 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staining, we have also been able to evaluate what further use this information might provide (previously unpublished data).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 commented on previously [8,9].
In our lab, no combination of ANA titer, or staining pattern was specific for any particular rheumatic disease. The test combinations with the best positive predictive values for a rheumatic disease were: a) a titer ≥1:640 with mitotic positive staining or b) a titer ≥1:640 with a homogenous and mitotic staining pattern. These tests had positive predictive values of 77% and 72% respectively. Yet these results were only slightly higher than the positive predictive value of 69% obtained with a titer of ≥1:640 alone, ignoring the pattern of staining. Although the addition of patterns somewhat increases the specificity and positive predictive value of the ANA test for a rheumatic disease, it does so at the expense of both the sensitivity and negative predictive value of the test using titers alone.
The pattern of staining also does not appear to be helpful in distinguishing between rheumatic diseases. For example, although high titer homogenous, mitotic positive staining was the most common combination seen in children with SLE, it was actually found in only 27.3% of ANA positive lupus patients. This combination was also found in 12.5% of ANA positive JRA and 5.4% of ANA positive JDM patients. This lack of specificity of the ANA immunofluorescent pattern has been recognized previously, both for adults and children [8,10,11]. A study by Parker et al.  evaluated the usefulness of combining ANA titer and pattern. Although they felt that knowledge of both titer and pattern was helpful, they did not calculate specific test characteristics, and in fact no combination was restricted to any single rheumatic disease. Our assessment of these data is that the addition of information about patterns of immunofluorescence does not appear to significantly improve the utility of the ANA test.
Practical Concerns about ANA Testing
Referrals for positive ANA titers
As part of a study exploring what precipitated a referral to a pediatric rheumatologist, McGhee et al.  found that children referred, at least 