Detection of Specific Autoantibodies in Sera with Negative Antinuclear Antibody by Indirect Immunofluorescence Assay but Positive by Enzyme Immunoassay

Objective: The aim of this study was to investigate the predictive value of positive enzyme immunoassay (EIA) for detection of specific autoantibodies in sera negative for antinuclear antibody (ANA) by indirect immunofluorescence (IIF) assay, but positive for ANA by EIA. Methods: Eighty sera that tested negative for ANA by IIF, but positive for ANA by EIA were included. All sera were tested for specific autoantibodies by line immunoassay (LIA). The positive predictive value (PPV) of EIA was calculated using LIA result as a reference standard. Medical records of patients were reviewed. Clinical findings at the time of blood sampling for ANA testing and at 5 years after sampling were obtained. Results: Twenty-eight sera (35%) were found to be positive by LIA. The PPV of EIA for detection of specific autoantibodies at the manufacturer’s recommended cut-off was 35.0% (95% CI: 24.5-45.5%). The most prevalent antibodies were anti-SSA/Ro60 (64.3%, 95% CI: 46.5-82.0%), anti-Ro52 (25.0%, 95% CI: 9.0-41.0%), and anti-SSB/ La (10.7%, 95% CI: 0-22.2%). A diagnosis of systemic autoimmune rheumatic disease was established in 7 patients (25%) at the time of blood sampling, and 4 patients (14.3%) were diagnosed with non-rheumatic autoimmune disease. Conclusion: EIA testing in IIF-ANA negative sera yielded a chance to detect antinuclear antibodies. However, the poor PPV of EIA may have low benefit in real-life clinical practice. Anti-SSA/Ro60 was the most prevalent antibody detected. A high proportion of LIA-ANA positive patients were not diagnosed as autoimmune disease at the time of antibody detection

The Effect of Antinuclear Antibody Patterns on Antineutrophil Cytoplasmic Antibody Test

Antineutrophil cytoplasmic antibody (ANCA) is used to diagnose and monitor activity in the primary systemic small vessel vasculitides. Serum samples with antinuclear antibody (ANA) interfere with the reading of neutrophil indirect immunofluorescence. The question arises, will ANA pattern affect the results of ANCA test differently? To answer this question, documents were retrospectively reviewed for the criteria of ANCA test with positive ANA from January 1 to December 31, 2000. Of 137 serum specimens with ANCA and ANA tests, 58 were positive for ANA test. The result showed that the number of positive P-ANCA with homogeneous pattern of ANA (88.9%) was statistically higher than that with speckled pattern (38.78%). In conclusion, there is a different effect of various ANA patterns on ANCA results. A further prospective study is required to confirm this result

Evaluation of the Urine Dipstick Analysis for Detection of Bacteriuria

This retrospective study was performed to evaluate the urine dipstick (leukocyte esterase and nitrite test) for detection of bacteriuria and pyuria. Of the 1,000 specimens, 296 (29.6%) had positive culture results. The dipstick (either leukocyte esterase or nitrite test) test for detection of bacteriuria had a sensitivity of 85%, specificity of 51%, positive predictive value of 42% and negative predictive value of 89%, and the leukocyte esterase test for the detection of pyuria had a sensitivity of 96%, specificity of 73%, positive predictive value of 75% and negative predictive value of 95%. The sensitivity and negative predictive value of the dipstick test in the pediatric group was the lowest values when compared with the other groups. We conclude that, 1) The dipstick test may be used as a screening test for pyuria 2) This test could not be used as a screening test for urinary tract infection (UTI) 3) In contrast to sex, age affect the results of the urine dipstick test 4) This test has good result in adult particularly old age but, not in children

The Cut-off Point of Anti-dsDNA Test by EliA dsDNA

Objective: To determine the cut-off point of anti-dsDNA for screening by EliA dsDNA. Methods: Serum specimens requested for anti-dsDNA between October and December 2007 were recruited and tested by the Crithidia luciliae immunofluorescence test (CLIFT) and automated fluorescence immunoassay (EliA dsDNA). The CLIFT was considered as the gold standard method. Different levels of sensitivity and specificity were determined and the cut-off point was selected from among them. Results: Of the 133 specimens collected, 35 were positive whereas 98 were negative with the CLIFT. Of those 35 positive specimens, 2, 0, 2, 2 and 29 were, respectively, in ranges of 20 IU/ml by EliA dsDNA. Also, of the 98 negative specimens, 73, 7, 4, 4 and 10 were, respectively, in ranges of 20 IU/ml by EliA dsDNA. The sensitivity and specificity for each level were determined and the value of 11 IU/ml was selected as the cut-off point. Additionally, when clinical diagnosis was used in specimens with discrepant results, the sensitivity of EliA dsDNA was far better than the CLIFT, whereas the specificity of both methods was comparable. Conclusion: The appropriate cut-off point of EliA dsDNA for screening was 11 IU/ml. Furtermore, the diagnostic value of EliA dsDNA was better than the CLIFT when clinical diagnosis was included in the gold standard criteria

Comparison of Rheumatoid Factor Testing Methods: Nephelometric Assay Versus Latex Agglutination Assay

Rheumatoid factor (RF) is one of the criteria used for diagnosis of rheumatoid arthritis (RA). The method that has been used in our laboratory service for many years is latex agglutination assay that gives semi-quantitative results. We are going to change from this method to nephelometry that gives continuous results. The cut-off point of RF by nephelometry, comparison of these 2 methods and the 4 supplying companies were determined. Serum samples were collected from 70 patients with RA, 22 patients with various collagen diseases and 150 blood donors or normal old people. RF values by nephelometry and 4 commercial latex agglutination assays, that were latex Alexon, Shield diagnostics, Biosystem, and Behring diagnostics, were determined and compared. The results showed that the cut-off point of RF by nephelometry was 14 IU/ml and the sensitivity and the specificity was 81% and 95% respectively. The sensitivity and the specificity of latex agglutination assays by 4 companies were 76% and 94%, 68% and 97%, 62% and 98% and 64% and 98% respectively. We concluded that nephelometry gave higher sensitivity than latex agglutination assays and Latex Alexon had the highest sensitivity when comparing among the 4 companies

Reference Values of Serum Anti-streptolysin O in Adults by Nephelometry

The anti-streptolysin O (ASO) test, which depends upon age and geographic location, is used to provide evidence for antecedent streptococcal infection in patients suspected of having rheumatic fever. Reference values of ASO have not previously been determined by nephelometric assay for laboratory use at Siriraj Hospital. A total of 402 serum specimens were collected from healthy adults aged between 16 and 63 years in Siriraj Hospital. They consisted of 235 blood donors, 150 subjects who were going to study aboard and 17 dentists. ASO concentrations from 5 groups according to five age ranges were compared and it was found that two age ranges which were 25 years old and younger and 26 years and older were appropriate to determine reference values. The reference values of ASO for these two age ranges, with 90% confidence intervals, were 486 (401-673) IU/ml and 385 (362-500) IU/ml, respectively