[Accuracy and diagnostic utility of IgM in Bartonella henselae infections].

INTRODUCTION: Laboratory diagnosis of cat scratch disease (CSD) is based on the determination of specific antibodies anti-Bartonella henselae by different techniques. The CDC recommends IgG by immunofluorescent assay (IFA) as the gold standard.

OBJECTIVE: To determine the accuracy and diagnostic utility of anti-B.henselae IgM by IFA for CSD.

MATERIAL AND METHODS: Anti-B. henselae IgG was determined in serum of 108 patients with CSD suspicion; in addition, specific IgM was determined separately and blindly by two thoroughly trained laboratory professionals. We calculated sensitivity (S), specificity (Sp), predictive values both positive (PPV) and negative (NPV), and likelihood ratio (LR) for IgM positive (LR +) and negative (LR-).

RESULTS: In 37 patients with positive anti-B.henselae IgG, IgM was positive in 16 and negative in 21; in 71 patients with negative IgG, IgM was negative in 69 and positive in 2. Therefore, IgM showed S 43%, E 97%, PPV 88%, NPV 77%, LR (+) 15 and LR (-) 0.58.

CONCLUSIONS: The results show that a positive IgM supports, but a negative one does not rule out a B. henselae infection. Therefore, IgG should be still considered as the gold standard for the diagnosis of CSD.