Table 1.

Statistical terms relevant for ANA testing.

Statistical measure	General explanation	Implication for ANA
Sensitivity	Statistical measure of how accurately a test correctly identifies diseased individuals	ANA is used as screening test. High sensitivity is important. The sensitivity for different AARD varies (i.e., higher in systemic lupus erythematosus versus myositis)
Specificity	Statistical measure of how well a test correctly identifies absence of the disease in question	Importance of specificity depends on pretest probability. In settings with low pretest probability, high specificity is required.
Diagnostic efficiency	Combination of sensitivity and specificity	Not commonly used
False negative (clinically)	Negative test result of a diseased individual	ANA is used as screening test. False negative results are undesirable. However, in all AARD, patients without a positive ANA test exist. Therefore, a negative result should never be used to rule out AARD.
False positive (clinically)	Positive test result of an individual without the disease in question	In case of low pretest probability, false positive results significantly impact the posttest probability
False negative (analytically)	Negative test result in the presence of the respective analyte	See negative positive (clinically)
False positive (analytically)	Positive test result in the absence of the respective analyte	See false positive (clinically)
Positive predictive value	Ratio of true positive to combined true and false positives.	Depends on the prevalence (pretest probability)
Negative predictive value	Ratio of true negatives to combined true and false negatives.	Depends on the prevalence (pretest probability)
Positive likelihood ratio	The probability of a positive test results in patients with the disease divided by the probability of a positive test result in individuals without the disease. Independent from prevalence.	#Important information for clinicians. Should be included in the laboratory report together with an explanation of its significance in the context of the test result.
Negative likelihood ratio	The probability of a negative test result in patients with the disease divided by the probability of a negative test result in individuals without the disease. Independent from prevalence.	#Important information for clinicians. Should be included in the laboratory report together with an explanation of its significance in the context of the test result.

  ^#The importance of the likelihood ratio in the laboratory report is controversially discussed, but might improve use of ANA test results in the future.