Quality control, delta checks, and predictive value

Question 1

What is a QC?

Answer 1

QC is a statistical tool that is used to assure the reliability of patient test results. Statistical quality control practices are critical for assuring patient test results.

Question 2

What is the acceptable range for the QC?

Answer 2

Mean +/- 2SD = 95% cl. The value of the quality control specimen is known and is represented by an “acceptable range” of values that have been statistically calculated. Values are collected until 30+ values are obtained.

Question 3

What does a QC do?

Answer 3

It statistically validates the accuracy of analytical run. (analytical run = methodology, testing procedure, reagents, entire test system, instruments)

Question 4

What QC not do?

Answer 4

cannot determine if the sample submitted is from the correct patient

Question 5

How is QC used?

Answer 5

QC samples are anayzled along with patient samples, If they are within acceptable limits, then the analytical run is validated as accurate. this means the patient results are valid and can be reported.

Question 6

What happens if the QC results are not within acceptable limits then…

Answer 6

then the analytical run is not valid. This indicates an analytical error has occurred that jeopardizes the patient results, and patient results cannot be reported out.

Question 7

define accuracy:

Answer 7

refers to the closeness of a measurement to the true value

Question 8

define precision:

Answer 8

refers to the reproducibility of a measurement

Question 9

define reliability:

Answer 9

refers to the accuracy and precision of a measurement

Question 10

What is the reference range:

Answer 10

range of values the majority of patients (95%) of healthy individuals will have. outside of the range is usually indicative of having a disease.

Question 11

What is a critical value?

Answer 11

a test result that indicates the patient requires immediate medical intervention. If immediate medical intervention is not received, patient may die.

Question 12

What is a qualitative assay?

Answer 12

positive or negative results, reactive or non reactive results, growth or no growth.

Question 13

What is a delta check?

Answer 13

another tool used by the lab to assure accurate patient test results. the most recent test result for a particular patient is compared to the most previous test result for that patient.

Question 14

What is a delta check failure?

Answer 14

if the test result has changed significantly from the last time the test was done, a delta check failure occurs. The delta check failure means the change in test results was not physically possible.

Question 15

Who is responsible for finding the cause of the delta check?

Answer 15

the technologist

Question 16

what do we want screening tests to have?

Answer 16

high sensitivity, not very man false negatives. high negative predicative value. so patients with disease will not be missed.

Question 17

what do we want confirmatory tests to have?

Answer 17

high specificity. high positive predictive value. patients without the disease will be ruled out.

Question 18

if a high cutoff value is used, then the specificity of the test can reach 100%….but…

Answer 18

the sensitivity will be decreased.

Question 19

if a low cutoff value is used, then the sensitivity of the test can reach 100%….but..

Answer 19

the specificity will be decreased.