Impact of systematic variations in hematocrit and platelet count on thrombelastometry tissue factor activated assay parameters.

BACKGROUND: Thromboelastogram testing is increasingly being used to manage patients with massive bleeding. An earlier study found that the test results were influenced by the hematocrit (Hct) and platelet (PLT) concentrations. This study sought to determine if these factors confounded the results of a different manufacturer's thromboelastography testing. METHODS: Using freshly collected whole blood from volunteers and stored red blood cells (RBC) and plasma, the whole blood was manipulated to achieve different Hct values and PLT concentrations. Each reconstituted whole blood sample was tested in triplicate on the ROTEM Delta device and the ExTEM results were recorded. RESULTS: Many of the ExTEM results varied according to the Hct and PLT concentration. In particular, the ExTEM clot formation time (CFT) was abnormally long when the Hct was 45% and the PLT concentration was ≤75 × 109/L, normalizing only when the PLT count was ≥100 × 109/L. CFT samples with Hct 25% and 35% were also abnormal with low PLT concentrations but normalized at lower PLT concentrations compared to the Hct 45% samples. The ExTEM angle also demonstrated abnormal results when the Hct was 45% and the PLT concentration was ≤50 × 109/L. The ExTEM A10 and maximum clot firmness (MCF) tests tended to also be abnormal when the Hct was between 25% and 45% and the platelet concentrations were below 75 × 109/L. CONCLUSION: While thromboelastogram testing is gaining popularity for managing bleeding patients, clinicians should be aware of these confounding factors when making transfusion decisions based on their results.

SARS-CoV-2 antibody kinetics in blood donors with a previously positive SARS-CoV-2 antibody test within a seroprevalence survey.

The persistence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies is a matter of importance regarding the coronavirus disease 19 (COVID-19) pandemic. To observe antibody dynamics, 105 blood donors, positive for SARS-CoV-2 antibodies by a lateral flow test within a seroprevalence study, were included in this study. Thirty-nine (37%) of 105 the donors were confirmed positive by a total Ig Wantai enzyme-linked immunosorbent assay (ELISA). Three (8%) in this group of 39 reported severe and 26/39 (67%) mild to moderate COVID-19 symptoms. By further ELISA-testing, 33/39 (85%) donors were initially positive for IgG antibodies, 31/39 (79%) for IgA, and 32/39 (82%) for IgM, while 27/39 (69%) were positive for all three isotypes. Persistence of IgG, IgA, and IgM was observed in 73%, 79%, and 32% of donors, respectively, after 6-9 months of observation. For IgM antibodies, the decline in the proportion of positive donors was statistically significant (p = 0.002) during 12 months observation, for IgG only the decline at 3 months was statistically significant (p = 0.042). Four donors exhibited notable increases in antibody levels. In conclusion, persistent SARS-CoV-2 IgA antibodies and IgG antibodies at 6-9 months are present in approximately three of four individuals with previous mild to moderate COVID-19.

Quantification of anti-A of IgM or IgG isotype using three different methodologies.

BACKGROUND: Reliability of ABO-antibody measurement is important in the context of supplying low-titer ABO incompatible plasma-containing blood products. This study investigated the correlation of anti-A measurements between three different titer methodologies. METHODS: Thirty-four blood group O individuals were included. IgM and IgG anti-A was measured by three different methods: (1) manual method (Bio-Rad ID-gel card), (2) automated method (Immucor NEO), (3) flow cytometry (FC) with calibration in molecules of equivalent fluorochrome (MEF). Data were log2 transformed to titer steps (TS) and log2 MEF, respectively. All three methods were benchmarked against the 14/300 WHO anti-A/anti-B standard reagent. RESULTS: The correlation between the manual and automated methods was statistically significant for both IgM (Spearman's rs  = 0.89, p < .0001) and IgG (rs  = 0.95, p < .0001). The mean TS difference between the manual and automated methods was 0.61 for IgM (p = .0033) and 2.1 for IgG (p < .0001). The manual method yielded IgM titer results that were generally 1 titer step higher than the automated method, whereas for the IgG titrations the difference was generally a median of 2 TS higher. The FC median log2 MEF level was significantly correlated with TS of IgG and IgM for both manual and automated agglutination-based titer methods (0.69 ≤ r2  ≤ 0.91). With the WHO standard reagent, the manual method produced the expected results while the automated method's results were 1 TS lower for both IgM and IgG at all dilutions tested. CONCLUSION: These results indicate that all three methods are suitable for measuring anti-A in group O whole blood.

Time-related variation in IgG subclass concentrations in a group of healthy Danish adults.

INTRODUCTION: Immunoglobulin G subclass measurements are important for the diagnostic work-up of immunodeficiencies and immunoglobulin G4 (IgG4) related diseases. It is currently unknown whether a single sampling is truly representative for an individual's IgG subclass concentrations. This study aimed to investigate whether IgG and IgG subclass concentrations in healthy individuals are stable over time. METHOD: With a span of median 42 weeks, four samples from each of 54 (34M, 20F) healthy adult volunteers (24-66 years) were analyzed for IgG and IgG1-4 using turbidimetry. Concentrations were compared within and between individuals. RESULTS: IgG and IgG subclass concentrations followed either a normal (IgG, IgG1, and IgG3) or log normal (IgG2 and IgG4) distribution. Immunoglobulin 4 demonstrated by far the widest range of concentrations between individuals (670-fold: 0.004-2.68 g/L). Immunoglobulin G subclass variations within individuals were expressed as pooled standard deviations (PSD). These ranged from 0.056 (IgG4) to 0.955 g/L (IgG) and correlated with mean concentration of IgG or the particular IgG subclass. As a consequence, the relative PSDs (i.e., PSD divided by mean IgG or IgG subclass concentration) fell within a narrow range: 5.82%-10.1%. Based on these numbers, the 95%-upper one-sided confidence limits for intraindividual IgG and IgG subclass variation was calculated to range from 9.82% (IgG2) to 16.9% (IgG4). CONCLUSION: The study documents that IgG or IgG subclass concentrations within healthy individuals are very stable over at least 42 weeks. The expected variation for IgG4 concentrations at a 95% confidence level does not exceed ±16.9%.

Impact of RHD genotyping on transfusion practice in Denmark and the United States and identification of novel RHD alleles.

BACKGROUND: Reduced D antigen on red blood cells (RBCs) may be due to "partial" D phenotypes associated with loss of epitope(s) and risk for alloimmunization or "weak" D phenotypes that do not lack major epitopes with absence of clinical complications. Genotyping of samples with weak and discrepant D typing is recommended to guide transfusion and RhIG prophylaxis. The goal was to compare the impact of RHD genotyping on transfusion practice in two centers serving different populations. STUDY DESIGN AND METHODS: Fifty-seven samples from Denmark and 353 from the United States with weak or discrepant D typing were genotyped. RBC typing was by multiple methods and reagents. DNA isolated from white blood cells was tested with RBC-Ready Gene D weak or CDE in Denmark or RHD BeadChip in the United States. RHD was sequenced for those unresolved. RESULTS: Of Caucasian samples from Denmark, 90% (n = 51) had weak D types 1, 2, or 3; two had other weak D, two partial D, and two new alleles. In diverse ethnic U.S. samples, 44% (n = 155) had weak D types 1, 2, or 3 and 56% (n = 198) had other alleles: uncommon weak D (n = 13), weak 4.0 (n = 62), partial D (n = 107), no RHD (n = 9), and new alleles (n = 7). CONCLUSION: Most samples with weak or variable D typing from Denmark had alleles without risk for anti-D. In U.S. samples, 48% could safely be treated as D+, 18% may require consideration if pregnancy possible, and 34% could potentially benefit from being treated as D-. Black and multiracial ethnicities were overrepresented relative to population.

ABO blood group is related to bleeding in cardiac surgery.

BACKGROUND: Increased bleeding and blood product transfusions during cardiac surgery are associated with poor outcomes. The patient's ABO blood group is related to hemostatic balance, although it is unclear whether this influences bleeding during cardiac surgery. This study aimed to evaluate whether ABO blood group is related to bleeding during cardiac surgery. METHODS: This retrospective study evaluated data from 17,058 cardiac surgical procedures that were performed in four Danish cardiosurgical centers. Data regarding chest tube drainage and transfusion volumes were retrieved from a clinical database and combined with information regarding ABO group. The primary outcome was chest tube drainage volume and the secondary outcomes were transfused volumes of various blood products. RESULTS: Blood group O had the largest chest tube drainage volume (mean: 745 mL, 95% CI: 720-771 mL) and blood group AB had the smallest volume (mean: 664 mL, 95% CI: 598-731 mL). The inter-group difference in the mean drainage volume was 81 mL (95% CI: 8-154 mL, P < .05). Patients with blood group A or blood group B had mean drainage volumes that were between the volumes for groups AB and O. Relative to group O, group AB received smaller mean volumes of all blood products. The most pronounced difference was in platelet concentrates, with mean values of 170 mL for group O (95% CI: 157-184 mL) and 63 mL for group AB (95% CI: 34-92 mL). CONCLUSION: The patient's ABO group appears to be related to volumes of chest tube drainage and transfused blood products during cardiac surgery.

Comparison of six commercially available SARS-CoV-2 antibody assays-Choice of assay depends on intended use.

OBJECTIVES: Evaluate six commercial serological assays for detection of IgA, IgM or IgG SARS-CoV-2 antibodies in different disease severities. METHODS: Three lateral flow tests (LFTs) (Acro IgM/IgG, CTK IgM/IgG, Livzon IgM/IgG) and three ELISA assays (Euroimmun IgA and IgG, Wantai IgM) were included. Application was evaluated using samples from 57 patients with a positive SARS-CoV-2 reverse transcription polymerase chain reaction, stratified according to disease severity. Specificity was assessed using historical samples from 200 blood donors. RESULTS: While IgM LFTs failed to detect SARS-CoV-2 antibodies in 37-84% of non-hospitalised patients, the Wantai IgM ELISA detected antibodies in 79%. The Euroimmun IgG ELISA detected antibodies in 95% of non-hospitalised patients. IgA, IgM and IgG ELISA levels were initially low, increased over time, and correlated with disease severity. LFT sensitivity declined in samples taken >28 days after symptom onset/resolution. The Livzon IgG LFT had the highest specificity (98.5%), followed by the Euroimmun IgG ELISA (96.2%). The specificity for Euroimmun IgA ELISA improved (≥97.5%) using a custom cut-off value (4.0). CONCLUSIONS: The sensitive and semi-quantitative ELISA assays are most appropriate for serologic detection of SARS-CoV-2 infection in mild cases. Livzon LFT and Euroimmun ELISA had the highest specificity among the IgG assays, making them most suitable for seroprevalence studies.

A novel ABO allele with a 21-bp duplication identified in two unrelated European individuals with weak A expression.

OBJECTIVES: To carry out genetic and serological analyses of a Swiss blood donor and a Danish patient carrying an aberrant ABO phenotype with weak A expression. BACKGROUND: ABO is the most clinically important blood group system but also one of the most complex. The system antigens are determined by carbohydrate structures generated by A and B glycosyltransferases encoded by the ABO gene. Genetic variants of ABO may encode a glycosyltransferase with reduced activity, leading to weak expression of A antigen. METHODS: Samples from two individuals were examined using genetic testing and extended immunohaematological evaluation, including standard serological methods, flow cytometry and analysis of plasma glycosyltransferase activity. RESULTS: Both individuals were serologically determined to be Aweak B. Genetic testing revealed that both were heterozygous for a novel ABO*A1.01-like allele with an in-frame duplication of 21 nucleotides in exon 7 (c.543_563dup), leading to the insertion of seven amino acids (QDVSMRR). Flow cytometric testing of native red blood cells (RBCs) showed very weak A antigen expression. This was in accordance with the enzyme activity test. CONCLUSION: In summary, we describe a novel A allele with a duplication of 21 nucleotides in exon 7 that significantly decreases the enzyme activity and leads to very weak expression of A antigen. (200 words).

Urine neutrophil gelatinase-associated lipocalin and urine output as predictors of the successful discontinuation of continuous renal replacement therapy in critically ill patients with acute kidney injury.

BACKGROUND: Continuous renal replacement therapy (CCRT) is a frequently used modality for the support of intensive care patients with acute kidney injury (AKI). Nevertheless, there are no objective criteria for the discontinuation of CRRT. The purpose of this study was to investigate whether urine neutrophil gelatinase-associated lipocalin (uNGAL) alone or in combination with urine output could be used as a diagnostic test for renal function recovery in ICU patients on CRRT. METHODS: This was a single-centre prospective observational study including patients with acute kidney failure needing CRRT. Sixty-nine patients were enrolled, and 54 completed the study. Of the 54 patients, 22 recovered renal function (REC), defined as dialysis independency at 72 h from discontinuation, while 32 patients did not (NREC). Urine NGAL was measured at 0, 6, 12, and 24 h after CRRT discontinuation. The cumulated urine output was measured for 24 h prior to discontinuation and at 6, 12, and 24 h after discontinuation. Missing uNGAL values were calculated by interpolation. The Youden's index was used to calculate cut-off values in order to define uNGAL and urine output single variable and 2-variable diagnostic tests with the optimum prediction of successful CRRT discontinuation. RESULTS: Baseline characteristics at CRRT initiation were similar between groups. Compared to the NREC group, the REC group had significantly higher urine output (p < 0.0001) and lower uNGAL (p < 0.001) at all time points, except for uNGAL at 24 h (p < 0.24). The best uNGAL predictor for successful CRRT discontinuation was uNGAL at 6 h after discontinuation (predictive value 80%). The best single predictor was cumulated urine output 24 h before discontinuation (predictive value 85%). The combinations of uNGAL at 6 h (cut-off 1650 µg/L) with cumulated urine output 24 h prior to discontinuation (cut-off 210 ml) proved to be the superior tests (using either "or" or "and"), with predictive values of 93% (successful CRRT discontinuation) and 92% (dialysis dependency). CONCLUSIONS: With a predictive value of 93%, the combination of uNGAL at 6 h after and the cumulated urine output 24 h prior to CRRT cessation proved to be the best diagnostic test for successful CRRT discontinuation in ICU patients. CLINICAL TRIAL REGISTRATION: N/A.

Performance characteristics of thromboelastometry assays using incompletely filled and prolonged stored samples.

BACKGROUND: Thromboelastometry (TEM) is often used to guide transfusion therapy in patients with massive bleeding. The effect of testing incompletely filled samples and those stored for a prolonged time at 4°C was investigated. METHODS: Whole blood samples were collected from 15 healthy blood donors and were pooled according to ABO group. From these pools, aliquots were taken and diluted to produce final whole blood:citrate buffer ratios ranging from 90:10 (fully filled sample) to 40:60 (extremely under filled samples). These samples were then tested by EXTEM, INTEM, and FIBTEM on calibrated ROTEM delta machines. Separately, the four samples at 90:10 dilution were kept at 4°C for 16-20 hours and then retested on the ROTEM machines. RESULTS: All of the samples at the 90:10 and 80:20 (half-filled sample) whole blood:citrate buffer dilutions demonstrated ROTEM parameters within their respective reference ranges, although the samples from the 80:20 dilution tended to demonstrate slightly longer or slower times, depending on each ROTEM parameter, compared to the completely filled samples. All of the samples with more dilute whole blood to citrate buffer ratios (i.e., 70:30 to 40:60) yielded abnormal TEM results. The TEM results for the 90:10 dilution samples exposed to 16-20 hours of storage at 4°C were within the reference intervals. CONCLUSION: Completely and half-filled samples, and completely filled samples after prolonged cold storage, produced normal ROTEM results. Tubes that are less than half-filled should not be used for ROTEM testing.

The quest for ingested peanut protein in human serum.

BACKGROUND: There is mounting evidence that systemic uptake of food allergens is key to triggering anaphylaxis. However, direct proof for this theory is still lacking. The purpose of this study was to quantify the absorption and to determine the absorption kinetics of immunoreactive peanut protein in relation to the allergic response in human. METHODS: Quantitative protein assays including mass spectrometry, dot blots and Western blotting were developed to determine the level of Ara h 2 absorption in human serum. The double monoclonal sandwich ELISA was applied to quantify absorbed Ara h 2 and 6, and the basophil histamine release assay and the human passive cutaneous anaphylaxis test were utilized to study the absorption kinetics of immunologically intact peanut proteins. RESULTS: The protein assays worked but were not sensitive enough to trace the minute amounts of absorbed Ara h 2 in human serum. The level of Ara h 6 in serum was found to be up to 0.2 ng/mL, but Ara h 2 could not be detected with the ELISA. Both the in vivo and the in vitro methods were successful in demonstrating that: immunoreactive peanut protein was absorbed shortly after ingestion (≤5 minutes); the peanut protein concentration peaks between 1 and 4 hours; and peanut proteins can circulate for at least 48 hours in the bloodstream. CONCLUSION: Ingested peanut protein is absorbed systemically and retains its immunoreactive capacity in human serum. However, the precise quantities and the implication for the elicitation of anaphylaxis remains to be elucidated.

[Complete tachyphylaxis for vasopressin in a patient with subarachnoid haemorrhage].

In this case report, we present a 28-year-old woman who was admitted to a neuro-intensive care unit with sub-arachnoid haemorrhage. She was intubated and haemodynamically unstable. Over five days the need for norepinephrine reached the level of 1.2 µg/kg/min to insure a sufficient cerebral perfusion pressure. Epinephrine and vasopressin were without effect in raising the blood pressure. On suspicion of tachyphylaxis the norepinephrine infusion was stopped, and no decline in blood pressure was observed. After two days without use of any vasopressor agents, the efficacy of norepinephrine returned to normal.

Increased but stable isoagglutinin titers in hemodialysis patients.

BACKGROUND: Prior to an ABO incompatible kidney transplantation it is important to know the recipient's pre-transplantation anti-A and/or anti-B (isoagglutinin) titer. This study determined if pre-transplantation isoagglutinin titers remained stable, over a period of 1 year, among hemodialysis patients. METHOD: Blood was collected four times, every 3 months from 54 hemodialysis patients (hemodialysed trice per week ≥ 6 months), and 56 healthy volunteers. Measurement of anti-A and anti-B (IgM and IgG) titers were performed on an automated solid phase analyzer. The titers were converted to log2 titer steps (e.g., titer 32 = titer step 5). RESULTS: Within blood group O, mean IgG anti-A and anti-B titers were significantly higher in the hemodialysis patients (n = 22, mean titer step: anti-A: 6.4 and anti-B:4.9), compared to the healthy volunteers [n = 19, mean titer step: anti-A: 4.9 and anti-B:3.5, p = 0.02 (anti-A) and p = 0.03 (anti-B)], despite blood group O hemodialysis patients having significantly lower total plasma IgG levels (median 8.1 g/L) than healthy volunteers (11.1 g/L, p = 0.001). Neither age, nor gender determined IgG anti-A or anti-B titers. In hemodialysis patients and healthy volunteers, the upper 95% confidence limit of anti-A and anti-B titer variation (IgM and IgG) during 1 year, did not exceed 1.0 titer step in any of the ABO groups. CONCLUSIONS: Anti-A and -B titers (IgM and IgG) remained stable in both the hemodialysis patients and healthy volunteers over a period of approximately 1 year. Blood group O hemodialysis patients had, despite lower total IgG levels, significantly elevated IgG anti-A and -B titers.

The effects of storage on platelet function in different blood products.

OBJECTIVES: Reduced platelet (PLT) function during storage has been shown for buffy-coat-derived platelet concentrates (BCP) and apheresis platelet units (AP), while for whole blood (WB) it has not been well studied. The aim of this study was to investigate PLT function in these blood products throughout storage using a novel flow cytometric assay. METHODS: Flow cytometric measurement of agonist-induced platelet aggregation, CD62P expression and PAC-1 binding during storage in BCP, AP (1-9 days at 20°C) and WB (1-21 days at 2-6°C). RESULTS: PLT-aggregation capacity decreased from day 1 to day 7 for almost all product-agonist combinations (P = .004 to P = .029) with aggregation capacity of WB being similar to that of AP and BCP. WB aggregation capacity remained relatively unchanged from day 7 to day 21. For all blood products, the fraction of agonist-induced CD62P-expression remained high and the fraction of PAC-1 binding decreased during storage. WB PLTs underwent only small changes in CD62P expression and PAC-1 binding from day 7 to day 21. CONCLUSION: This study found PLT aggregation in WB stored at 4°C to be as least as good as for BCP and AP stored at 20°C. WB retained significant PLT-aggregation capacity to day 21.

Results of noninvasive prenatal RHD testing in Gestation Week 25 are not affected by maternal body mass index.

BACKGROUND: Reliability of noninvasive prenatal RHD genotype test (NIP RHD) depends on having sufficient amounts of cell-free fetal DNA (cffDNA) in the maternal plasma sample. The fraction of cffDNA in maternal plasma is inversely related to maternal body mass index (BMI), suggesting that high maternal BMI may limit the test's accuracy. This study determined the effect of maternal BMI on the accuracy of NIP RHD. STUDY DESIGN AND METHODS: Results from NIP RHD performed in Gestation Week 25 were correlated to maternal BMI in Week 12. The accuracy of NIP RHD result was determined by correlation with serologic RhD types of the neonates. RESULTS: A total of 1618 pregnancies in 1588 D- women were included. Median BMI in these pregnancies was 24.2 (10%-90%, 20.1-32.4), and in 261 of 1618 (16%) pregnancies BMI was 30 or more (median BMI in this group was 33.6; 10th-90th percentiles, 30.5-41.1). NIP RHD was positive in 987 of 1618 (61%), negative in 582 of 1618 (36%), and inconclusive in 49 of 1618 (3.0%). Compared to the neonate's serologic RhD type, nine of 987 (0.9%) positive NIP RHD results were false positive, and four of 582 (0.7%) negative NIP RHD results were false negative (FN). In five of 49 (10%) inconclusive NIP RHD results, the neonatal RhD type was positive. There was no difference in median BMI between individuals who tested inconclusive or FN compared to those with true positive or true negative results (p = 0.80). CONCLUSION: The accuracy of NIP RHD testing performed in Gestation Week 25 does not depend on maternal BMI in the 12th gestation week.

Reduced platelet activation and platelet aggregation in patients with alcoholic liver cirrhosis.

Results from previous studies regarding platelet function in liver cirrhosis are discordant. The aim was to investigate platelet activation and platelet aggregation in patients with alcoholic liver cirrhosis. We included 27 patients with alcoholic liver cirrhosis and 22 healthy individuals. A recently established flow cytometric approach was used to measure platelet activation and platelet aggregation independent of sample platelet count. Platelet aggregation was further investigated using light transmission aggregometry (LTA) (for platelet count >100 × 109/L). Platelet agonists were adenosine diphosphate, thrombin receptor-activating peptide, arachidonic acid, collagen, and collagen-related peptide. Patients had lower median platelet count than healthy individuals, 125 × 109/L (interquartile range [IQR] 90-185) versus 240 × 109 (IQR 204-285), p < 0.001. Platelet activation levels in stimulated samples were lower in patients versus healthy individuals, e.g., after collagen-related peptide stimulation, the median percentage of platelets positive for activated glycoprotein IIb/IIIa was 85% (IQR 70-94) in patients versus 97% (IQR 94-99) in healthy individuals, p < 0.001; lower platelet activation capacity being associated with low platelet count and Child-Pugh class B/C cirrhosis. Flow cytometric platelet aggregation was reduced in patients for collagen-related peptide and for adenosine diphosphate, e.g., platelet aggregation (mean ± standard deviation) was 57% ± 4 in patients versus 70% ± 1 in healthy individuals for collagen-related peptide, p = 0.01. Light LTA showed reduced collagen-induced platelet aggregation in some patients compared with healthy individuals. In conclusion, platelet function was reduced in some patients with alcoholic liver cirrhosis and the severity was associated with platelet count and severity of liver cirrhosis.

An international investigation into O red blood cell unit administration in hospitals: the GRoup O Utilization Patterns (GROUP) study.

BACKGROUND: Transfusion of group O blood to non-O recipients, or transfusion of D- blood to D+ recipients, can result in shortages of group O or D- blood, respectively. This study investigated RBC utilization patterns at hospitals around the world and explored the context and policies that guide ABO blood group and D type selection practices. STUDY DESIGN AND METHODS: This was a retrospective study on transfusion data from the 2013 calendar year. This study included a survey component that asked about hospital RBC selection and transfusion practices and a data collection component where participants submitted information on RBC unit disposition including blood group and D type of unit and recipient. Units administered to recipients of unknown ABO or D group were excluded. RESULTS: Thirty-eight hospitals in 11 countries responded to the survey, 30 of which provided specific RBC unit disposition data. Overall, 11.1% (21,235/191,397) of group O units were transfused to non-O recipients; 22.6% (8777/38,911) of group O D- RBC units were transfused to O D+ recipients, and 43.2% (16,800/38,911) of group O D- RBC units were transfused to recipients that were not group O D-. Disposition of units and hospital transfusion policy varied within and across hospitals of different sizes, with transfusion of group O D- units to non-group O D- patients ranging from 0% to 33%. CONCLUSION: A significant proportion of group O and D- RBC units were transfused to compatible, nonidentical recipients, although the frequency of this practice varied across sites.