Table 3. Outcomes for the Study of Small-Volume vs Standard-Volume Tubes for Blood Collection.
| Primary population (n = 21 201)a | ||||
|---|---|---|---|---|
| Small-volume tubes (n = 10 261) | Standard-volume tubes (n = 10 940) | Relative risk (95% CI)b | Mean difference (95% CI)b | |
| Primary outcome | ||||
| RBC units transfused in ICU per patient per median ICU stay | ||||
| Least-squares mean (95% CI) | 0.72 (0.52 to 0.98) | 0.79 (0.58 to 1.07) | 0.91 (0.79 to 1.05)c | −0.07 (−0.19 to 0.03) |
| Crude mean (SD) | 0.78 (2.23) | 0.88 (2.79) | ||
| Secondary outcomes | ||||
| Specimens with insufficient quantity for analysis, No. (%)d | 42 (0.022)e | 60 (0.031)e | −0.009 (−0.02 to 0.001)f | |
| Patients received ≥1 units RBC transfusion in ICU, No. (%) | 2975 (29.0) | 3387 (31.0) | 1.01 (0.93 to 1.09) | 0.16 (−2.19 to 2.34)f |
| Change in hemoglobin from ICU admission to ICU discharge adjusted for RBC transfusions, median (IQR), g/dLg,h,i | −1.40 (−3.00 to −0.20) | −1.50 (−3.20 to −0.40) | 0.10 (−0.04 to 0.23) | |
| Duration of ICU admission, median (IQR), d | 4.0 (3.0 to 8.0) | 4.0 (3.0 to 7.0) | 0.97 (0.93 to 1.02) | −0.18 (−0.47 to 0.10) |
| Duration of hospital admission, median (IQR), d | 11.0 (7.0 to 20.0) | 11.0 (7.0 to 18.0) | 1.03 (1.00 to 1.06) | 0.35 (−0.05 to 0.74) |
| Mortality in ICU, No. (%) | 1492 (14.5) | 1294 (11.8) | 0.97 (0.86 to 1.10)j | −0.37 (−2.13 to 1.20)f |
| Mortality in hospital, No. (%) | 1812 (17.7) | 1631 (14.9) | 0.98 (0.88 to 1.09)j | −0.34 (−2.22 to 1.35)f |
| Post hoc exploratory outcomes | ||||
| Hemoglobin within 48 h of ICU discharge, median (IQR), g/dLg,i | 9.50 (8.30 to 11.20) | 9.50 (8.30 to 11.10) | 1.01 (1.00 to 1.02) | 0.09 (0.002 to 0.18) |
| Change in hemoglobin from ICU admission to ICU discharge, median (IQR), g/dLg,i | −0.80 (−1.90 to 0.20) | −0.90 (−2.10 to 0.10) | 0.10 (0.02 to 0.18) | |
| Change in hemoglobin from ICU admission to ICU discharge in patients without RBC transfusions, median (IQR), g/dLg,k | −0.80 (−1.90 to 0.10) | −1.00 (−2.10 to 0.00) | 0.10 (0.01 to 0.19) | |
Abbreviations: ICU, intensive care unit; RBC, red blood cell.
Patients admitted during the COVID-19 pandemic-related delay in transitions to small-volume tubes (March 2, 2020, -August 17, 2020) were excluded.
Values were adjusted for age and sex and accounted for the stepped-wedge design with periods modeled as fixed effects, ICU units as a random effect, and for the primary outcome, length of ICU stay as an offset.
P = .19 for this relative risk, which represents the result of the hypothesis test for the significance of the intervention (transition to small-volume tubes) effect and was calculated by generalized linear mixed model, adjusted for age and sex, and accounted for the stepped-wedge design.
Number of tubes with insufficient quantity for analysis per total number of specimens sent for hemoglobin (ethylenediaminetetraacetic acid tubes) and creatinine (lithium or sodium heparin tubes) tests during ICU admission; analyzed using χ2 test of equality of 2 proportions.
Denominators were 193 695 for the small-volume tube group vs 195 383 for the standard-volume tube group.
Difference in % was presented for binary outcomes and was adjusted for age and sex and accounted for the stepped-wedge design. Absolute difference in % without any adjustment was presented for specimens with insufficient quantity outcome.
Analyses were adjusted for baseline admission hemoglobin in addition to adjusting for age and sex.
Hemoglobin was adjusted for RBC transfusion (1 transfusion = Hb – 1 g/dL). Values less than 0 were substituted with 0 (3.9% of values).
Denominators were 9260 for the small-volume tube group vs 9820 for the standard-volume tube group.
Unadjusted relative risk for mortality in ICU was 1.23 (95% CI, 1.15 to 1.32), and for mortality in hospital it was 1.18 (95% CI, 1.11 to 1.26).
Denominators were 6377 for the small-volume tube group vs 6645 for the standard-volume tube group.