DETECTION OF ANTINEUTROPHIL CYTOPLASMIC ANTIBODIES IN PRIMARY SCLEROSING CHOLANGITIS - A COMPARISON OF THE ALKALINE-PHOSPHATASE AND IMMUNOFLUORESCENT TECHNIQUES

Background: The reported prevalence of antineutrophil cytoplasmic anti bodies (ANCA) in primary sclerosing cholangitis (PSC) varies considera bly (26-85%). Part of this may reflect methodological differences but part may reflect the differences in the patient groups analysed. To re solve this issue we compared the sensitivity and specificity of the im munoalkaline phosphatase (IALP) and immunofluorescence (IF) techniques in four different populations. Method: Sera from four centres were te sted blind on alcohol-fixed neutrophils using both techniques. Patient s: USA: 14 PSC, 14 primary biliary cirrhosis (PBC); Sweden: 32 PSC, 3 autoimmune hepatitis (AIH), 14 PBC, 11 chronic liver disease; Norway: 32 PSC, 14 AIH, 13 PBC, 1 hepatitis C. Italy: 8 PSC, 14 PBC, 8 viral h epatitis. Thirty-six normal healthy volunteers from Oxford, together w ith positive and negative controls, were also tested. Results: The hea lthy controls were all ANCA negative. The diagnostic sensitivity and s pecificity, respectively, of ANCA for PSC using the IALP technique for the different test sera were: USA 71% and 93%, Sweden 66% and 96%, No rway 69% and 46%, Italy 50% and 95%. The diagnostic sensitivity and sp ecificity, respectively, of the IF technique on the same sera were: US A 50% and 86%, Sweden 56% and 86%, Norway 47% and 61%, Italy 50% and 9 1%. Overall, combining all four groups, detection of ANCA using the IA LP technique gave a diagnostic sensitivity of 66% with a specificity o f 74% for PSC. In contrast, the IF technique gave an overall diagnosti c sensitivity of only 51% (P=0.044, compared with IALP) with a specifi city of 73%. Although overall the IALP technique was more sensitive th an IF, the differences in sensitivity and specificity between the two techniques did not reach statistical significance for any individual g roup. Furthermore, the small differences in sensitivity between the fo ur groups using either technique were not significant. However, the IA LP technique had greater specificity in the US, Swedish and Italian gr oups compared with the Norwegian group (P<0.05) whereas no statistical ly significant differences in specificity were noted between the group s using the IF technique. Conclusion: This study shows that the IALP m ethod of ANCA detection is at least as sensitive as IF for the serolog ical diagnosis of PSC. Indeed, combining data from all four centres, t he IALP technique was significantly more sensitive than IF. We therefo re recommend the use of the IALP technique, which is also easier to in terpret and does not require the use of a specialist fluorescent micro scope. The lack of a wide variation in sensitivity between IALP and IF for any individual patient group reported in this study suggests that the previously reported regional differences in ANCA prevalence in PS C of between 26% and 85% may be patient related, rather than due to et hnic or methodological differences in ANCA detection, perhaps reflecti ng possible disease heterogeneity within PSC, or case selection bias. Further studies are needed to investigate this intriguing possibility. Such differences, if confirmed, will need to be taken into account wh en assessing the use of ANCA as a serological marker of PSC.