Hemoglobin Concentration Impacts Viscoelastic Hemostatic Assays in ICU Admitted Patients*

Abstract

OBJECTIVES: Low hemoglobin concentration impairs clinical hemostasis across several diseases. It is unclear whether hemoglobin impacts laboratory functional coagulation assessments. We evaluated the relationship of hemoglobin concentration on viscoelastic hemostatic assays in intracerebral hemorrhage (ICH) and perioperative patients admitted to an ICU. DESIGN: Observational cohort study and separate in vitro laboratory study. SETTING: Multicenter tertiary referral ICUs. PATIENTS: Two acute ICH cohorts receiving distinct testing modalities: rotational thromboelastometry (ROTEM) and thromboelastography (TEG), and a third surgical ICU cohort receiving ROTEM were evaluated to assess the generalizability of findings across disease processes and testing platforms. A separate in vitro ROTEM laboratory study was performed utilizing ICH patient blood samples. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Relationships between baseline hemoglobin and ROTEM/TEG results were separately assessed across patient cohorts using Spearman correlations and linear regression models. A separate in vitro study assessed ROTEM tracing changes after serial hemoglobin modifications from ICH patient blood samples. In both our ROTEM (n = 34) and TEG (n = 239) ICH cohorts, hemoglobin concentrations directly correlated with coagulation kinetics (ROTEM r: 0.46; p = 0.01; TEG r: 0.49; p < 0.0001) and inversely correlated with clot strength (ROTEM r: –0.52, p = 0.002; TEG r: –0.40, p < 0.0001). Similar relationships were identified in perioperative ICU admitted patients (n = 121). We continued to identify these relationships in linear regression models. When manipulating ICH patient blood samples to achieve lower hemoglobin concentrations in vitro, we similarly identified that lower hemoglobin concentrations resulted in progressively faster coagulation kinetics and greater clot strength on ROTEM tracings. CONCLUSIONS: Lower hemoglobin concentrations have a consistent, measurable impact on ROTEM/TEG testing in ICU admitted patients, which appear to be artifactual. It is possible that patients with low hemoglobin may appear to have normal viscoelastic parameters when, in fact, they have a mild hypocoagulable state. Further work is required to determine if these tests should be corrected for a patient’s hemoglobin concentration.

Hemoglobin Concentration and Viscoelastic Tests: Remember to Consider Fibrinogen and Platelets

“…Yet, analytical factors that link worsening anemia to increasing viscoelastic stability shed a dim light on the clinical interpretation and management of hemorrhage. Our results only partially fit the observations by Roh et al (1). In particular, it seems that the analytical paradox “lower hemoglobin-faster/stronger clot” at viscoelastic analysis may be verified only when the decline in hemoglobin is not followed by a reduction in fibrinogen and platelets, as observed before (3).…”

“…In particular, it seems that the analytical paradox “lower hemoglobin-faster/stronger clot” at viscoelastic analysis may be verified only when the decline in hemoglobin is not followed by a reduction in fibrinogen and platelets, as observed before (3). While this phenomenon may happen in bleedings that are clinically significant but without a significant loss of hemostatic components (such as intracranial hemorrhage), a word of caution must be spent when trying to translate the results by Roh et al (1) to other categories, such as trauma. In the latter setting, bleeding leads to a concomitant loss of hemoglobin, fibrinogen, and platelets, which is usually well represented by viscoelastic tests with longer clot formation times and reduced amplitude.…”

“…To the Editor: W e read with interest the article by Roh et al (1) published in the recent issue of Critical Care Medicine about hemoglobin concentration and viscoelastic tests. This brought us to reanalyze our previous work (2), where ICU patients receiving venovenous extracorporeal membrane oxygenation for acute respiratory distress syndrome and anticoagulated with heparin were randomized to receive or not antithrombin supplementation.…”

Viscoelastic Tests in the ICU Setting Helpful or Not?

“…We appreciate the study of Roh et al (1) highlighting the impact of hematocrit on coagulation, but we should keep in mind that anemic patients with the same plasma concentration like nonanemic patients have indeed higher clot firmness, which is not an artificial effect and is identified by FIBTEM.…”

The Effects of RBC Concentration on the Viscoelastic Assessment of Coagulation*

“…In particular, COVID-19 has provoked a large body of important work (13, 14) with viscoelastic assays playing a prominent role. Hence, a more nuanced interpretation of these tests is required, and the work of Roh et al (11) adds a helpful dimension to this conversation.…”