Background
Methods
Selection and recruitment of participants
Recruitment source | Source description | Invitation period | Invitation type |
---|---|---|---|
Centre | Donors registered at a static donor centre | Jun 2012 – Jan 2013 | Letter |
Mobile (platelet) | Mobile session donors who had previously registered an interest in giving platelets at a static donor centre | Jan 2013 – Oct 2013 | Letter |
Mobile (10-mile) | Donors giving blood at a mobile session within 10 miles of a static donor centre | Jan 2013 – Oct 2013 | Letter or email |
Mobile (30-mile) | Donors with a correspondence address within 30 miles (but typically 20 miles) of a static donor centre | Jan 2013 – Oct 2013 | Email |
No invitation | Donors giving blood at a static donor centre who expressed an interest in joining the trial but who did not receive a previous invitation | Jun 2012 – Jun 2014 | Not applicable |
Data collection
Data analysis
Results
Participant recruitment
Participation by sources of recruitment
Invitations | Exclusions: Post-attendance and prior to consent | INTERVAL cohort and trial | ||||||
---|---|---|---|---|---|---|---|---|
Recruitment source | Invited | Attended donation | INTERVAL cohort | Randomised | Not randomised | |||
Centre | 144,852 | 71,445 | (49.3 %) | 39,500 | 31,945 | (22.1 %) | 29,549 | 2396 |
Mobile (platelet) | 21,585 | 2330 | (10.8 %) | 586 | 1744 | (8.1 %) | 1696 | 48 |
Mobile (10-mile) | 190,081 | 15,886 | (8.4 %) | 10,648 | 5238 | (2.8 %) | 5009 | 229 |
Mobile (30-mile) | 183,941 | 5524 | (3.0 %) | 3113 | 2411 | (1.3 %) | 2325 | 86 |
No invitationa | - | 10,834 | - | 3447 | 7387 | - | 6684 | 703 |
Total | 540,459 | 106,019 | 57,294 | 48,725 | 45,263 | 3462 |
Comparison of INTERVAL donors to the general donor population
Demographics | INTERVAL cohort | |||
---|---|---|---|---|
n (%) or mean (SD) | INTERVAL cohort | NHSBT general donor population | Randomised in INTERVAL trial | Not randomised |
All donors | 48,692 (100.0 %)a | 1,330,506 (100.0 %) | 45,235 (100.0 %)a | 3457 (100.0 %) |
Sex | ||||
Male | 24,212 (49.7 %) | 586,372 (44.1 %) | 22,456 (49.6 %) | 1756 (50.8 %) |
Female | 24,480 (50.3 %) | 744,134 (55.9 %) | 22,779 (50.4 %) | 1701 (49.2 %) |
Age at baseline (years) | 43.1 (14.3) | 42.3 (15.0) | 43.3 (14.2) | 39.9 (14.7) |
Age at baseline | ||||
17–24 | 6424 (13.2 %) | 234,367 (17.6 %) | 5679 (12.6 %) | 745 (21.6 %) |
25–34 | 10,236 (21.0 %) | 235,238 (17.7 %) | 9468 (20.9 %) | 768 (22.2 %) |
35–44 | 9095 (18.7 %) | 246,225 (18.5 %) | 8500 (18.8 %) | 595 (17.2 %) |
45–-54 | 11,158 (22.9 %) | 304,927 (22.9 %) | 10,456 (23.1 %) | 702 (20.3 %) |
55–-64 | 8822 (18.1 %) | 221,143 (16.6 %) | 8362 (18.5 %) | 460 (13.3 %) |
65+ | 2957 (6.1 %) | 88,606 (6.7 %) | 2770 (6.1 %) | 187 (5.4 %) |
Ethnicity | ||||
White | 44,192 (90.8 %) | 1,207,593 (90.8 %) | 41,259 (91.2 %) | 2933 (84.8 %) |
Asian | 1127 (2.3 %) | 31,829 (2.4 %) | 941 (2.1 %) | 186 (5.4 %) |
Black African | 118 (0.2 %) | 3852 (0.3 %) | 105 (0.2 %) | 13 (0.4 %) |
Black Caribbean | 307 (0.6 %) | 4971 (0.4 %) | 271 (0.6 %) | 36 (1.0 %) |
Black other | 31 (0.1 %) | 743 (0.1 %) | 29 (0.1 %) | 2 (0.1 %) |
Chinese | 164 (0.3 %) | 3831 (0.3 %) | 141 (0.3 %) | 23 (0.7 %) |
Mixed | 679 (1.4 %) | 14,838 (1.1 %) | 606 (1.3 %) | 73 (2.1 %) |
Other | 138 (0.3 %) | 3558 (0.3 %) | 122 (0.3 %) | 16 (0.5 %) |
Unknown | 1936 (4.0 %) | 59,291 (4.5 %) | 1761 (3.9 %) | 175 (5.1 %) |
Blood group | ||||
A RhD positive (A+) | 14,737 (30.3 %) | 397,277 (29.9 %) | 13,768 (30.4 %) | 969 (28.0 %) |
A RhD negative (A-) | 3744 (7.7 %) | 97,450 (7.3 %) | 3489 (7.7 %) | 255 (7.4 %) |
B RhD positive (B+) | 4244 (8.7 %) | 102,650 (7.7 %) | 3877 (8.6 %) | 367 (10.6 %) |
B RhD negative (B-) | 1070 (2.2 %) | 27,317 (2.1 %) | 993 (2.2 %) | 77 (2.2 %) |
O RhD positive (O+) | 17,642 (36.2 %) | 460,501 (34.6 %) | 16,398 (36.3 %) | 1244 (36.0 %) |
O RhD negative (O-) | 5542 (11.4 %) | 138,349 (10.4 %) | 5138 (11.4 %) | 404 (11.7 %) |
AB RhD positive (AB+) | 1293 (2.7 %) | 33,817 (2.5 %) | 1199 (2.7 %) | 94 (2.7 %) |
AB RhD negative (AB-) | 402 (0.8 %) | 9550 (0.7 %) | 368 (0.8 %) | 34 (1.0 %) |
Unknown | 18 (0.0 %) | 63,595 (4.8 %) | 5 (0.0 %) | 13 (0.4 %) |
Distance to nearest static donor centre (miles)b | ||||
0–4 | 30,405 (62.4 %) | 252,068 (18.9 %) | 27,971 (61.8 %) | 2434 (70.4 %) |
5–9 | 9801 (20.1 %) | 245,652 (18.5 %) | 9236 (20.4 %) | 565 (16.3 %) |
10–29 | 7203 (14.8 %) | 584,850 (44.0 %) | 6832 (15.1 %) | 371 (10.7 %) |
30–59 | 775 (1.6 %) | 220,388 (16.6 %) | 730 (1.6 %) | 45 (1.3 %) |
60+ | 98 (0.2 %) | 18,045 (1.4 %) | 93 (0.2 %) | 5 (0.1 %) |
Unknown | 410 (0.8 %) | 9503 (0.7 %) | 373 (0.8 %) | 37 (1.1 %) |
Donor status at baselinec | ||||
New | 1392 (2.9 %) | 288,653 (21.7 %) | 1147 (2.5 %) | 245 (7.1 %) |
Occasional | 7912 (16.2 %) | 226,507 (17.0 %) | 7053 (15.6 %) | 859 (24.8 %) |
More frequent | 39,388 (80.9 %) | 815,346 (61.3 %) | 37,035 (81.9 %) | 2353 (68.1 %) |
Donations (over last 2 years prior to baseline)d | ||||
All donations | 3.28 (2.00) | 2.24 (2.37) | 3.33 (2.00) | 2.61 (1.92) |
Whole-blood donations | 3.19 (1.81) | 2.08 (1.87) | 3.23 (1.80) | 2.55 (1.80) |
Other donations | 0.10 (1.05) | 0.16 (1.64) | 0.10 (1.07) | 0.06 (0.79) |
Deferrals (during the 2 years prior to baseline)e | ||||
Deferral for low haemoglobin | 3308 (6.8 %) | 63,071 (4.7 %) | 3094 (6.8 %) | 214 (6.2 %) |
Any other deferral | 14,628 (30.0 %) | 327,747 (24.6 %) | 13,632 (30.1 %) | 996 (28.8 %) |
Length of NHSBT donation history at baseline (years)f | 10.7 (8.4) | 8.58 (8.44) | 10.9 (8.4) | 8.47 (8.02) |
Venue type attended at baselineg | ||||
Static centre | 48,692 (100.0 %) | 99,724 (7.5 %) | 45,235 (100.0 %) | 3457 (100.0 %) |
Mobile | 0 (0.0 %) | 1,230,782 (92.5 %) | 0 (0.0 %) | 0 (0.0 %) |
Demographics | INTERVAL cohort | |||||
---|---|---|---|---|---|---|
mean or proportion (%)a | INTERVAL cohort | NHSBT general donor population | Difference (95 % CI) | Randomised | Not randomised | Difference (95 % CI) |
Sex: Male (%) | 49.7 % | 44.1 % | 5.7 % (5.2 %, 6.1 %) | 49.6 % | 50.8 % | -1.2 % (-2.9 %, 0.6 %) |
Age at baseline (years) | 43.1 | 42.3 | 0.73 (0.59, 0.87) | 43.3 | 39.9 | 3.37 (2.88, 3.86) |
Ethnicity: White (%) | 94.5 % | 95.0 % | -0.5 % (-0.7 %, -0.3 %) | 94.9 % | 89.4 % | 5.5 % (4.5 %, 6.6 %) |
Blood group: O (%)b | 47.6 % | 47.3 % | 0.4 % (-0.1 %, 0.8 %) | 47.6 % | 47.9 % | -0.2 % (-2.0 %, 1.5 %) |
Distance to nearest static donor centre (miles) | 6.29 | 18.1 | -11.8 (-12.0, -11.7) | 6.37 | 5.24 | 1.12 (0.82, 1.43) |
Number of all donationsc | 3.28 | 2.24 | 1.04 (1.02, 1.06) | 3.33 | 2.61 | 0.73 (0.66, 0.80) |
Deferral for low haemoglobin (%)c | 6.8 % | 4.7 % | 2.1 % (1.8 %, 2.3 %) | 6.8 % | 6.2 % | 0.6 % (-0.2 %, 1.5 %) |
Any other deferral (%)c | 30.0 % | 24.6 % | 5.4 % (5.0 %, 5.8 %) | 30.1 % | 28.8 % | 1.3 % (-0.2 %, 2.9 %) |
Length of NHSBT donation history at baseline (years) | 10.7 | 8.58 | 2.15 (2.07, 2.22) | 10.9 | 8.47 | 2.43 (2.14, 2.72) |
Geographical distribution of donors
Comparison of randomised versus non-randomised donors
Comparison of donors by recruitment source
Demographics | INTERVAL cohort | ||||
---|---|---|---|---|---|
n (%) or mean (SD) | Centre | Mobile (platelet) | Mobile (10-mile) | Mobile (30-mile) | No invitation |
All donors | 31,929 (100.0 %) | 1741 (100.0 %) | 5237 (100.0 %) | 2409 (100.0 %) | 7376 (100.0 %) |
Sex | |||||
Male | 15,996 (50.1 %) | 1379 (79.2 %) | 2196 (41.9 %) | 1110 (46.1 %) | 3531 (47.9 %) |
Female | 15,933 (49.9 %) | 362 (20.8 %) | 3041 (58.1 %) | 1299 (53.9 %) | 3845 (52.1 %) |
Age at baseline (years) | 43.7 (14.4) | 51.2 (13.2) | 41.9 (11.7) | 45.2 (13.6) | 38.3 (14.2) |
Age at baseline | |||||
17–24 | 3866 (12.1 %) | 82 (4.7 %) | 544 (10.4 %) | 268 (11.1 %) | 1664 (22.6 %) |
25–34 | 6688 (20.9 %) | 166 (9.5 %) | 1102 (21.0 %) | 365 (15.2 %) | 1915 (26.0 %) |
35–44 | 5849 (18.3 %) | 263 (15.1 %) | 1205 (23.0 %) | 430 (17.8 %) | 1348 (18.3 %) |
45–54 | 7233 (22.7 %) | 446 (25.6 %) | 1576 (30.1 %) | 612 (25.4 %) | 1291 (17.5 %) |
55–64 | 5938 (18.6 %) | 495 (28.4 %) | 797 (15.2 %) | 734 (30.5 %) | 858 (11.6 %) |
65+ | 2355 (7.4 %) | 289 (16.6 %) | 13 (0.2 %) | 0 (0.0 %) | 300 (4.1 %) |
Ethnicity | |||||
White | 28,924 (90.6 %) | 1644 (94.4 %) | 4774 (91.2 %) | 2227 (92.4 %) | 6623 (89.8 %) |
Asian | 790 (2.5 %) | 12 (0.7 %) | 83 (1.6 %) | 36 (1.5 %) | 206 (2.8 %) |
Black African | 78 (0.2 %) | 1 (0.1 %) | 13 (0.2 %) | 2 (0.1 %) | 24 (0.3 %) |
Black Caribbean | 201 (0.6 %) | 5 (0.3 %) | 38 (0.7 %) | 21 (0.9 %) | 42 (0.6 %) |
Black other | 24 (0.1 %) | 0 (0.0 %) | 2 (0.0 %) | 3 (0.1 %) | 2 (0.0 %) |
Chinese | 120 (0.4 %) | 1 (0.1 %) | 12 (0.2 %) | 4 (0.2 %) | 27 (0.4 %) |
Mixed | 451 (1.4 %) | 11 (0.6 %) | 67 (1.3 %) | 33 (1.4 %) | 117 (1.6 %) |
Other | 94 (0.3 %) | 2 (0.1 %) | 14 (0.3 %) | 4 (0.2 %) | 24 (0.3 %) |
Unknown | 1247 (3.9 %) | 65 (3.7 %) | 234 (4.5 %) | 79 (3.3 %) | 311 (4.2 %) |
Blood group | |||||
A RhD positive (A+) | 9414 (29.5 %) | 635 (36.5 %) | 1612 (30.8 %) | 854 (35.5 %) | 2222 (30.1 %) |
A RhD negative (A-) | 2405 (7.5 %) | 209 (12.0 %) | 371 (7.1 %) | 207 (8.6 %) | 552 (7.5 %) |
B RhD positive (B+) | 2783 (8.7 %) | 121 (7.0 %) | 436 (8.3 %) | 258 (10.7 %) | 646 (8.8 %) |
B RhD negative (B-) | 737 (2.3 %) | 45 (2.6 %) | 96 (1.8 %) | 0 (0.0 %) | 192 (2.6 %) |
O RhD positive (O+) | 11,589 (36.3 %) | 485 (27.9 %) | 1995 (38.1 %) | 1073 (44.5 %) | 2500 (33.9 %) |
O RhD negative (O-) | 3859 (12.1 %) | 199 (11.4 %) | 515 (9.8 %) | 0 (0.0 %) | 969 (13.1 %) |
AB RhD positive (AB+) | 880 (2.8 %) | 40 (2.3 %) | 164 (3.1 %) | 0 (0.0 %) | 209 (2.8 %) |
AB RhD negative (AB-) | 256 (0.8 %) | 7 (0.4 %) | 48 (0.9 %) | 17 (0.7 %) | 74 (1.0 %) |
Unknown | 6 (0.0 %) | 0 (0.0 %) | 0 (0.0 %) | 0 (0.0 %) | 12 (0.2 %) |
Distance to nearest static donor centre (miles) | |||||
0–4 | 21,298 (66.7 %) | 570 (32.7 %) | 3446 (65.8 %) | 508 (21.1 %) | 4583 (62.1 %) |
5–9 | 5778 (18.1 %) | 471 (27.1 %) | 1329 (25.4 %) | 818 (34.0 %) | 1405 (19.0 %) |
10–29 | 3946 (12.4 %) | 649 (37.3 %) | 377 (7.2 %) | 1057 (43.9 %) | 1174 (15.9 %) |
30–59 | 538 (1.7 %) | 36 (2.1 %) | 37 (0.7 %) | 13 (0.5 %) | 151 (2.0 %) |
60+ | 68 (0.2 %) | 2 (0.1 %) | 7 (0.1 %) | 7 (0.3 %) | 14 (0.2 %) |
Unknown | 301 (0.9 %) | 13 (0.7 %) | 41 (0.8 %) | 6 (0.2 %) | 49 (0.7 %) |
Donor status at baseline | |||||
New | 453 (1.4 %) | 0 (0.0 %) | 6 (0.1 %) | 8 (0.3 %) | 925 (12.5 %) |
Occasional | 4180 (13.1 %) | 35 (2.0 %) | 1039 (19.8 %) | 411 (17.1 %) | 2247 (30.5 %) |
More frequent | 27,296 (85.5 %) | 1706 (98.0 %) | 4192 (80.0 %) | 1990 (82.6 %) | 4204 (57.0 %) |
Donations (during the 2 years prior to baseline) | |||||
All donations | 3.47 (1.87) | 4.28 (1.68) | 3.06 (1.66) | 3.35 (1.75) | 2.39 (2.54) |
Whole-blood donations | 3.38 (1.73) | 4.13 (1.51) | 3.05 (1.65) | 3.33 (1.73) | 2.15 (1.92) |
Other donations | 0.08 (0.89) | 0.15 (1.08) | 0.01 (0.29) | 0.02 (0.32) | 0.23 (1.87) |
Deferrals (during the 2 years prior to baseline) | |||||
Deferral for low haemoglobin | 2597 (8.1 %) | 73 (4.2 %) | 242 (4.6 %) | 119 (4.9 %) | 277 (3.8 %) |
Any other deferral | 10,174 (31.9 %) | 461 (26.5 %) | 1238 (23.6 %) | 660 (27.4 %) | 2095 (28.4 %) |
Length of NHSBT donation history at baseline (years) | 11.2 (8.4) | 14.2 (8.4) | 10.2 (8.1) | 11.4 (9.1) | 7.78 (7.71) |