Viscoelastic Signals for Optimal Resuscitation in Trauma: Kaolin Thrombelastography Cutoffs for Diagnosing Hypofibrinogenemia (VISOR Study)
Authors: Chow Jonathan H. , Richards Justin E. , Morrison Jonathan J. , Galvagno Samuel M. , Tanaka Kenichi A. , Madurska Marta J. , Rock Peter , Scalea Thomas M. , Mazzeffi Michael A. 
Published: July 2019

BACKGROUND:
Acute traumatic coagulopathy is common in trauma patients. Prompt diagnosis of hypofibrinogenemia allows for early treatment with cryoprecipitate or fibrinogen concentrate. At present, optimal cutoffs for diagnosing hypofibrinogenemia with kaolin thrombelastography (TEG) have not been established. We hypothesized that kaolin kaolin-TEG parameters, such as kinetic time (K-time), α-angle, and maximum amplitude (MA), would accurately diagnose hypofibrinogenemia (fibrinogen <200 mg/dL) and severe hypofibrinogenemia (fibrinogen <100 mg/dL).

METHODS:
Adult trauma patients (injury severity score >15) presenting to our trauma center between October 2015 and October 2017 were identified retrospectively. All patients had a traditional plasma fibrinogen measurement and kaolin-TEG performed within 15 minutes of each other and within 1 hour of admission. Some patients had additional measurements after. Receiver operating characteristic (ROC) curve analysis was performed to evaluate whether K-time, α-angle, and MA could diagnose hypofibrinogenemia and severe hypofibrinogenemia. Area under the ROC curve (AUROC) was calculated for each TEG parameter with a bootstrapped 99% confidence interval (CI). Further, ROC analysis was used to estimate ideal cutoffs for diagnosing hypofibrinogenemia and severe hypofibrinogenemia by maximizing sensitivity and specificity. In addition, likelihood ratios were also calculated for different TEG variable cutoffs to diagnose hypofibrinogenemia and severe hypofibrinogenemia.

RESULTS:
Seven hundred twenty-two pairs of TEGs and traditional plasma fibrinogen measurements were performed in 623 patients with 99 patients having additional pairs of tests after the first hour. MA (AUROC = 0.84) and K-time (AUROC = 0.83) better diagnosed hypofibrinogenemia than α-angle (AUROC = 0.8; P = .03 and P < .001 for AUROC comparisons, respectively). AUROCs statistically improved for each parameter when severe hypofibrinogenemia was modeled as the outcome (P < .001). No differences were found between parameters for diagnosing severe hypofibrinogenemia (P > .05 for all comparisons). The estimated optimal cutoffs for diagnosing hypofibrinogenemia were 1.5 minutes for K-time (95% CI, 1.4–1.6), 70.0° for α-angle (95% CI, 69.8–71.0), and 60.9 mm for MA (95% CI, 59.2–61.8). The estimated optimal cutoffs for diagnosing severe hypofibrinogenemia were 2.4 minutes for K-time (95% CI, 1.7–2.8), 60.6° for α-angle (95% CI, 57.2–67.3), and 51.2 mm for MA (95% CI, 49.0–56.2). Currently recommended K-time and α-angle cutoffs from the American College of Surgeons had low sensitivity for diagnosing hypofibrinogenemia (3%–29%), but sensitivity improved to 74% when using optimal cutoffs.

CONCLUSIONS:
Kaolin-TEG parameters can accurately diagnose hypofibrinogenemia and severe hypofibrinogenemia in trauma patients. Currently recommended cutoffs for the treatment of hypofibrinogenemia are skewed toward high specificity and low sensitivity. Many patients are likely to be undertreated for hypofibrinogenemia using current national guidelines.