Introduction Mannose binding lectin (MBL) plays a crucial part in innate immunity by activating the complement pathway. MBL deficiency is common, it has been associated with pulmonary disease, but low levels may also be found in otherwise normal individuals. Little is known about the importance of MBL deficiency as a risk factor for recurrent upper and lower respiratory tract infections.1 2 We describe our experience of measuring MBL levels in children with recurrent upper and lower respiratory tract infections.

Methods MBL levels and clinical data were extracted from immunology laboratory records, of children being investigated for acute or chronic recurrent respiratory tract infections between November 2008 and February 2010. MBL deficiency was defined as a level <75 ng/ml.

Results 489 children had serum MBL measured during this time period. 199 had recurrent respiratory infections and of those 36 were positive for MBL deficiency (Abstract S29 Figure 1). Deficiency was found in 29% of positive boys and 14% of positive girls. 20% of positive patients were <2 years, 16% 2–5 years and 28% >5 years at the time of investigation.

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Abstract S29 Figure 1

The distribution of clinical problems of MBL deficient children.

Conclusions MBL deficiency is common in our population. The true significance of this abnormality as a risk factor for respiratory infection in children remains to be determined. Case–control studies will be required to evaluate the relative importance of this abnormality in different subgroups of patients.