e 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 positive at a titer of 1:20 or greater in 41% of all sera tested, and in 65% of all patients in whom a diagnosis could be obtained from the ordering physician. The frequency was the same for those children with or without a diagnosis of a rheumatic disease. At a screening serum dilution of 1:40 a positive test had a sensitivity of only 63% and a positive predictive value (the frequency that a positive test is indicative of disease) of only 33% for any rheumatic disease.
For SLE, MCTD or overlap syndrome, the ANA had a very high sensitivity of 98%, but a very low positive predictive rate of only 10%. Positive and negative predictive values are affected by the prevalence of the disease being tested. Therefore one might expect somewhat better predictive values from a pediatric rheumatology clinic than from a wide population of ill children. We concluded from this study that although a negative ANA test made the diagnosis of SLE or MCTD extremely unlikely, a positive test at even moderately high titers of 1:160 has little or no diagnostic value .
ANA immunofluorescent staining
As our laboratory also provided information on the patterns of immunofluorescent staining, we have also been able to evaluate what further use this information might provide (previously unpublished data). Of 1369 individual patients sera tested, 445 were ANA positive in children with a known diagnosis. Of these children, 135 had a rheumatic disease (juvenile rheumatoid arthritis (JRA) (now known as JIA-the terms are used interchangeably here), SLE, MCTD, or juvenile dermatomyositis (JDM) but 310 had no convincing evidence of having a rheumatic disease.
Homogeneous, mitotic staining patterns were seen much more commonly in children with a rheumatic disease than those without (p = 0.001). Interestingly, a nucleolar pattern of staining was seen more commonly in children without a rheumatic disease (p = 0.03). This lack of an association of the nucleolar pattern in children with scleroderma specifically, and rheumatic disease in general has been c