CLINICAL LAB SCIENEC

248
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
Critical Reminder
When a Run Should Be Rejected
1. When one control exceeds the
established mean by ±3 SDs
2. When one control exceeds the
mean by 2 SDs in the same
direction (±) for two consecutive
times or on two controls in the
same run
3. When two controls in the same
run have a difference between
the established values by 4 SDs
(i.e., one control is +2 SDs and the
other is –2 SDs)
4. When four consecutive controls
exceed the mean by 1 SD or more
in the same direction (on the same
side of the mean value; this is
called a shift)
5. When 10 consecutive values fall
on the same side of the mean
Sequential Steps for Out-of-Range Controls
1. Repeat the test procedures using the same control or calibrator material
(standard).
2. Repeat the procedure(s) with a new vial of control or calibrator material.
3. Insure all reagent lot numbers match the assay sheets in place and that expiration
dates have not been reached.
4. Look for variations in results such as shifts or trends, or obvious instrument
malfunctions.
5. If a new batch of control or calibrator material (standard) is available, repeat
the testing using the new lot.
6. Routinely perform the basic preventive maintenance for each instrument on
a regular basis, but repeating this process when an error is discovered often
uncovers a problem that just occurred.
7. Recalibrate the instrument if required before performing repeat testing of
the control material.
8. Open new test reagents and calibrate the instrument before performing
repeat testing if required.
9. Call for service from the manufacturer’s technical service department.
10. Notify the immediate section supervisor, who may contact the laboratory
manager.
11. Thoroughly document corrective action taken as laboratory inspectors will
investigate this area.
In summary, a “quality” QC program ensures that steps and
documentation have been taken when results do not meet the
guidelines for the QC program. This ultimately proves that the
laboratory is reporting accurate and reliable patient test results.
Remember, control results may be above or below the target
value. In either case, the results are equally in error and must be
evaluated in the same manner.
Reject the Test Run and Do Not Report Patient Results
The accompanging Critical Reminder states five shortened versions
of Westgard rules for rejecting the run (batch of specimens)
for a laboratory procedure.
Comparison of Precision
It is sometimes necessary to perform certain statistical processes
when two versions of a laboratory procedure are being
compared. Obviously, it would be important to determine
which method would be most accurate. The t-test is a procedure
in which two versions of a single test such as a glucose
determinations, are being compared. If the results are the same
(null hypothesis), factors other than accuracy would be used to
determine the method to choose. Another test, the F-test, is used
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