The antinuclear antibody (ANA) test is positive in almost all ...

[jazziefee]

The antinuclear antibody (ANA) test is positive in almost all people who have systemic lupus erythematosus (SLE). It is also positive in some patients who do not have SLE.
 
  The anti-deoxyribonucleic acid (DNA) test is positive only in people with SLE but not in all who do. Which of the following is true?
 
  a. The ANA test is a good screening test, and anti-DNA test is a good confirmatory test.
  b. The anti-DNA test is a good screening test, and the ANA test is a good confirmatory test.
  c. Both are good screening tests for SLE.
  d. Neither of these tests is valid.

Question 2

A purchased hemoglobin standard is used to adjust a hemoglobinometer. This standard is being used as a:
 
  a. Control
  b. Precision check
  c. Delta check
  d. Calibrator

[alvinum]

Answer to Question 1

ANS: A
Because almost all patients with SLE have a positive ANA test, it is a good screening tests (if the result is negative, then it practically rules out this diagnosis for a patient). However, because it is also positive in other patients, the anti-DNA test is a good confirmatory test, because only patients with SLE have a positive result. In practice, the ANA test is done first; if it is positive, then the anti-DNA test is done as follow-up. If a patient is positive with both tests, then his or her diagnosis is SLE.

Answer to Question 2

ANS: D
Standards are used to calibrate instruments. Controls are used to routinely evaluate the accuracy of a method once it is calibrated. Precision is a measure of reproducibility, whereas delta checks compare a patient result with a previous result (same test on the same patient). This can only be done for a test result that essentially does not vary significantly from testing time to testing time.

[jazziefee]

Excellent

[Jossy]

TYSM