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 < 5, 5 to 9.9, 10 to 14.9, 15 to 19.9 and > 20 IU/ml by EliA dsDNA. Also, of the 98 negative specimens, 73, 7, 4, 4 and 10 were, respectively, in ranges of < 5, 5 to 9.9, 10 to 14.9, 15 to 19.9 and > 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.

Prevalence of 60 kda and 52 kda Ro/SS-A autoantibodies in anti-Ro positive Thai sera in Siriraj Hospital.

BACKGROUND: Anti-Ro antibody may directly react against either Ro60 or Ro52 or both antigens. To be more applicable for routine laboratory practice, the specific antigen type for antibody detection should be identified before test application. OBJECTIVE: Investigate the prevalence of 60 kDa and 52 kDa Ro/SS-A antibodies in Thai patients' sera in Siriraj Hospital. MATERIAL AND METHOD: Specimens for anti-Ro were requested between June and December 2005. They were tested with EUROLINE test kit for prevalence determination. The principle of the test is a qualitative in-vitro-assay that contains test strips coated with parallel lines of 14 highly purified antigens. Of 84 specimens requested for anti-Ro antibody, 76 were collected and tested with the EUROLINE test kits and eight were excluded due to inadequacy. RESULTS: The prevalence of anti-Ro60 and anti-Ro52 of all sera tested for anti-Ro by EUROLINE test kit were 30% (95% CI: 20-40%) and 26% (95% CI: 16-36%), respectively; and, those in anti-Ro positive Thai sera were 82% (95% CI: 68-96%) and 71% (95% CI: 54-88%), respectively. The prevalence of anti-Ro52 alone in anti-Ro positive Thai sera and all specimens requested for anti-Ro was about 18% (95% CI: 4-32%) and 7% (95% CI: 1-13%), respectively. The agreement and Kappa value between the two methods were 0.9 and 0.77, respectively. The study suggests that the test for anti-Ro detection should provide both Ro 60 and Ro 52 antigens. CONCLUSION: The prevalence of both anti-Ro 60 and anti-Ro 52 were quite common, therefore, the test for this specific antibody should provide both antigens for antibody detection.

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.

A 20-year-old female with impending foot gangrene: How to interpret her laboratory results.

A 20-year-old female presented with multi-system involvement. At first, she had acute cholecystis and was treated by cholecystectomy. After the operation she had neurological symptoms and was diagnosed with herpes encephalitis, confirmed by CSF serology. One month later she developed left foot arterial occlusion. Autoimmune hemolytic anemia with immune thrombocytopenia (Evan’s syndrome) and myocarditis were also detected concurrently. Her primary disease was suspected to be systemic lupus erythematosus. However, her antinuclear antibody assayed by the enzyme-link immunoassay (ELISA) method was negative twice but became positive by indirect immunofluorescence method. Other positive laboratory results were lupus anticoagulant, antineutroplil cytoplasmic antibody (ANCA), and anti proteinase 3 (anti-PR3). Their relevance will be discussed in details. She was given steroids, anticoagulants and underwent a femerofemoral bypass. Her clinical status improved afterwards.

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.

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 1000 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 can 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.

Peripheral blood type 1 and type 2 T cells in Thai children with atopic diseases.

Several studies have shown that decreased IFN γ or increased IL 4 secretion by Tcells are associated with allergy and these can predict the development of atopic diseases. We compared the production of IL 4 and IFN γ in atopic Thai children with appropriate controls. Twenty five atopic patients and twenty four non-atopic subjects were enrolled. Production of IFN γ and IL 4 by peripheral blood mononuclear leukocytes was measured under stimulating conditions (phorbol myristate acetate). The atopic group comprised 6 atopic asthmatics and 19 allergic rhinitis patients. The results showed no significant difference in the IFN γ/ IL 4 ratio between atopic asthmatics, and allergic rhinitis patients and controls. However, the difference between asthmatics and controls was larger than between the other groups. In this study, a nonsignificant trend of overproduction of IL 4 compared with IFN γ is shown only in asthmatic children as compared to those with rhinitis and controls.

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, Biosyste, and Behring diagnostics, were determned 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 specificty 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 asssay and Latex Alexon had the highest sensitivity when comparing among the 4 companies.