title: Clinical validation of immunoglobulin A nephropathy diagnosis in Swedish biopsy registers.
abstract: OBJECTIVE
  The aims of this study were to validate the diagnosis of IgA nephropathy (IgAN) in Swedish biopsy registers against patient charts and to describe the clinical characteristics of patients with a biopsy indicating IgAN.
  
  
  METHODS
  This is a population-based cohort study. Out of 4,069 individuals with a renal biopsy consistent with IgAN (biopsies performed in 1974-2011), this study reviewed patient charts of a random subset of 127 individuals. Clinical and biopsy characteristics at the time of biopsy were evaluated, and positive predictive values (PPV) were calculated with 95% confidence intervals (CI).
  
  
  RESULTS
  Out of 127 individuals with a renal biopsy consistent with IgAN, 121 had a likely or confirmed clinical diagnosis of IgAN, primary or secondary to Henoch-Schönlein purpura, yielding a PPV of 95% (95% CI =92%-99%). The median age at biopsy was 39 years (range: 4-79 years); seven patients (6%) were <16 years. The male to female ratio was 2.8:1. The most common causes for consultation were macroscopic hematuria (n=37; 29%), screening (n=33; 26%), and purpura (n=14, 11%). In patients with available data, the median creatinine level was 104 μmol/L (range 26-986 μmol/L, n=110) and glomerular filtration rate 75 mL/min/1.73m2(range 5-173 mL/min/1.73m2, n=114). Hypertension was noted in 59 (46%) individuals. IgA deposits were reported in 97% of the biopsy records (n=123), mesangial hypercellularity in 76% (n=96), C3 deposits in 89% (n=113), and C1q deposits in 12% (n=15).
  
  
  CONCLUSIONS
  A histologic diagnosis of IgAN has a high PPV for a diagnosis of IgAN confirmed by review of patient charts.
authors.affiliation: Department of Pediatrics, Faculty of Health and Medicine, Örebro University; Department of Pediatrics, Örebro University Hospital, Örebro.
authors.forename: Simon
authors.initials: S
authors.lastname: Jarrick
authors.affiliation: Department of Nephrology, Karolinska University Hospital; Department of Clinical Science, Intervention and Technology, Karolinska Institutet.
authors.forename: Sigrid
authors.initials: S
authors.lastname: Lundberg
authors.affiliation: Boston Consulting Group; Clinical Epidemiology Unit, Department of Medicine.
authors.forename: Adina
authors.initials: A
authors.lastname: Welander
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine.
authors.forename: C Michael
authors.initials: CM
authors.lastname: Fored
authors.affiliation: Department of Pediatrics, Örebro University Hospital, Örebro; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Division of Epidemiology and Public Health, School of Medicine, University of Nottingham, Nottingham, UK.
authors.forename: Jonas F
authors.initials: JF
authors.lastname: Ludvigsson
keywords: IgA nephropathy; general population-based; histopathology; kidney; renal disease; validation studies