Table 2

Descriptive statistics (median, lower and upper quartile) at baseline by dichotomised entry diagnosis microscopic polyangiitis (MPA) and Wegener's granulomatosis (WG)

N (n)MPA (N=254)WG (N=281)Combined (N=535)Test statistic p value
Sex535
 Male52% (133)55% (155)54% (288)0.521
 Female48% (121)45% (126)46% (247)
Age years53554 64 7043 58 6649 61 69<0.0012
Entry age quartile<0.0011
 <50 years19% (48)33% (93)26% (141)
 50–60 years18% (46)24% (67)21% (113)
 60–70 years37% (94)27% (76)32% (170)
 >70 years26% (66)16% (45)21% (111)
Serum creatinine µmol/l535 (523)174 335 65482 107 29297 203 498<0.0012
GFR ml/min5357.2 14.7 31.818.8 59.2 79.69.6 27.9 64.7<0.0012
GFR categorised as CKD stage535<0.0011
12% (4)15% (41)8% (45)
25% (13)34% (95)20% (108)
320% (51)17% (49)19% (100)
423% (58)14% (38)18% (96)
550% (128)21% (58)35% (186)
CKD stage trichotomised535<0.0011
A7% (17)48% (136)29% (153)
B43% (109)31% (87)37% (196)
C50% (128)21% (58)35% (186)
Haemoglobin g/dl535 (502)8.6 9.4 10.78.7 10.2 11.98.6 9.8 11.5<0.0012
WBC 109/l535 (502)8.1 10.4 13.18.8 11.1 14.38.4 10.8 13.7<0.0212
Platelets 109/l535 (501)254 330 436301 400 534276 364 482<0.0012
CRP mg/l535 (485)13 41 9821 65 14218 54 118<0.0012
ANCA ELISA only535<0.0011
MPO58% (148)9% (26)33% (174)
PR325% (64)79% (222)53% (286)
Double positive; MPO and PR32% (4)4% (12)3% (16)
Negative13% (32)7% (19)10% (51)
Missing2% (6)1% (2)1% (8)
ANCA ELISA or IIF535<0.0011
MPO67% (169)13% (36)38% (205)
PR326% (65)79% (223)54% (288)
Double positive; MPO and PR32% (4)4% (12)3% (16)
Negative4% (10)3% (8)3% (18)
Missing2% (6)1% (2)1% (8)
BVAS535 (504)13 15 2112 20 2612 17 23<0.0012
BVAS quartiles<0.0011
<1011% (28)15% (42)13% (70)
10–1853% (134)23% (64)37% (198)
18–2318% (46)24% (67)21% (113)
>2318% (46)38% (108)29% (154)
  • N observations after single imputation (n) observations before single imputation test statistic used1Pearson test,2Wilcoxon test.

  • ANCA, antineutrophil cytoplasmic antibodies; BVAS, Birmingham Vasculitis Activity Score; CKD, chronic kidney disease; CRP, C-reactive protein; GFR, glomerular filtration rate; IIF, immunofluorescence microscopy; MPA, microscopic polyangiitis; MPO, myeloperoxidase; PR3, proteinase 3; WBC, white blood cell count; WG, Wegener's disease.