Chlamydia pneumoniae IgG seropositivity in deep-vein thrombosis

Abstract

Boulos Maraha and colleagues' data showed an overall 75% agreement when the MIF test (cut off >16) and ELISA assay (>1·1) were compared in several groups. This proportion is similar to between-laboratory variation in MIF assay results (80% agreement), which reflects the lack of standardisation for performance of the MIF test.1Peeling RW Wang SP Grayston JT et al.Chlamydia pneumoniae serology: interlaboratory variation in microimmunofluorescence assay results.J Infect Dis. 2000; 181: 426-429Crossref Scopus (122) Google Scholar We saw a good correlation between three ELISA methods, with different C pneumoniae-specific antigens, for test outcome (positive/negative) and strength of ELISA reactivity in more than 200 patients (r>0·85, p<0·001). We did not compare ELISA with MIF assays for IgG reactivity. However, several reports have shown that the ELISA is in good qualitative agreement with the MIF assay and that a widely accepted gold standard for C pneumoniae infection is still lacking.2Persson K Haidl S Evaluation of a commercial test for antibodies to the chlamydial lipopolysaccharide (Medac) for serodiagnosis of acute infections by Chlamydia pneumonia (TWAR) and Chlamydia psittaci.APMIS. 2000; 108: 131-138Crossref PubMed Scopus (21) Google Scholar, 3Verkooyen RP van Lent NA Mousavi Joulandan SA et al.Diagnosis of Chlamydia pneumonia infection in patients with chronic obstructive pulmonary disease by micro-immunofluorescence and ELISA.J Med Microbiol. 1997; 46: 959-964Crossref PubMed Scopus (33) Google Scholar, 4Verkooyen RP Willemse D Hiep-van Casteren SC et al.Evaluation of PCR, culture, and serology for diagnosis of Chlamydia pneumoniae respiratory infections.J Clin Microbiol. 1998; ß36: 2301-2307Google Scholar In the meantime, the abstract data of O Lozinguez and colleagues appeared in a full article.5Lozinguez O Arnaud E Belec L et al.Demonstration of an association between Chlamydia pneumoniae infection and venous thromboembolic disease.Thromb Haemost. 2000; 83: 887-891PubMed Google Scholar We conclude that their and our findings are similar; we saw 78-80% IgG seropositivity to C pneumoniae among thrombosis patients and healthy controls (odds ratio 1·1). In addition thrombosis risk at higher ELISA reactivity did not increase. The IgG seropositivity (defined by the manufacturer as an MIF titre ≥128) was strikingly similar in cases (75%) and controls (81%) and there was no increase in thrombosis risk for participants with positive IgG serology for C pneumoniae. Only in a subanalysis did Lozinguez show that participants with an IgG titre of 256 or more had a seven-fold increase in thrombosis risk compared with those who had lower titres. However, participants with IgG titres between 128 and 256 had a significant 80% reduction in thrombosis risk compared with the reference category (IgG titre <128). From a biological point of view these findings are difficult to interpret. We do not take positive C pneumoniae serology to be a proven risk factor for venous thrombosis. We would stress the need for standardisation of the MIF test and further comparisons of the MIF test and ELISA assay for C pneumoniae serostatus.