Abnormalities of the complement system in Henoch–Schönlein purpura (HSP) have been reported, but how this abnormality in the complement system impacts on the prognosis of HSP remains unknown.

We retrospectively studied patients hospitalized for HSP in the Children’s Hospital Affiliated to Soochow University between October 2010 and May 2011. Patients with HSP and hypocomplementemia were the cases, and those without hypocomplementemia were the HSP controls. Another group of children (n = 50) with upper respiratory tract infections, but without HSP acted as negative controls.

A total number of 338 HSP patients were included in this study (n = 53 cases, n = 285 controls). In the cases, C3 and C4 levels decreased in 29 patients, C3 was low in 6, and C4 in 18. Complement levels returned to normal within 3 months in all HSP patients except one. Case group patients had higher levels of serum IgG and arthralgia, as well as positive titers of antistreptolysin-O. Rates of abdominal pain, gastrointestinal bleeding, Henoch–Schönlein purpura nephritis (HSPN), and serum IgA and IgM levels were similar in the two HSP groups.

Hypocomplementemia associated with HSP is a transient phenomenon. The incidence of significant sequelae such as HSPN between patients with and without hypocomplementemia does not differ.