Comparative evaluation of three different treponemal enzyme immunoassays for syphilis.

BACKGROUND: To reduce human errors and subjective interpretation, automation is currently a trend. However, replacing any tests with automation must first be validated. OBJECTIVE: Evaluate the EIA tests performance characteristics of three commercially available enzyme immunoassays; Enzygnost Syphilis (Dade Behring Ltd), Syphilis EIA 480 (Newmarket Laboratory Ltd) and ICE* Syphilis (Abbott Murex). MATERIAL AND METHOD: Three thousand and fifty-five serum samples were obtained from all workers who came for physical check ups before working abroad at the physical check-up unit of the out- patient department at Siriraj Hospital between February and August, 2001. Serum specimens known to be positive with VDRL and TPHA or FTA-ABS tests were included in the present study. RESULTS: Of all the samples, 2953 were from workers who came for physical check ups; 102 were selected from known specimens positive with the Venereal Disease Research Laboratory test (VDRL) and Treponema Pallidum Hemagglutination Assay (TPHA) or Fluorescent Treponemal Antibody ABSorption (FTA-ABS) test. A true positive result was determined when the sample was reactive either with two out of three enzyme immunoassays and TPHA or FTA-ABS, or both TPHA and FTA-ABS. A true negative result was determined when the aforementioned were absent. The sensitivity and specificity of Enzygnost Syphilis, Syphilis EIA 480 and ICE* Syphilis were 100% and 97.89%, 100% and 99.59%, and 99.1% and 99.76%, respectively. The results suggest that the specificity of Enzygnost Syphilis is the lowest among these three enzyme immunoassays; the price is also the cheapest. The decision to replace an existing test depends not only on the performance characteristics but also on other factors such as cost effectiveness, turnaround time, instrument maintenance, etc. The present study shows performance characteristics, whereas an economic evaluation is only briefly mentioned regarding a hospital's decision in making test selection. CONCLUSION: Among the three commercial kits, the specificity of Enzygnost Syphilis was the lowest. However, the replacement of any existing test depends greatly on the purpose of the individual laboratory whereas performance characteristics will provide us with an appropriate economic evaluation.

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 previonsly 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.

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.