CLINICAL LAB SCIENEC

CHAPTER 10: QUALITY ASSURANCE 253
will produce poor results. In addition, postanalytical clerical errors are the most
common type of errors that occur, even when the equipment and supplies are in
good order. In the experience of most medical laboratory personnel, the majority
of clerical difficulties are associated with patients who have the same last name,
unless bar code identification bands are correctly used. But there have been some
reports of bar codes being erroneously read by the computer scanner.
Before the widespread use of computerized reports and bar codes affixed
to samples at the time of collection, there were many more errors than are seen
today. Examples of errors from pre-computer days were:
• Displaced decimal point mistakes
• Patients who moved from one room to another
• Transfer of results to the wrong person’s laboratory report form
• Direction of a patient’s report to another patient’s medical records
Many of these errors have been greatly minimized through the use of identifying
bar codes affixed to both specimen and laboratory request or drawing list,
eliminating misreading errors that may occur when the name of the patient is
written manually. The physician who receives unexpected laboratory results (or
sometimes even the degree of abnormality of results) should interpret the result
in the context of the clinical picture. He or she should ask for a repeat test if
a single result in a battery of tests is abnormal, and neither the clinical picture,
medical condition, or the other values support the unexpected result. This should
not be interpreted as meaning that unexpected test values should be ignored. But
when there is doubt as to the validity of the results, the values for laboratory
tests should be verified, and if no errors affecting the laboratory test results are
uncovered, a more extensive workup or therapeutic action may be warranted.
When an astute technician or technologist conscientiously reviews a report
and has doubts about questionable results, the procedure should always be
repeated before results reach the physician. If possible, the repeat test should
be performed on the original specimen or, if that is no longer available, a new
specimen should be obtained and tested without delay. The greater the time lapse
between the original and the new specimen, the more difficulties will be encountered
in differentiating an error in the original specimen from a true change
that may have occurred since collecting the initial specimen. One of the most
frustrating issues a laboratory director is forced to face is when a question or
complaint about a laboratory test result is presented several days or even weeks
after the test was performed. Specimens may have been discarded and the patient
may no longer be available for a routine re-collection. Then it is usually too
late for a complete investigation of the problem. Sometimes it requires voluminous
research and additional work, because an entire group of other patients
may have also shown erroneous results that were accepted by the physician and
therapy initiated on the basis of erroneous results.
Normal Reference Ranges
The most important single aspect of laboratory test interpretation is the concept
of a normal range, where test values that fall inside the range are considered
normal and those occurring outside the range are considered abnormal. The
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