Patient Safety Tip of the Week
November 25, 2014
Misdiagnosis Due to Lab Error
We’ve done lots of columns on serious test results falling
through the cracks and leading to delays in diagnosis. Sometimes, however,
patients may be given an incorrect diagnosis based on specimen mixups or other issues related to lab specimens.
A recent case in Ontario, Canada illustrates the latter (Carville
2014a). A 46 y.o. man with a chronic cough had a
CT scan that suggested sarcoidosis. However, he underwent lung biopsy that was
interpreted as showing Stage 4 lung cancer. Chemotherapy was recommended and he
was under the impression he had less than 12 months to live, a prognosis
tearfully relayed to his wife and young children. But the patient did not feel
like he was dying and sought further opinions. He declined chemotherapy while
undergoing those outside evaluations. Several outside consultants felt he did
not have cancer and ultimately a second biopsy showed no sign of cancer and he
was diagnosed as having sarcoidosis.
The hospital where the original biopsy was done subsequently
reanalyzed the specimen and concluded it was cross-contaminated with that of
another patient who did have advanced lung cancer (Carville
2014b). DNA analysis apparently showed three specimen fragments on the
slide, 2 from the patient and one from the other patient (whose specimen
apparently was processed on the same day).
You’ll recall from our prior columns that 2 patients are
typically impacted by specimen mixups (eg. one may be erroneously given a cancer diagnosis and the
other erroneously told he/she does not have cancer). However, in the current
case the other patient had been given a correct diagnosis and was not impacted
by the lab issue.
A physician executive was quoted as saying this was a “one
in a million kind of occurrence” (Carville
2014b). But is that really true? In our January 22, 2013 Patient Safety Tip
of the Week “You
Don’t Know What You Don’t Know” we discussed occult specimen
provenance complications (SPC’s).
It’s a scary concept because it is occult,
i.e. the error is not recognized because it is not identified by standard
laboratory procedures. There are actually 2 types of such errors:
- Type 1 complete
transposition between patients
- Type 2 contamination of a
patient’s tissue with that of one or more other patients
So I could have a prostate biopsy that either gets mixed up
with someone else’s biopsy or that gets contaminated by tissue from another
patient and my specimen gets reported as showing cancer. I might end up getting
a treatment for prostate cancer and all the side effects even though I don’t
have cancer. Or I actually could have cancer and my specimen gets interpreted
as normal and I don’t get any treatment. Such errors usually only come to
attention when a patient undergoes, for example, a mastectomy or prostatectomy
after a biopsy was interpreted as showing cancer and the full surgical specimen
removed shows no cancer.
In that column we noted a study providing an estimate of how
often such SPC’s occur (Pfeifer 2013).
The authors examined about 13,000 prostate biopsy specimens from a wide variety
of urology practices and pathology laboratories using a DNA identification
technology. They found the frequency of occult type 1 errors (a complete
transposition between patients) was 0.26% and type 2 errors (contamination of
the patient’s tissue with 1 or more unrelated patients) was 0.67%. Overall, the
mean frequency of SPCs across practice settings was 0.22% for type 1 errors and
1.69% for type 2 errors.
Basically, it means that just under 1% of patients might be
given an incorrect diagnosis that no one even suspects is incorrect!
Perhaps just as striking is the fact that virtually every
lab or clinical setting they studied had at least one SPC identified. So it’s
not simply that one lab is making errors. Rather this is a problem that can and
does occur in every lab.
In one of our earliest columns on lab errors (see our
October 9, 2007 Patient Safety Tip of the Week “Errors
in the Laboratory“) we noted
a paper (Suba
2007) that suggested we consider the “DNA
timeout” akin to the surgical timeout where we ask the question “Is this
the correct diagnosis for the correct patient?” before doing an invasive
procedure. Particularly when all the pieces of evidence do not completely mesh
that may not be a bad idea.
Unlike the process improvements and technological solutions
to prevent specimen mixups noted in our prior
columns, we know of no current means of otherwise identifying such cross-contamination.
Therefore, the astute clinician must always be thinking “is this the correct
diagnosis for this patient?” particularly before embarking on an invasive
procedure or recommending treatment with potentially severe side effects.
The current case thus also has lessons learned about diagnostic error. The patient
apparently was angered that a physician and nurse walked out of a meeting with
him when he challenged the diagnosis of cancer (Carville
2014b). Not only did the patient feel relatively healthy for someone said
to have advanced cancer but he also had not lost any weight even 6 months after
the original diagnosis of advanced cancer. In our many prior columns on diagnostic
error (see the full list below) we’ve discussed some of the cognitive biases
that may have been in play here: anchoring,
early closure, and confirmation bias (actually its
corollary: ignoring disconfirming evidence).
Fortunately in the current case there was a happy ending and
the patient never underwent unnecessary chemotherapy. Nevertheless, he and his
family undoubtedly suffered unimaginable stress during the ordeal. Let’s hope
everyone can learn from this case and recognize the problematic scenario early.
Some of our other
columns on errors related to laboratory studies:
- October
9, 2007 “Errors
in the Laboratory“
- November
16, 2010 “Lost
Lab Specimens”
- October
11, 2011 “LEAN
in the Lab”
- March 6, 2012 ““Lab”
Error”
- April
2012 “Specimen
Labeling Errors”
- January 22, 2013 “You
Don’t Know What You Don’t Know”
- April 15, 2014 “Specimen
Identification Mixups”
Some of our prior
columns on diagnostic error:
- September 28, 2010 “Diagnostic
Error”
- November 29, 2011 “More
on Diagnostic Error”
- May 15, 2012 “Diagnostic
Error Chapter 3”
- May 29, 2008 “If
You Do RCA’s or Design Healthcare Processes…Read Gary Klein’s Work”
- August 12, 2008 “Jerome
Groopman’s “How Doctors Think”
- August 10, 2010 “It’s
Not Always About The Evidence”
- January 24, 2012 “Patient
Safety in Ambulatory Care”
- October 9, 2012 “Call
for Focus on Diagnostic Errors”
- March 2013 “Diagnostic
Error in Primary Care”
- May 2013 “Scope
and Consequences of Diagnostic Errors”
- August 2013 “Clinical
Intuition”
- January 2014 “Trigger
Tools to Prevent Diagnostic Delays”
- January 14, 2014 “Diagnostic
Error: Salient Distracting Features”
- May 2014 “Frequency
of Diagnostic Errors in Outpatients”
- June 24, 2014 “Lessons
from the General Motors Recall Analysis”
- And our review of Malcolm
Gladwell’s “Blink” in our Patient Safety Library
References:
Carville O. Hamilton father misdiagnosed with lung cancer
demands answers. Thestar.com (Hamilton, Ontario) Published on Fri Nov 14 2014
Carville O. Hospitals ‘deeply sorry’ for lung cancer
misdiagnosis. Thestar.com (Hamilton, Ontario) Published on Fri Nov 14 2014
Pfeifer JD, Liu J. Rate of Occult Specimen Provenance
Complications in Routine Clinical Practice. Am J Clin Path 2013; 139: 93-100
http://ajcp.ascpjournals.org/content/139/1/93.abstract
Suba EJ, Pfeifer JD, Raab SS.
Patient Identification Error Among Prostate Needle Core Biopsy Specimens—Are We
Ready for a DNA Time-Out? J Urol 2007; 178(4):
1245-1248
http://www.jurology.com/article/S0022-5347%2807%2901423-1/abstract
Print “PDF
version”
http://www.patientsafetysolutions.com/