Table 1.

Characteristics of kidney allograft recipients

VariablesACRAMRATIPa Value
Kidney allograft recipients, N262632
Urine specimens, N262632
At the time of transplant
 Age (yr), mean (SD)49 (14)47 (13)51 (15)0.50
 Women, N (%)8 (31)11 (42)13 (41)0.60
 Racial categories (black/other categories), N (%)11/15 (42/58)8/18 (31/69)9/23 (28/72)0.50
 Cause of end stage kidney disease, N (%)
  Diabetes mellitus7 (27)4 (15)6 (19)0.90
  Hypertension6 (23)7 (27)8 (24)
  GN3 (12)5 (20)6 (19)
  Others6 (23)4 (15)6 (19)
  Unknown4 (15)6 (23)6 (19)
 Donor information
  Age (yr), mean (SD)43 (21)45 (13)53 (11)0.10
  Women, N (%)15 (68)10 (45)12 (44)0.20
  Racial categories (black/other categories), N (%)4/22 (15/85)8/18 (31/69)5/27 (16/84)0.50
  Deceased donor organ, N (%)10 (38)14 (54)19 (59)0.30
 Human leukocyte antigen mismatches, mean (SD)4 (1.2)5 (1.6)4 (1.8)0.10
 Cold ischemia time (deceased donors; h), median (IQR)21 (12–29)24 (12–26)28 (18–33)0.50
 Induction therapy, N (%)
  Lymphocyte-depleting Thymoglobulin16 (62)16 (62)27b (84)0.02c
  Lymphocyte-nondepleting IL-2 receptor antibody4 (15)8 (30)5 (16)0.01d
  None6 (23)2 (8)0 (0)
After transplant and before the index allograft biopsy
 Delayed graft function, N (%)8 (31)5 (19)19 (59)0.01
 Maintenance immunosuppression, N (%)
  Tacrolimus26 (100)26 (100)32 (100)
  Mycophenolate26 (100)26 (100)32 (100)
  Corticosteroids16 (62)17 (65)7 (22)0.001
 AR, N (%)2 (8)2 (8)0 (0)
 Bacterial urinary tract infections,e N (%)9 (35)8 (31)5 (16)0.20
 BK virus nephropathy, N (%)0 (0)1 (4)0 (0)
 Cytomegalovirus disease, N (%)0 (0)0 (0)0 (0)
At the time of the index allograft biopsyf
 Time from transplantation to biopsy (mo), median (IQR)4.4 (0.6–10.5)16.2 (0.5–34.4)1.2 (0.6–2.8)0.03g
 Biopsy within 1 mo of transplantation, N (%)10 (39)9 (35)12 (38)<0.001
 Biopsy between 1 and 12 mo of transplantation, N (%)10 (39)3 (12)18 (56)
 Biopsy beyond 12 mo of transplantation, N (%)6 (23)14 (54)2 (6)
 Indication for biopsy (creatinine increase/delayed graft function), N (%)25/1 (96/4)23/3 (88/12)24/8 (75/25)0.10
 Serum creatinine (mg/dl), median (IQR)3.20 (1.90–4.33)2.62 (2.01–4.29)3.10 (2.46–5.12)0.30
 Urine protein-to-creatinine ratio, median (IQR)0.56 (0.3–2.4)1.03 (0.4–2.9)0.31 (0.2–0.9)0.10
 Serum tacrolimus trough (ng/ml), median (IQR)5.2 (4.6–8.7)6.5 (4.4–8.9)9.3 (7.8–10.4)<0.001h
 Biopsy information
  AMR (I/II/III)i1/25/0
  ACR (IA/IB/IIA/IIB/III)i5/15/4/2/0
  ATI32
  Focal necrosis/isometric vacuolization, N (%)9/20 (28/63)
  Positive staining for complement split product C4d, N (%)0 (0)26 (100)0 (0)
  Concomitant interstitial fibrosis/tubular atrophy (moderate to severe), N (%)3 (12)7 (27)1 (3)0.10
 Antibodies to one or more donor-specific human leukocyte antigens
  Data available, N (%)13 (50)22 (85)25 (78)
   MFI of the highest rank donor-specific bead<10003 (23)0 (0)17 (68)<0.001
   MFI=1000–30006 (46)2 (9)4 (16)
   MFI=3000–10,0003 (23)10 (46)3 (12)
   MFI>10,0001 (8)10 (46)1 (4)
 Urine specimens
  Collected on the day of biopsy, N (%)18 (69)18 (69)21 (66)
  Collected 1 d before/1 d after biopsy, N (%)3/5 (12/19)4/4 (15/15)2/9 (6/28)0.70
  Urine volume (ml), median (IQR)45 (28–70)43 (28–55)35 (25–45)0.10
  Urinary cell total RNA quantity (μg), median (IQR)2.1 (1.2–3.4)1.0 (0.6–2.5)1.2 (0.5–2.3)0.10
  Urinary cell total RNA purity (OD260/OD280 ratio),j median (IQR)1.97 (1.93–2.02)1.96 (1.91–1.99)1.93 (1.84–1.99)0.10
  • IQR, interquartile range; MFI, mean fluorescent intensity.

  • a P value derived by chi-squared test for categorical variables or Kruskal–Wallis test for continuous variables.

  • b Includes one patient with alemtuzumab (Campath-1H) induction.

  • c P value based on chi-squared test of independence for three rows (lymphocyte-depleting induction immunosuppression, lymphocyte-nondepleting induction, and no induction) and three columns (ACR, AMR, and ATI).

  • d P value based on chi-squared test of independence for two rows (induction immunosuppression and no induction) and three columns (ACR, AMR, and ATI).

  • e Defined as the presence of ≥105 colony forming units per milliliter of urine.

  • f Three patients (two AMR patients and one ATI patient) had BK virus replication (≥1 copy of BK virus VP1 mRNA per picogram total RNA from urinary cells) in the urine collected at the time of biopsy. None of the three patients had BK virus nephropathy (negative for SV40 staining in the biopsy tissue).

  • g P<0.05 by Dunn’s test for AMR versus ATI.

  • h P<0.05 by Dunn’s test for ACR versus ATI and AMR versus ATI.

  • i Based on the Banff 2007 update of the Banff 1997 diagnostic categories for renal allograft biopsies.

  • j Ratio of OD (absorbance of ultraviolet light) at 260 and 280 nm. Pure RNA has a ratio of approximately 2.