tion is possible as illness may be detected as early in the disease course as possible in an effort to try and prevent the disease worsening and causing significant complications. Ideally there should be a screening test for children with arthritis or other positive rheumatic physical findings with a high specificity (test normal when someone does not have the disease) and high sensitivity (test abnormal when someone has the illness). A screening test should allow early diagnosis compatible with primary or secondary prevention.
For children with arthritis, only a few diagnostic tests are available (e.g., Lyme titer) and the ANA in particular has very limited usefulness as a diagnostic test. To put it another way, ideally a test should always be positive in those with a disease, and always negative in those without a disease. This situation rarely if ever occurs, but to be useful a test generally needs to have sensitivity and specificity of at least 90%. That is, at least 9 out of 10 individuals with the disease will have a positive test, a "true positive", and 9 out of 10 individuals without the disease will have a negative test. Unfortunately the ANA test, whether performed by IF or by an enzyme linked immunosorbent method (ELISA), fails to demonstrate these test characteristics . The ELISA particularly has its problem with false positives.
Part of the problem is that the test is being used indiscriminately as part of "a rheumatologic work-up" or "rheumatology panel". No test can sensibly be expected to be accurate in the diagnoses of diseases as different as juvenile idiopathic arthritis (JIA), rheumatoid arthritis, SLE, MCTD, scleroderma, or the vasculitis diseases. Yet, in practice, this is what often seems to be asked of the ANA test. However, even if the test is used more sensibly to address specific questions such as: "does this child with a rash and fever have lupus?" or "does this child with a swollen knee have juvenile idiopathic arthritis (JIA)?", or "is this child with JIA going to develop uveitis?" we would argue that the ANA test is simply not accurate enough to answer even these questions.
ANA in healthy populations
A number of studies have looked at the frequency of positive ANA tests in "healthy" individuals. A study by Arroyave et al. in 1988  screened sera from 241 "normal" children, testing for only IgG ANA, using both mouse kidney and human epithelial cells (HEp-2 cells). The study found a maximum positivity rate of only 2.0% at the lowest dilutions. However, data from adult studies have found much higher rates. In an adult study from 15 international laboratories using HEp-2 cells as substrate , ANA positive tests occurred in 31.7% of a putatively normal population at a serum dilution of 1:40. Even at a dilution of 1:320, 3.3% of the sera were positive. Interestingly the ANA frequency did not differ significantly across the age range of 20-60 years. The rate of ANA positivity among blood donors in Holland was also quite high at 12.7%, with titers greater than 1:80 occurring in over 4% . It is not clear why there is such a low frequency of ANA positivity in children, compared to the much higher frequency found in most adult studies (of which only two of many are referenced here). As ANA tests are usually performed on children or adults with musculoskeletal or rheumatologic symptoms or signs, the frequency of ANA among clinic populations is more pertinent to our discussion than the situation in the normal population
ANA in clinic populations-ANA titers
Chudwin et al. in 1983  evaluated the clinical and laboratory findings in 138 children with a positive ANA test. The authors interpreted the fact that two-thirds of the patients had a specific connective tissue disease as being indicative that the ANA test is useful. Yet the fact that one third did not have a definitive inflammatory disease indicates that the ANA test has a very high false positivity rate.
We evaluated the results of all the ANA tests performed at British Columbia's Children's Hospital over a 5 year span . We found that the ANA test was