CLINICAL LAB SCIENEC

CHAPTER 10: QUALITY ASSURANCE 245
6. This rule also detects systematic error and is applied both within and across
separate runs. It is violated within the control material when the last 10
values for the same control level are all on the same side of the mean. It is
called a shift if violated across control materials when the last 10 consecutive
values, regardless of control level, are on the same side of the mean.
The number of values considered can be decreased if three or more levels of
control are run.
7. The term Delta checks refers to the difference between a patient’s present
laboratory result and a previous result that exceeds a predefined limit.
Delta checks are done on samples from patients who have repeat analyses
of tests that have relatively stable parameters from day-to-day operations.
These parameters may be in chemistry or hematology predominantly, and
are for patients who have at least a several-day hospitalization period. Delta
checks are investigated by the laboratory internally to rule out mislabeling,
clerical error, or possible analytical error. Therefore, failures discovered by
Delta checks may be preanalytical or systematic. Actions to verify reasons
for a failure may be the repeat of the sample, repeat of the previous sample
from the same patient, or a manual method of determining the veracity of
the results. In addition, a call to the physician or nurse may confirm that a
preanalytical error occurred due to the specimen being drawn from an IV
line, mislabeling of the sample, or a drastic change in the patient’s condition.
Documentation on the patient’s report should indicate what actions were
taken and that the specimen was rerun for verification.
Quality Control for All Types of Tests
Clinical laboratories perform qualitative, semiquantitative, and quantitative
tests on a variety of biological specimens. A qualitative test is defined as one in
which a particular characteristic of the specimen is determined to be either present
or absent and is most often reported as positive or negative. Quantitative
tests determine the amount of a particular substance or property by an instrument,
with the result expressed numerically. Some tests are defined as providing
semiquantitative results. For instance, if a very small amount of protein is found
in a urine specimen, it might be reported positive as a trace amount. CLIA 88
requires that a laboratory must establish and follow an appropriate QC program
for all testing performed by the laboratory.
Establishment of Control Limits for Quantitative Tests
For quantitative methods, laboratories may use either “assayed” or “unassayed”
control materials. Assayed controls are defined as such when the manufacturer
of the materials has established the acceptable limits for the control test results.
Generally, the limits represent a 2 to 3 SD range. If the laboratory is using assayed
controls, the results obtained from testing the control material must be within
the assayed limits or range. If control results fall outside the limits, the laboratory
must take corrective action. Some laboratories will establish over time
a narrower range established by the manufacturer of 2 SDs using the assayed
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