How Viscoelastic Testing is Revolutionizing Blood Management
A comprehensive look at the technology transforming haemostasis diagnosis and management
Imagine a world where doctors can watch your blood form clots in real time, like engineers monitoring the structural integrity of a building during an earthquake.
This isn't science fiction—it's the power of viscoelastic testing (VET), a revolutionary approach to understanding blood clotting that's transforming how we manage bleeding disorders. Every year, millions of people worldwide experience serious bleeding during surgery, after trauma, or during childbirth. How clinicians respond to that bleeding can mean the difference between life and death.
Traditional blood tests provide limited information, like knowing the ingredients of a cake but not watching it bake. VET changes all that by allowing us to observe the entire clotting process from start to finish 1 .
Haemostasis—our body's ability to stop bleeding—represents a delicate balance between clotting and bleeding. When this balance is disrupted, the consequences can be severe. For decades, doctors relied on standard laboratory tests like prothrombin time (PT) and activated partial thromboplastin time (aPTT) to assess clotting function.
Viscoelastic testing has evolved dramatically since its initial conception in 1948, transforming from a cumbersome manual technique to an automated, sophisticated point-of-care technology.
At its core, viscoelastic testing measures the physical properties of a blood clot as it forms and then breaks down. The term "viscoelastic" combines viscosity (resistance to flow) and elasticity (ability to return to original shape after deformation)—two key properties of blood clots. Unlike traditional tests that are performed on plasma (the liquid component of blood), VET uses whole blood, preserving the crucial interactions between plasma proteins, platelets, and other blood cells that occur in the body 1 .
The most common VET systems are Thromboelastography (TEG®) and Rotational Thromboelastometry (ROTEM®). While they differ in some technical aspects, both operate on similar principles:
The result is a characteristic curve that tells a story about the clotting process, with each parameter revealing a different chapter of that story 1 4 .
| Parameter | What It Measures | Clinical Significance |
|---|---|---|
| Clotting Time (R/CT) | Time until first clot formation | Coagulation factor deficiency if prolonged |
| Clot Formation Time (K/CFT) | Speed of clot formation | Fibrinogen deficiency if prolonged |
| Alpha Angle (α) | Rate of clot strengthening | Platelet function and fibrinogen activity |
| Maximum Amplitude (MA/MCF) | Maximum clot strength | Platelet count and function, fibrinogen |
| Lysis Parameters (LY30, CLT) | Clot breakdown | Fibrinolysis (excessive if elevated) |
These parameters provide clinicians with a comprehensive picture of haemostasis that no single conventional test can match. Within minutes, they can identify whether bleeding is due to platelet problems, clotting factor deficiencies, fibrinogen issues, or excessive clot breakdown—information that is crucial for targeting treatment appropriately 5 .
Cardiac surgery represents one of the most well-established applications for VET. Patients undergoing heart surgery with cardiopulmonary bypass are particularly vulnerable to bleeding complications because the bypass process alters clotting function significantly .
A comprehensive analysis of randomized trials showed that VET-guided transfusion strategies in cardiac surgery patients led to significant reductions in:
Perhaps most importantly, this targeted approach didn't increase mortality, suggesting that giving fewer transfusions based on better information is both safe and effective 6 .
In severe trauma, bleeding is the leading cause of preventable death. The condition known as trauma-induced coagulopathy affects up to 25% of seriously injured patients and dramatically increases mortality 5 .
VET shines in this environment because it can provide actionable results within 10-15 minutes. Studies have shown that VET parameters are better predictors of massive transfusion needs and mortality following trauma than conventional tests 7 .
of seriously injured trauma patients develop trauma-induced coagulopathy
While much of the focus with VET has been on bleeding, these tests also provide insights into thrombosis risk. This is particularly valuable in patients with liver disease, who often walk a tightrope between bleeding and clotting risks.
Despite having abnormal conventional coagulation tests, most patients with chronic liver disease have "rebalanced" haemostasis—they can still form clots effectively and are actually at increased risk for thrombotic complications 8 .
VET parameters have shown promise in predicting which liver disease patients are at highest risk for thrombosis, potentially guiding decisions about anticoagulant therapy 8 .
To understand how VET performs in real-world settings, let's examine a pivotal study that compared VET-guided transfusion with conventional practice in cardiac surgery patients. This randomized controlled trial—among the largest of its kind—enrolled over 1,900 patients undergoing cardiac surgery with cardiopulmonary bypass at multiple medical centers .
Patients were randomly assigned to one of two groups:
The research team used a standardized approach across all centers to ensure consistency. When bleeding occurred, clinicians in the VET group followed specific algorithms that matched transfusion recommendations to abnormal parameters .
The results offered compelling evidence for VET implementation. While there was no significant difference in the overall proportion of patients receiving any blood product or in mortality rates, the VET-guided approach led to important reductions in specific blood product transfusions 6 .
| Outcome Measure | VET-Guided Group | Control Group | Relative Risk Reduction |
|---|---|---|---|
| RBC transfusion | 45.2% | 49.6% | 9% |
| Platelet transfusion | 27.1% | 40.9% | 34% |
| Plasma transfusion | 19.3% | 33.3% | 42% |
| Cryoprecipitate use | 12.9% | 18.5% | 30% |
| Mortality | 2.5% | 3.1% | Not significant |
These findings suggest that VET guidance doesn't necessarily mean fewer patients will need transfusions overall, but rather that those who do need them receive more appropriate, targeted products in the right amounts. This precision approach aligns with the modern medical ethos of personalized care while simultaneously reducing strain on often-limited blood bank resources 6 .
Perhaps surprisingly given the reduction in transfusions, patients in the VET group did not experience higher rates of bleeding complications or need for reoperation. This supports the safety of a more conservative, evidence-based transfusion approach guided by VET .
Behind every VET test is a sophisticated array of reagents and activators that allow clinicians to probe specific aspects of the clotting cascade. These reagents are the "tools" that transform the basic technology into a targeted diagnostic system 1 .
| Reagent/Activator | Function | Clinical Application |
|---|---|---|
| Kaolin | Contact activator | General assessment of clotting pathway |
| Tissue factor | Strong activator of extrinsic pathway | Rapid assessment of coagulation |
| Cytochalasin D | Platelet inhibitor | Isolates fibrinogen contribution to clot |
| Heparinase | Heparin neutralizer | Assess coagulation in heparinized patients |
| Aprotinin | Fibrinolysis inhibitor | Differentiate hyperfibrinolysis |
| Russell's viper venom | Factor X activator | Detect direct oral anticoagulants |
Modern VET systems like the TEG 6s® and ClotPro® have incorporated these reagents into multi-channel cartridges that can run several tests simultaneously on the same blood sample. This parallel testing capability dramatically reduces the time to comprehensive results—a critical advantage in bleeding emergencies 1 .
The evolution of specialized reagents has also expanded VET into new applications, particularly in monitoring anticoagulant therapy. Tests specifically designed to detect and quantify the effects of direct oral anticoagulants (DOACs) like rivaroxaban and apixaban represent a significant advance over traditional coagulation tests, which were not designed for these newer medications 1 .
Beyond the clinical benefits, VET offers compelling economic advantages. The 2015 Health Technology Assessment review conducted a thorough cost-effectiveness analysis comparing VET with standard laboratory testing in both cardiac surgery and trauma patients 6 .
Cost savings per patient
Reduction in transfusion complications
Cost savings per patient
Reduction in resource utilization
These savings primarily resulted from reduced blood product usage, with additional benefits from decreased complications associated with transfusion. The analysis concluded that VET was not only clinically effective but also cost-saving—a rare combination in healthcare technology assessment 6 .
It's worth noting that these calculations considered not only the direct costs of the tests and blood products but also downstream costs associated with transfusion complications and extended hospital stays. The greater savings in trauma patients reflect the higher resource utilization typically required in managing severe trauma 6 .
As DOAC use expands, the need for reliable monitoring grows, particularly in scenarios like emergency surgery or bleeding events. Research shows strong correlations between VET parameters and DOAC plasma concentrations, suggesting a role in quickly assessing anticoagulant effect 1 .
Just as VET can guide bleeding management, it may also help tailor anticoagulant dosing for patients on heparin or other medications, potentially improving both safety and efficacy 8 .
The ability to assess overall coagulation status makes VET valuable in disseminated intravascular coagulation (DIC), a complex condition where patients may simultaneously experience bleeding and clotting. Studies show VET parameters correlate with DIC severity and may guide treatment 7 .
Children have developmental differences in their coagulation systems that make haemostasis management particularly challenging. Early research suggests VET may offer advantages over conventional tests in guiding paediatric transfusion 1 .
Emerging evidence suggests connections between coagulation parameters and immune response, potentially opening new applications for VET in monitoring patients with infections or inflammatory conditions 7 .
Viscoelastic point-of-care testing represents a paradigm shift in how we assess and manage bleeding disorders.
By providing a comprehensive, real-time view of the entire clotting process, VET moves us from reactive, recipe-based transfusion to proactive, targeted haemostasis management. The technology has proven particularly valuable in cardiac surgery and trauma, where rapid decisions based on complete information can dramatically alter outcomes.
While challenges remain—including standardization between different devices and establishing consensus thresholds for intervention—the evidence base supporting VET continues to grow. From its modest beginnings decades ago, viscoelastic testing has evolved into a sophisticated technology that simultaneously improves patient care and reduces healthcare costs.
As we look to the future, the expanding applications of VET promise to further personalize medicine, helping clinicians navigate the delicate balance between bleeding and clotting across diverse patient populations and clinical scenarios. The journey of a single blood sample from vial to value exemplifies how technology continues to transform medicine, one clot at a time.