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2019 AAST PODIUM

Plasmin thrombelastography rapidly identifies trauma patients at risk for massive transfusion, mortality, and hyperfibrinolysis: A diagnostic tool to resolve an international debate on tranexamic acid?

Barrett, Christopher D. MD; Moore, Hunter B. MD, PhD; Vigneshwar, Navin MD; Dhara, Sanjeev BS; Chandler, James BA; Chapman, Michael P. MD; Sauaia, Angela MD, PhD; Moore, Ernest E. MD; Yaffe, Michael B. MD, PhD

Author Information
Journal of Trauma and Acute Care Surgery: December 2020 - Volume 89 - Issue 6 - p 991-998
doi: 10.1097/TA.0000000000002941
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Abstract

A spectrum of fibrinolysis phenotypes exist in trauma patients, where the prevalence of hyperfibrinolysis in severely injured trauma patients (Injury Severity Score [ISS], >15) is roughly 20% and carries a greater than threefold increased risk of mortality that is primarily due to bleeding.1–4 Tranexamic acid (TXA), an antifibrinolytic drug used to treat bleeding in trauma patients, demonstrated a modest survival benefit in the largest randomized controlled trial to date (Clinical Randomization of an Antifibrinolytic in Significant Haemorrhage 2 [CRASH-2]), but decisions to administer TXA in this trial were not based on patients' fibrinolysis phenotypes and have not been without controversy.5,6 Beyond not dosing TXA based on fibrinolysis phenotypes, other common criticisms of CRASH-2 include that it was conducted primarily in developing countries with poorly developed trauma systems and low penetrating injury rates that are dissimilar from the trauma encountered in urban environments and developed trauma systems, and importantly showed no reductions in blood transfusion requirements.7 While a subsequent study (MATTERs [Military Application of Tranexamic Acid in Trauma Emergency Resuscitation]) had far more impressive results with respect to mortality benefit from TXA on primarily penetrating and severely injured patients in a combat environment,8 it was a retrospective study, and other high-acuity retrospective analyses such as the propensity-matched analysis by Valle et al.6 in a large urban US trauma center actually found that those who got TXA required more blood products and had higher mortality.

In a recent study by Moore et al.,9 trauma patients with hyperfibrinolysis and depletion of fibrinolytic inhibitors (DFIs) measured by thrombelastography (TEG) showed improved clot strength following TXA administration, but this study and others have also shown harmful effects from TXA administered to patients without hyperfibrinolysis including an increased incidence of VTE, organ failure, and mortality.9–13 Given these study results and others, a case has been made for selective TXA use based on patients' fibrinolysis phenotypes with the rationale that targeted TXA administration would maximize its mortality benefit.14

A significant clinical challenge to implementing targeted TXA administration is the ability to rapidly distinguish which trauma patients are hyperfibrinolytic, as the CRASH-2 data clearly showed that the mortality benefit from TXA is greatest when given early, where, for every 15 minutes elapsed that TXA was not given, there was a 10% reduction in efficacy and mortality actually increased if dosed after 3 hours.15,16 The viscoelastic assays used clinically to diagnose hyperfibrinolysis, such as TEG, typically take close to 1 hour to obtain results,17,18 and this delay represents significant lost time before TXA administration that reduces its efficacy.16 We therefore set out to develop a TEG-based assay that could more rapidly identify patients at highest risk of bleeding and death who either have, or are at significant risk for, hyperfibrinolysis while also identifying those unlikely to have hyperfibrinolysis to help guide rapid TXA administration decisions.

The assay we developed, the plasmin TEG (P-TEG), is based on the rationale that addition of exogenous plasmin to citrated whole blood causes a shortening of reaction time (R time) in healthy volunteers19 (i.e., the time it takes for enough clot to form on TEG that it becomes a detectable signal), likely via factor V activation.20 In addition, this exogenous plasmin rapidly complexes with and depletes the main plasmin inhibitor α-2 antiplasmin (α2AP) from the whole blood solution with a half-life of 100 ms.21 Thus, beyond shortening the R time in healthy/nonhyperfibrinolytic states,19 exogenous plasmin addition could potentially unmask underlying hyperfibrinolysis phenotypes in trauma patients known to be driven by tissue plasminogen activator (tPA)22,23 by removing terminal inhibition of the fibrinolysis pathway from residual α2AP. Similarly, in patients who already have DFIs from prior activation of fibrinolysis, which may or may not still be ongoing, plasmin addition may cause direct and unopposed fibrinolysis. In these scenarios (hyperfibrinolysis and/or DFI), exogenous plasmin is expected to cause a paradoxical prolongation of the R time on P-TEG relative to the corresponding citrate native TEG via early onset of fibrinolysis while the clot is still forming. We sought to take advantage of this potential shift in R time and hypothesized that a shortening of the P-TEG R time (P-TEG R time < native TEG R time) would be observed in nonhyperfibrinolytic states (i.e., ratio of R times is <1),19 whereas a relative prolongation of the R time would be observed on P-TEG (P-TEG R time ≥ native TEG R time, from here forward P-TEG positive) in hyperfibrinolytic and similar high-risk states including DFI (i.e., ratio of R times is ≥1). We further hypothesized that trauma patients who are P-TEG positive have a high rate of massive transfusion (MT) and mortality. Because citrate native TEG R time is typically available within 10 minutes, the P-TEG assay may potentially provide an expedited, dichotomous, and user-friendly readout to stratify which trauma patients are highest risk for bleeding, hyperfibrinolysis, and death and may therefore benefit most from TXA.

PATIENTS AND METHODS

Human Subjects

Blood collection and study assays were performed and analyzed on a sample of adult trauma patients (≥18 years old) included from 12 months ending November 2019 in our Trauma Activation Patient (TAP) study, which includes all trauma activation patients who sustained blunt or penetrating trauma at the Ernest E. Moore Shock Trauma Center at Denver Health, an American College of Surgeons–verified and Colorado state–certified, academic, level 1 trauma center. The TAP study was approved by the Colorado Multiple Institution Review Board (COMIRB number 13-3087) and performed under waiver of consent. Criteria for inclusion in TAP are adult patients (≥18 years old) who presented as trauma activations, either by ground or air transport from the scene of injury, an emergency department (ED) walk-in, or nontransfer patients upgraded to a trauma activation on arrival. The criteria are traumatic injury with any of the following: (1) Glasgow Coma Scale score of <8 with presumed thoracic, abdominal, or pelvic injury; (2) respiratory compromise, obstruction, and/or intubation with presumed thoracic, abdominal, or pelvic injury; (3) blunt trauma with systolic blood pressure of <90 mm Hg; (4) mechanically unstable pelvic injury; (5) penetrating injuries with injury to neck and/or torso with systolic blood pressure of <90 mm Hg, gunshot wound penetrating the neck/torso, or stab wounds to the neck/torso that require endotracheal intubation; (6) amputation proximal to the ankle or wrist; or (7) the emergency medicine attending or chief surgical resident suspects that the patient is likely to require urgent operative intervention. Exclusion criteria were as follows: age younger than 18 years, patients whose initial blood sample was not collected within 1 hour postinjury, infusion of blood products before the collection of blood samples, patients presenting as consultations from external hospitals, documented chronic liver disease (total bilirubin, >2.0 mg/dL) or advanced cirrhosis discovered on laparotomy, known inherited defects of coagulation function (e.g., hemophilia or von Willebrand disease), patients found to be on anticoagulants at the time of their injury, subsequent downgrades from trauma activation to trauma alert or nontrauma status in the ED, and patients who were pregnant or prisoners. Patients were removed from the study if any of these criteria became known after activation.

Blood Collection

Blood was collected in 3.5-mL tubes containing 3.2% citrate in the prehospital ambulance or upon arrival to the ED. Professional research assistants performed coagulation assays within 2 hours of blood draw on eligible patients. Additional assays were ordered at the discretion of the treating surgeon and performed by the hospital laboratory.

Viscoelastic and Coagulation Assays

All assays were conducted by a team of trained professional research assistants with extensive experience performing TEG and coagulation assays. Citrated blood samples were analyzed using the TEG 5000 Thrombelastography Hemostasis Analyzer (Haemonetics Corporation, Braintree, MA). The following indices were obtained from the tracings of the TEG: R time (minutes), angle (°), maximum amplitude (MA; mm), and clot lysis 30 minutes after MA (LY30; %). Similarly, coagulation assays including international normalized ratio, D-dimer levels, and fibrinogen levels were measured on citrated platelet poor plasma as previously described (Diagnostica Stago Inc., Parsippany, NJ).24

Rapid TEG (rTEG; kaolin and tissue factor activated TEG) and native TEG (no activator) were conducted according to manufacturer recommendations. An additional previously published18 modified assay to quantify sensitivity to fibrinolysis was done in parallel, termed tPA Challenged TEG. In brief, 500 μL of citrated whole blood was pipetted into a customized vial containing lyophilized tPA (Thrombo Therapeutics Inc., Walpole, MA) to a final concentration of 75 ng/mL of tPA for assays reporting LY30 and DFI and 150 ng/mL of tPA for time to maximum amplitude (TMA) assays, and mixed by gentle inversion. A 340-μL aliquot of this mixture was then transferred to a 37°C TEG cup, preloaded with 20 μL of 0.2 mol/L CaCl2 without tissue factor or kaolin activator.

Similarly and also in parallel, our novel modified TEG assay, P-TEG, was performed by adding 16.6 μg of exogenous active human plasmin (Haematologic Technologies, Inc., Essex, VT) to 500 μL of trauma patient citrated whole blood (final plasmin concentration, 32.2 μg/mL) to cause an estimated 40% depletion of plasmin's primary inhibitor α2AP, and a 340-μL aliquot of this mixture was then transferred to a 37°C TEG cup preloaded with 20 μL of 0.2 mol/L CaCl2 without tissue factor or kaolin activator. The P-TEG was considered positive (P-TEG positive) when the P-TEG R time is greater than or equal to native TEG R time.

Definitions of Fibrinolysis Variables and MT

Hyperfibrinolysis was defined for analytic purposes according to two previously published thresholds including LY30 of ≥3%2,25 and LY30 of ≥7.6%26 (and manufacturer recommended reference range) on rTEG. Risk for MT was then compared between other published methods of MT prediction and P-TEG including (1) the TMA on tPA TEG ≤15 minutes,18 (2) DFIs defined as tPA TEG LY30 >42%,9 and (3) rTEG LY30 values and composite scores. Massive transfusion was defined as >4 U of red blood cells transfused per hour any time during the first 6 hours or death before this time.18,27

Extrapolated Patient Population to Explore Role of P-TEG for Targeted TXA Use

A previously described trauma population of 630 trauma patients with comprehensive TEG data was analyzed to determine the protective versus harmful effects of TXA on patients who underwent an MT.9 Patients likely to benefit from TXA were identified as patients both having hyperfibrinolysis on rTEG and having DFIs (as defined previously).9 These patients were considered “on target” for TXA use based on an improvement in fibrin clot strength with TXA, while “off target” for TXA use was patients who did not meet these criteria and were previously published to have increased mortality if administered TXA.9 The theoretic timing of the decision to use TXA was based on the time to results of P-TEG as well as tPA TEG TMA and the LY30 of the other relevant TEGs. Speculative survival benefit or harm was estimated based on the percent change in survival between patients who underwent an MT with on-target TXA use versus off-target TXA use, expressed as fold change in survival or death.

Statistical Analysis

SPSS version 23 (IBM, Armonk, NY) and Prism version 8.3.1 (GraphPad, San Diego, CA) were used for statistical analyses. Clinical and TEG measurements are presented as median and interquartile range (IQR; 25th–75th percentile) or n (%). Receiver operating characteristic curves using all of the specified assay parameters by themselves and in the combinations described were generated. Categorical variables were compared by χ2 test, and a Mann-Whitney U test was used for comparison of continuous variables. Significance (α) was set to the 0.05 level.

RESULTS

Patient Population

For 12 months, 167 patients underwent P-TEGs. Fifteen patients were excluded from analysis because of incomplete TEG assays (4 rTEG assays, 5 citrated native TEG assays, 10 tPA TEG assays). Of the 148 patients remaining, the median age was 35 years with a range of 18 to 90, the majority (77%) of patients were male, and 45% sustained penetrating injuries. The median ISS was 20 (IQR, 9–30). The MT rate in this group was 10% with an overall 30-day mortality rate of 18.9% (Table 1).

TABLE 1 - Trauma Patient Characteristics (N = 148)
Variable n (%) or Median (Range or IQR)
Age 35 (range, 18–90)
Male 114 (77)
ISS 20 (IQR, 9–30)
AIS head/neck 0 (IQR, 0–4)
AIS chest 0 (IQR, 0–3)
AIS abdomen/pelvis 0 (IQR, 0–2)
AIS extremities 0 (IQR, 0–2)
AIS head/neck, mean ± SD 1.9 (2.1)
AIS chest, mean ± SD 1.5 (1.7)
AIS abdomen/pelvis, mean ± SD 1.0 (1.5)
AIS extremities, mean ± SD 1.0 (1.5)
Penetrating injury 67 (45)
MT 15 (10)
Mortality at 24 h 15 (10)
Mortality at 30 d 28 (18.9)
AIS, Abbreviated Injury Scale.

P-TEG and Time to Assay Results

Plasmin TEG assays obtained results significantly faster than all other comparison assays with a median time to positive results of 4.7 minutes, which was more than 11-fold faster than the rTEG LY30 median time to assay results of 54.2 minutes (p < 0.001) and approximately 3-fold faster than the tPA TEG TMA median positive assay time of 12.7 minutes (p < 0.001) (Table 2). Positive P-TEG assays occurred in 13.5% of patients (examples shown in Fig. 1). There were no significant differences between P-TEG positive and P-TEG negative patients with respect to age, sex, ISS, or mechanism of injury (blunt vs. penetrating), and while there was not a significant difference in Abbreviated Injury Scale head/neck scores between the two groups, there was a significantly lower median Glasgow Coma Scale score in the P-TEG positive group (Table 3). The rate of MT was greater than fourfold higher in P-TEG positive patients compared with P-TEG negative patients (30% vs. 7%; p = 0.0015). Patients who were P-TEG positive had a greater than fourfold higher mortality at 24 hours (33.3% vs. 7.8%; p = 0.0177) and greater than twofold higher mortality at 30 days (35% vs. 16.4%; p = 0.0483). Patients who were both P-TEG positive and tPA TEG TMA positive had a 50% MT rate and 83% mortality, compared with a 2.4% MT rate (20-fold lower) and 12.9% mortality (>6-fold lower) if both tests were negative.

TABLE 2 - Time to Assay Results
Variable Median Time to Result (IQR), min p
P-TEG positive 4.7 (2.5–9.1)
tPA TEG TMA positive 12.7 (9.2–13.8) <0.001
tPA TEG LY30 47.1 (42.6–51.2) <0.001
rTEG LY30 54.2 (51.1–58.1) <0.001

Figure 1
Figure 1:
Demonstrative examples of three negative P-TEGs and three positive P-TEGs. (A), Three examples of R time on P-TEG being shorter than R time on their corresponding citrate native TEG, which is considered a negative P-TEG. (B), Three examples of R time on P-TEG being longer than R time on their corresponding citrate native TEG, which is considered a positive P-TEG.
TABLE 3 - Clinical Data and Outcomes Based on P-TEG Results
n (%) or Median (IQR)
Variable P-TEG Negative P-TEG Positive p
Total no. patients = 148 n = 128 (86.5) n = 20 (13.5)
Female (n = 34, 23.0%) 29 (85.3) 5 (14.7) 0.8168
Age 34 (26–48) 41 (28–54) 0.3194
ISS 19.0 (9–29.0) 24.0 (10.0–43.0) 0.1869
AIS head neck 0.0 (0.0–4.0) 2.0 (0.0–5.0) 0.3807
AIS chest 0.0 (0.0–3.0) 3.0 (2.0–3.0) 0.005
AIS abdomen pelvis 0.0 (0.0–2.0) 0.0 (0.0–2.0) 0.5877
AIS extremities 0.0 (0.0–2.0) 0.0 (0.0–2.0) 0.7472
Blunt injury 69 (53.9) 12 (60.0) 0.6106
ED GCS 14.0 (7.0–15.0) 7.0 (3.0–14.5) 0.0386
Prehospital SBP 110.0 (86.0–140.0) 86.0 (30.0–123.0) 0.0338
Prehospital HR 100.0 (82.0–120.0) 105.0 (60.0–120.0) 0.7687
ED SBP 121.5 (101.0–140.0) 81.0 (0.0–126.5) 0.0075
ED HR 100.0 (77.0–117.0) 96.0 (9.0–112.5) 0.2409
ED shock index 0.8 (0.7–1.0) 1.0 (0.1–1.4) 0.1792
pH 7.315 (7.25–7.38) 7.25 (7.1–7.335) 0.0117
Base excess, mEq/L −6.2 (−10.1 to −3.5) −9.6 (−18.5 to −6.9) 0.0239
Lactate, mmol/L 3.8 (2.9–7.2) 2.6 (2.2–7.3) 0.3345
Fibrinogen, mg/dL 225 (187–294) 153 (134–219) 0.0435
Hgb, g/dL 13.9 (12.7–15.7) 13.5 (11.2–15.3) 0.1238
Platelet count/mm3 266 (198–325) 225 (176–315) 0.207
D-dimer, μg/mL 3.3 (0.7–15.5) 19.9 (1.4–20) 0.1446
INR 1.2 (1.1–1.3) 1.4 (1.2–1.9) 0.0025
DFIs (tPA TEG LY30 >42%) 23 (17.97) 11 (55.0) 0.0008
tPA TEG TMA 20.7 (17.8–23.7) 16.1 (9.2–23) 0.0097
tPA TEG LY30 48.4 (30.4–60.4) 73.5 (33.8–88.1) 0.007
Hyperfibrinolysis (rTEG LY30 ≥7.6%) 11 (8.59) 5 (25.0) 0.0441
Hyperfibrinolysis (rTEG LY30 ≥3%) 22 (17.2) 5 (25.0) 0.4002
rTEG LY30 1.2 (0.6–2.0) 1.5 (0.3–8.5) 0.8377
cnTEG LY30 1.2 (0.4–2.3) 1.7 (0.6–15.5) 0.0387
RBC at 6 h, U 0.0 (0.0–4.0) 3.5 (0.0–6.0) 0.0524
FFP at 6 h, U 0.0 (0.0–2.0) 2.0 (0.0–4.5) 0.1093
Platelets at 6 h, U 0.0 (0.0–0.0) 0.0 (0.0–0.5) 0.6396
MT 9 (7.0) 6 (30.0) 0.0015
Mortality at 24 h 10 (7.81) 5 (33.33) 0.0177
Mortality at 30 d 21 (16.4) 7 (35.0) 0.0483
cnTEG, citrated native TEG; FFP, fresh frozen plasma; GCS, Glasgow Coma Scale; Hgb, hemoglobin; HR, heart rate; INR, international normalized ratio; RBC, red blood cell; SBP, systolic blood pressure.

Fibrinolytic Profiles

Being P-TEG positive was significantly associated with having DFIs (55% vs. 18%; p = 0.0008), rTEG hyperfibrinolysis (higher-threshold definition, LY30 ≥7.6%) (p = 0.0441), a shorter tPA TEG TMA (16.1 vs. 20.7 minutes; p = 0.0097), and a higher tPA TEG LY30 (73.5% vs. 48.4%; p = 0.0070), but not the lower-threshold LY30 rTEG definition of hyperfibrinolysis (LY30 ≥3%) (p = 0.4002) (Table 3). Plasmin TEG–positive patients also had a significantly lower fibrinogen level upon arrival to the ED (153 vs. 225 mg/dL; p = 0.0435) and a trend toward higher D-dimer levels (19.9 vs. 3.3 μg/mL; p = 0.14). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for P-TEG and the composite of P-TEG with tPA TEG TMA for MT, low- and high-threshold definitions of rTEG hyperfibrinolysis, DFI, and on-target TXA (Table 4). Plasmin TEG performed best in relation to DFI with a PPV of 58% and NPV of 81%, where it outperformed the previously published9,18 shortened TMA on tPA TEG (PPV, 40%; NPV, 90%), and nearly all parameters improved when P-TEG was combined with tPA TEG TMA. Receiver operating characteristic curves for performance of each individual assay in identifying patients at risk for massive bleeding (MT) are depicted in Figure 2A along with their respective times to assay results relative to need for MT (Fig. 2B). Plasmin TEG had an area under the receiver operating characteristic curve (AUROC) for MT of 0.686 (95% confidence interval [CI], 0.51–0.862; p = 0.028), tPA TEG TMA had an AUROC of 0.776 (95% CI, 0.624–0.929; p = 0.001), and the composite of P-TEG and tPA TEG TMA had an AUROC of 0.811 (95% CI, 0.668–0.955; p < 0.001) for MT with these composite results being available in a median time of 12.7 minutes (IQR, 9.2–13.8 minutes). This composite of P-TEG and tPA TEG TMA outperformed rTEG LY30 ≥3% both in terms of AUROC for MT and time to results, which for rTEG LY30 ≥3% was 0.708 (95% CI, 0.538–0.878; p = 0.014) and 54.2 minutes (IQR, 51.1–58.1; p < 0.001). The AUROCs for each assay and composite of assays for predicting MT as a function of time to availability of results are shown in Figure 2C. Areas under the receiver operating characteristic curve were also calculated for predicting which patients were on target for TXA, where P-TEG had an AUROC of 0.643 (95% CI, 0.465–0.821; p = 0.09), tPA TEG TMA had an AUROC of 0.819 (95% CI, 0.681–0.957; p < 0.001), and a composite of P-TEG with tPA TEG TMA had an AUROC of 0.840 (95% CI, 0.719–0.962; p < 0.001).

TABLE 4 - Contingency Analysis of P-TEG and tPA TEG TMA
Variable Sensitivity Specificity PPV, % NPV, %
P-TEG MT 0.40 (0.20–0.64) 0.89 (0.83–0.94) 30 (15–52) 93 (87–96)
rTEG LY30 >3% 0.19 (0.08–0.37) 0.88 (0.81–0.92) 25 (11–47) 83 (75–88)
rTEG LY30 >7.6% 0.31 (0.14–0.56) 0.89 (0.82–0.93) 25 (11–47) 91 (85–95)
DFI 0.32 (0.19–0.49) 0.92 (0.86–0.96) 58 (36–77) 81 (73–87)
On-target for TXA 0.36 (0.16–0.61) 0.89 (0.82–0.93) 26 (12–49) 93 (87–96)
tPA TEG TMA MT 0.69 (0.42–0.87) 0.86 (0.79–0.91) 35 (19–54) 96 (91–99)
rTEG LY30 >3% 0.50 (0.31–0.69) 0.87 (0.79–0.92) 42 (26–0.61) 90 (83–94)
rTEG LY30 >7.6% 0.77 (0.50–0.92) 0.87 (0.80–0.92) 38 (22–57) 97 (92–99)
DFI 0.64 (0.47–0.78) 0.95 (0.89–0.98) 81 (62–91) 89 (82–94)
On-target for TXA 0.77 (0.50–0.92) 0.87 (0.80–0.92) 38 (22–57) 97 (92–99)

Figure 2
Figure 2:
Diagnostic assay performance and time to results for predicting MT. (A), The AUROC for predicting MT for P-TEG positive, tPA TEG TMA of ≤15 minutes, tPA TEG DFI (LY30 >42%), rTEG LY30 >3%, composite of P-TEG positive plus tPA TEG TMA ≤15 minutes, composite of P-TEG positive plus tPA TEG TMA ≤15 minutes plus tPA TEG DFI, and composite of P-TEG positive plus tPA TEG TMA ≤15 minutes plus tPA TEG DFI plus rTEG LY30 >3%. (B), Stratification of time to assay results relative to need for MT for P-TEG, tPA TEG TMA, tPA TEG LY30 (DFI is same by definition), and rTEG LY30 (median time ± IQR, in minutes). (C), The AUROC of assays for predicting MT as a function of time to obtain assay result (AUROC ± 95% CI).

Time to Assay Results and Speculative Decision for Selective TXA Use

Based on the mortality differences in a 630–trauma patient data set reported in Ref.9 that examined whether or not patients were on target for TXA (i.e., gained clot strength), extrapolated/speculative calculations were carried out for using P-TEG alone and in combination with other subsequently available assays to illustrate potential future utility of the assay. At 5 minutes, 36% of patients on target for TXA use could be captured by P-TEG while dosing TXA to 10% of all patients who were off target, which improves to capturing 84% of all patients considered on target by 12.7 minutes when used in tandem with tPA TEG TMA while only indicating TXA dosing to 19% of the patients who would be considered off target. Such an approach yields a theoretic threefold mortality benefit relative to nonselective TXA use and does so within the first defined 15-minute time increment of TXA benefit.15

DISCUSSION

Because trauma is the leading cause of death in working-age adults and noninfant children,28 and bleeding is the most common cause of preventable death, any improvement in survival after traumatic injury is noteworthy. While TXA use has led to an overall reduction in mortality of 1.5% (0.8% reduction in mortality due to bleeding) when dosed nonselectively to bleeding trauma patients in a large randomized controlled trial,5 a case has been made for selective use of TXA to maximize the benefits and minimize potential harms.12,14 Furthermore, early dosing of TXA is of paramount importance because efficacy is lost at a rate of 10% for every 15 minutes that goes by.15 As such, our group set out to generate better methods for rapidly stratifying which patients are most likely to benefit from TXA while minimizing potential harms based on previous work.9,10 Here we report our initial study findings using a novel assay, the P-TEG, which we developed to try to reduce the time required to identify trauma patients at high-risk for massive bleeding (MT), death, and risk for hyperfibrinolysis (i.e., have DFI and/or are actively hyperfibrinolytic) with the goal that this may help guide TXA dosing decisions in the future.

In this initial study, we found that P-TEG provides a rapid and dichotomous user-friendly readout in a median time to positive assay results of 4.7 minutes and added little-to-no additional prep time (under 1 minute) that is similar to what is done for running assays like rTEG that require mixing the blood with the activating reagent. Being P-TEG positive was associated with a greater than fourfold risk of MT, greater than fourfold risk of death at 24 hours, and greater than twofold risk of death at 30 days. Empirically, this bleeding group at high risk of death would likely obtain a greater benefit from TXA than the general trauma population. With specific respect to fibrinolysis, P-TEG seemed to be more strongly related to DFI than TEG measures of hyperfibrinolysis, with a strong statistical association with DFI (Table 3) and a PPV for DFI of 58%. While the specificity of P-TEG was good at around 90% for all primary outcome measures (MT, rTEG LY30, DFI, and on-target TXA use) and the NPVs of P-TEG were acceptable (81–93%), the P-TEG was limited in its PPV for hyperfibrinolysis as measured by rTEG (25% for both low- and high-threshold rTEG LY30 levels). This finding is somewhat peculiar, however, because, while not statistically significant, there was a trend toward a greater than sixfold elevation in D-dimer in patients who were P-TEG positive, which suggests that patients who were P-TEG positive but did not have hyperfibrinolysis defined by LY30 on rTEG were lysing clots at some point recently (if not ongoing) and may reflect a more recent report in the literature of ongoing “occult” fibrinolysis that is missed by viscoelastic lysis measures.29

We then evaluated P-TEG in combination with the tPA TEG TMA assay, which had a median time to positive results of 12.7 minutes and provided more powerful results while still falling within the first 15-minute time increment where TXA is known to be most beneficial.15 This composite of the two assays had an AUROC of 0.81 for MT and 0.84 for on-target TXA, with the sensitivities improving markedly across the board and the NPV for MT, hyperfibrinolysis, and DFI all being 90% or higher, and the NPV for on-target TXA use was excellent at 98%. This combination of the two assays in ≤15 minutes are theoretically able to capture as much as 84% of patients considered to be on target for TXA use while only indicating TXA dosing to 19% of the off-target population. This is a purely speculative calculation based on a previously published data set9 but serves to illustrate the point that this assay and approach is worthy of further study and refinement, particularly given that such a calculation indicates a theoretic threefold mortality benefit over nonselective dosing of TXA and does so within the first 15-minute time increment where TXA is of the most utility.

There are extensive arguments for and against selective dosing of TXA that are beyond the scope of this article to review comprehensively, but it is worth highlighting some of them here in the context of the current study. First, one powerful argument in favor of a nonselective approach is pragmatism, where the combination of timely administration for maximal efficacy and minimal confusion is appealing. Furthermore, it has been argued that TXA does not have any significant harmful consequences even in patients who are not hyperfibrinolytic.30 This is a point of contentious debate, as our group and others have reported harm including VTE and increased mortality (primarily from organ failure) when given to the wrong group of trauma patients.6,9–12 Another criticism to implementing selective use of TXA is that the viscoelastic assays typically used to diagnose hyperfibrinolysis take nearly an hour to provide a result, which is precious time given the 10% efficacy loss of TXA for every 15 minutes that go by.5,15,16 Such a delay in diagnosis may negate a substantial portion of the potential benefit of selective TXA dosing, but our position is that, in light of the development of faster surrogates for fibrinolysis such as the tPA TEG TMA18 and our current study reported here, such a time argument could be mitigated and become a nonissue with further refinement of these more rapid assays. Finally, feasibility has been argued to be potentially difficult given the multiple TEG assays required for our currently reported approach that requires running three TEG assays simultaneously (citrate native TEG, P-TEG, and a tPA TEG). While this is more logistically difficult on the older TEG 5000 that only has two channels per machine (i.e., requires two machines to perform all required assays), the new TEG 6S runs four assays per cartridge, so in these instruments, our approach could be done on a single customized cartridge, and similarly, the ROTEM Delta devices also have four channels, so again it only requires a single device. Overall, it is our position that there is ample evidence to question the nonselective approach to TXA dosing for trauma patients, even when considering the pragmatic arguments and inexpensive application of such an approach, as the proposed barriers to rapid and selective dosing seem to be readily surmountable and the potential benefit from the selective TXA approach is worthy of further pursuit and study.

There are several important limitations to our study. First, we did not actually use this novel diagnostic test to indicate therapy with TXA, so any benefit to using P-TEG results to guide TXA administration is based on both extrapolation and an assumption that higher rates of MT, mortality, and DFI in the P-TEG positive group likely renders them more likely to benefit from TXA. Second, our sample size was somewhat modest, so further data collection and study are warranted. In addition, it was done at a single institution, so validation across multiple institutions is needed. Furthermore, we have not explored the relationship of increasing (or decreasing) the ratio of P-TEG to native TEG R times to increase our sensitivity and evaluate the exact data cutoffs/metrics to maximize the diagnostic capabilities and benefit-to-harm ratio with this test, as it may be the case that using different R time ratios (e.g., 1.1 or 1.2) would improve its performance. Similarly, we have only tested and reported an isolated plasmin concentration for P-TEG that was chosen based on prior healthy volunteer studies,19 but the test may achieve markedly improved results at a more optimal yet currently undefined plasmin concentration and further study will be needed to explore this possibility. Finally, despite the user-friendly dichotomous readout of P-TEG, as with all advanced coagulation testing, this test may be difficult to implement outside of mature trauma systems and military applications given technical demands.

In summary, we have developed a novel modified diagnostic assay for use on currently available commercial equipment commonly used in trauma that can, in under 5 minutes, rapidly identify trauma patients at highest risk for MT (i.e., massive bleeding), death at both 24 hours and 30 days, and high risk for hyperfibrinolysis (DFI) and, potentially, with future improvements (with or without composite use of tPA TEG TMA), may be able to help guide selective TXA dosing. Further study with larger numbers across multiple institutions with additional analysis and refinement of the best way to use P-TEG is warranted.

AUTHORSHIP

C.D.B. and H.B.M. conceived the study. C.D.B., S.D., and J.C. performed the technical components of the study. C.D.B., H.B.M., N.V., E.E.M., M.P.C., A.S., and M.B.Y. performed data analysis and interpretation. C.D.B. and H.B.M. wrote the article, and E.E.M. and M.B.Y. edited the article.

DISCLOSURE

C.D.B., M.B.Y., E.E.M., H.B.M., and M.P.C. are cofounders of Thrombo Therapeutics, Inc. M.B.Y. holds stock options in Merrimack Pharmaceuticals. H.B.M., E.E.M., and M.P.C. have a patent pending related to the tPA-challenged TEG (US Patient Application 15/524,095). C.D.B., M.B.Y., E.E.M., and H.B.M. have a patent pending related to the P-TEG (US Patent Application 62/505,021). C.D.B., M.B.Y., E.E.M., H.B.M., and M.P.C. all receive research grant support from Haemonetics and Instrumentation Laboratories. C.D.B., M.B.Y., E.E.M., H.B.M., and A.S. all receive research grant support from Genentech. All other authors have nothing to disclose.

This work was supported by NIH grants UM1-HL120877 (M.B.Y., E.E.M.), F32-HL134244 (C.D.B.), and L30-GM120751 (C.D.B.) and DoD Peer Reviewed Medical Research Program, contract number W81XWH-16-1-0464 (M.B.Y.).

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Keywords:

Trauma; coagulation; fibrinolysis; hemorrhage; tranexamic acid

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