The TESTING (Therapeutic Evaluation of STeroids in IgA Nephropathy Global) study is a multicenter, double-blinded, randomised, placebo-controlled trial designed to evaluate the long-term efficacy and safety of oral methylprednisolone, on a background of routine renin angiotensin system (RAS) inhibitor therapy, in preventing kidney events in patients with IgA nephropathy with features suggestive of a high risk of disease progression. This statistical analysis plan (SAP) provides the details of all pre-specified analyses to be conducted at the end of the trial. The SAP was written by the trial statistician, chief investigator, study director and project manager and approved by the management committee.