Dear Editor,We would like to present a case with a parainfectious dropof factor XIII (FXIII) pointing to a so far not described linkbetween coagulation and infection. A 3-year-old girl wasadmitted to our clinic due to acute joint swelling and hae-matomas during an uncomplicated infection of the upperrespiratory tract lasting since 3 weeks. The child has so farhad a normal history with respect to alimentation and de-velopment and has had the usual vaccinations. On admis-sion, the patient had haematomas at her right cheek, rightelbow andabove both heels anda mild hepatosplenomegaly.By clinical evaluation and laboratory results (Table 1), aninfection of unknown origin was suspected, presenting witha mild acute phase reaction (elevated CRP, immunoglobu-lins and fibrinogen) and signs of a mild coagulation activa-tion (indicated by slightly elevated D-dimers). A screeningshowed that the patient has already had HHV-6, HSV 1,VZV and RSV infection (IgG positive, IgM negative) andprotection from vaccination against mumps, measles andrubella. An acute infection by CMV, adenovirus, RSV, my-coplasma, cocksackie, ECHO, enterovirus, Parvo B19,EBV, Yersinia, Borrelia, Salmonella and Streptococcus pyo-genes was excluded. FXIII was very low and was the onlysignificant deviation in the coagulation system (Table 1).After a few days, the patient’s condition improved undersymptomatic therapy and could be discharged. Two weekslater, a control check-up in the outpatients’ clinic showed agood clinical recovery and normalisation of the laboratoryresults. The usual causes for FXIII deficiencies like geneticdefects[1],inhibitors, andunderlying diseases like Henoch–Schoenlein purpura, Crohn’s disease or ulcerative colitis[2-4] can be excluded by the clinical and laboratory find-ings. No interventions had taken place, which would poten-tially explain the transient deficiency. Also, it seems lessprobable that a cut coagulation activation lead to consump-tion of FXIII, as D-dimers were only slightly elevated and