintenance at regularly defined intervals

4. Carefully match bar code widths with resolution requirements of scanners (and vice versa)

© Copyright 2009 by the American Association for Clinical Chemistry

DiscussionDiscussion

Take-Home Message:

Bar code-related misidentifications occur more frequently than expected:

• Estimate for Code 128C: 1 in 2.7 – 37 million scans

• Our estimated error rate: 1 in 84,000 scans

Ultimately, healthcare industry should adopt more robust and higher fidelity alternatives to linear bar code symbology (2-D or matrix) to minimize this risk for patient safety.

© Copyright 2009 by the American Association for Clinical Chemistry© Copyright 2009 by the American Association for Clinical Chemistry

Supplemental DataSupplemental Data

Supplemental Figure 1. Example Code 128 C bar code. Individual components have been labeled.

Using this bar code as an example, CkSum and CkChr are calculated by:CkSum = 105 + (1 x 01) + (2 x 23) + (3 x 45) + (4 x 67) + (5 x 89) + (6 x 10) = 1060 Quotient = 1060/103 = 10Remainder (CkChr) = 30

106108967452301105 30

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