ABSTRACT
Objective To compare and evaluate the usefulness of diagnostic tests of IFA with HEp-2 cell substrate and ELISA coated with purified nuclear antigens for ANA in SLE.Methods Sera derived from 226 SLE cases and 183 healthy controls were tested for ANA and all parameters were compared such as sensi- tivity,specificity,accuracy,positive predictive value,negative predictive value,positive likelihood ratio,nega- tive likelihood ratio,result consistency,rank correlation coefficient and kappa of ANA detected by IFA and ELISA.Accuracy was evaluated by ROC for two methods.All 36 samples with different results from two meth- ods were detected for ENA.The correlation of titer to A ratio of different patterns as studied.Results The sensitivity of IFA and ELISA was 91.15% and 92.04% respectively for SLE patients,specificity was 96.17% and 92.90%,accuracy was 93.40% and 92.42%,positive predictive value was 96.71% and 94.12%,negative predictive value was 89.80% and 90.43%,no significant difference was found between the two methods (P＞0.05).No significant difference was found in accuracy of both methods by ROC (P=0.409).Good agreement was found between two methods with rank correlation coefficient (R=0.823) and kappa (k=0.825).All of 36 samples with different ANA results from two methods were detected for ENA.In 14 cases with IFA positive and ELISA negative,the titer of one case was up to 1:1000 and the pattern was Golgi by IFA,the titers of the rest were about cutoff level and the pattern were granular and nucleolus mostly.In 22 cases with IFA nega- tive and ELISA positive,11 cases of them had the A ratio ranged from 2.67～30.5.Positive rate of ENA was 14.29% in 14 cases with IFA positive and ELISA negative,68.18% in 22 eases with IFA negative and ELISA positive and the difference was significant (P＜0.01).Poor correlation of titer to A ratio for granular pattern samples (R=0.083),but good correlation for homogeneous pattern was found (R=0.595).Conclusion IFA as the recommended detecting method for ANA is intuitive and can provide more information by different pattem than ELISA but it needs fluorescence microscope and experienced technician.While ELISA is very simple and the concentration of ANA can be evaluated by A ratio value.ELISA can be a substitute method for ANA be- cause both IFA and ELISA have high sensitivity,specificity,accuracy,agreement rate,kappa and rank correla- tion coefficient.In addition,ELISA is more accessable for screen test because of low rate of false negative re- sult.Result of ELISA is more accurate if new and uncommon antigens are coated such as Golgi and nucleolus. The new work flow in which ELISA is used to screen out the positive ANA samples and IFA is used then to detect the nuclear pattern of ANA can save time,cost,and in turn improve work efficiency.