Thromboelastography, often shortened to TEG, is a blood clotting test that shows how a clot forms, how strong it becomes, and whether it breaks down too quickly. Instead of looking at one isolated part of clotting, TEG follows the clotting process in whole blood from the first fibrin strands to the final clot strength. This makes it useful during major bleeding, trauma, surgery, liver transplant care, postpartum hemorrhage, and other situations where doctors need fast decisions about plasma, platelets, fibrinogen, or antifibrinolytic medicine. TEG does not replace every clotting test. It works best when interpreted with the patient’s condition, medication history, platelet count, fibrinogen level, PT/INR, aPTT, and signs of bleeding or clotting. A normal result is reassuring in many urgent settings, but abnormal results need careful interpretation because ranges differ by analyzer, reagent, hospital protocol, and patient group.
- TEG measures clot speed, clot strength, and clot breakdown using whole blood rather than plasma alone.
- Typical kaolin TEG ranges include R time about 5–10 minutes, K time about 1–3 minutes, alpha angle about 53–72 degrees, MA about 50–70 mm, and LY30 usually below 8%, but local lab ranges matter most.
- A prolonged R time usually points to delayed clot initiation from clotting factor deficiency, heparin effect, anticoagulant effect, severe dilution, or liver-related coagulopathy.
- A low maximum amplitude usually points to a weak clot from low platelets, platelet dysfunction, low fibrinogen, or combined clot-strength problems.
- A high LY30 suggests excess clot breakdown, called hyperfibrinolysis, which becomes urgent when active bleeding is present.
- TEG usually requires no fasting, but blood thinners, antiplatelet medicines, transfusions, pregnancy, liver disease, trauma, and inflammation all affect interpretation.
Table of Contents
- What Is a TEG Test?
- How TEG Works During Clot Formation
- TEG Results, Parameters, and Typical Ranges
- What Abnormal TEG Results Usually Mean
- When Doctors Use TEG
- TEG vs Standard Clotting Tests
- Preparation, Sample Issues, and Limitations
- What Happens After an Abnormal TEG Result?
What Is a TEG Test?
A TEG test is a functional clotting test that measures how well blood forms a stable clot. The test uses whole blood, so it reflects the interaction between clotting proteins, fibrinogen, platelets, red blood cells, and clot breakdown. This is different from many routine clotting tests, which use plasma and focus on selected parts of the coagulation pathway.
TEG belongs to a group of tests called viscoelastic hemostatic assays. “Viscoelastic” means the test measures how the blood sample changes from a liquid into a thicker, more elastic clot. As the clot forms, the machine records the changing strength of the clot over time and creates a tracing.
The main value of TEG is speed and pattern recognition. In active bleeding, a clinician needs to know whether the main issue is delayed clot start, poor fibrinogen support, weak platelet-driven clot strength, or excessive clot breakdown. TEG helps answer those questions in minutes, not hours.
TEG is most useful in hospitals, operating rooms, emergency departments, intensive care units, trauma bays, and transplant centers. It is not usually ordered as a general screening test during a routine physical. A standard coagulation panel remains more common for broad clotting evaluation, especially when the clinical situation is not urgent.
TEG also helps avoid “one-size-fits-all” transfusion decisions. Two patients with bleeding can have very different clotting problems. One needs fibrinogen support. Another needs platelets. Another needs anticoagulant reversal. Another needs treatment for excess fibrinolysis. TEG gives a clotting pattern that supports more targeted care.
The test does not diagnose one disease by itself. It does not prove why someone is bleeding or clotting. It shows the current behavior of the blood sample under test conditions. The result becomes meaningful when matched with the patient’s symptoms, recent surgery or injury, medication list, liver function, blood count, and other clotting tests.
How TEG Works During Clot Formation
TEG follows a blood sample as it clots inside a specialized device. In classic TEG, blood is placed in a small cup with a pin suspended in the sample. As the clot forms between the cup and the pin, the clot transmits more movement. The instrument converts those mechanical changes into a curve.
Newer TEG systems use cartridge-based technology and resonance-based measurement rather than the classic cup-and-pin setup. The goal is the same: measure the clot’s changing physical strength from start to breakdown.
The test is often performed on citrated whole blood. Citrate prevents the sample from clotting before testing by binding calcium. The analyzer then adds calcium back and uses an activator, such as kaolin or tissue factor, depending on the assay. Different activators produce different timing and different reference ranges.
Clotting is measured as a process, not a single moment
Routine clotting tests often stop at the first fibrin formation. TEG continues further. It tracks several phases:
- Clot initiation: how long it takes for the first measurable clot to form.
- Clot propagation: how quickly the clot builds strength.
- Clot strengthening: how firm the clot becomes at its strongest point.
- Clot breakdown: how much the clot dissolves after reaching peak strength.
This whole-process view is the reason TEG is useful in major bleeding. A patient can have a normal early clotting time but poor clot strength. Another patient can form a clot normally but break it down too fast. TEG shows these different patterns more directly than PT, INR, or aPTT alone.
Standard TEG, rapid TEG, and platelet mapping are not identical
Standard kaolin TEG commonly measures clot initiation, clot build-up, maximum clot strength, and lysis. Rapid TEG uses stronger activation, often tissue factor, to produce faster results during trauma or urgent bleeding care. Some hospitals use rapid TEG because early information helps guide massive transfusion decisions.
TEG platelet mapping is a separate use of the technology. It estimates platelet inhibition related to drugs such as aspirin or P2Y12 inhibitors, including clopidogrel. It is not the same as a standard TEG result. A person can have a standard TEG that looks acceptable while still having clinically important platelet inhibition from antiplatelet medication. When medication-related platelet dysfunction is the main question, doctors often use a platelet-focused test or a dedicated platelet function test.
TEG Results, Parameters, and Typical Ranges
TEG reports several values. Each value describes a different part of clot formation or breakdown. The names and ranges vary by platform, reagent, and local protocol, so the reference interval printed on the lab report is the best range for that specific result.
The most common parameters are R time, K time, alpha angle, maximum amplitude, and LY30. Some reports also include a coagulation index, G value, or functional fibrinogen result.
| TEG parameter | What it measures | Typical kaolin TEG range | Main clinical clue |
|---|---|---|---|
| R time | Time until initial clot formation | About 5–10 minutes | Clotting factor activity, heparin or anticoagulant effect |
| K time | Time for the clot to reach a set level of firmness | About 1–3 minutes | Speed of clot build-up, fibrinogen and platelet contribution |
| Alpha angle | Rate of clot strengthening | About 53–72 degrees | Fibrin build-up and clot propagation |
| Maximum amplitude (MA) | Strongest clot firmness | About 50–70 mm | Platelet-fibrin clot strength |
| LY30 | Percent clot breakdown 30 minutes after MA | Often 0–8%, with lower upper limits in some labs | Fibrinolysis, or clot breakdown |
| Coagulation index (CI) | Combined score from several TEG values | Often -3 to +3 | Overall hypo- or hypercoagulable pattern |
A “normal TEG” means the blood sample formed a clot within the expected timing and strength range for that assay. In urgent bleeding care, a normal TEG often suggests that severe global clotting failure is not the main cause of bleeding. The source of bleeding may be surgical, anatomic, vascular, or related to a local injury instead.
A “low clot strength” result does not automatically mean the platelet count is low. Platelets can be present in normal numbers but work poorly because of aspirin, clopidogrel, uremia, shock, hypothermia, trauma, or severe illness. For that reason, doctors interpret MA alongside the platelet count, fibrinogen concentration, medication history, and the clinical picture.
A fibrinogen-focused TEG assay, often called functional fibrinogen or a similar platform-specific name, helps separate fibrinogen contribution from platelet contribution. This matters because standard MA reflects both platelets and fibrin. When clot strength is low, the question is not only “Is the clot weak?” but “Which part of the clot is weak?”
What Abnormal TEG Results Usually Mean
Abnormal TEG results are best read as patterns. One number rarely tells the whole story. The same patient can have delayed clot initiation, slow clot build-up, low maximum strength, and excess lysis at the same time, especially during massive bleeding, liver failure, trauma, or severe dilution from fluids and transfusion.
Prolonged R time: clot formation starts too slowly
A high or prolonged R time means the blood sample took too long to start clotting. This often points to reduced clotting factor activity or an anticoagulant effect.
Common causes include:
- Unfractionated heparin effect
- Warfarin effect, though TEG does not reliably replace INR for warfarin monitoring
- Severe clotting factor deficiency
- Major blood loss with factor depletion
- Dilution from large-volume fluids or transfusion
- Severe liver disease
- Disseminated intravascular coagulation in a bleeding phase
- Direct oral anticoagulants in some settings, depending on drug level and assay sensitivity
A prolonged R time during active bleeding often pushes the care team to consider plasma, prothrombin complex concentrate, heparin reversal, or other targeted reversal strategies. The exact treatment depends on the cause, the medication involved, bleeding severity, and local protocol.
A short R time means clotting starts faster than expected. This is often described as a hypercoagulable pattern, especially when paired with high clot strength. It does not prove that a person has a blood clot, but it raises concern when the patient also has risk factors or symptoms.
Prolonged K time or low alpha angle: clot strength builds too slowly
A prolonged K time or low alpha angle means the clot forms but builds strength slowly. This pattern often points to low fibrinogen, poor fibrin polymerization, low platelets, platelet dysfunction, or a combined problem.
Fibrinogen is one of the first clotting factors to fall during major bleeding. It is also important in trauma, postpartum hemorrhage, liver disease, and disseminated intravascular coagulation. A separate fibrinogen blood test helps confirm whether the fibrinogen level is low enough to need replacement.
A low alpha angle with low functional fibrinogen strength often directs treatment toward cryoprecipitate or fibrinogen concentrate when bleeding is present. A low alpha angle with low platelet contribution points toward platelet-related support instead.
Low MA: the clot is too weak
A low maximum amplitude means the strongest clot was weaker than expected. MA depends heavily on platelets, but fibrin also contributes. A low MA is one of the most practical TEG findings because it directly addresses clot strength.
Common causes include:
- Low platelet count
- Platelet dysfunction
- Aspirin, clopidogrel, ticagrelor, or other antiplatelet effect
- Uremia from kidney failure
- Low fibrinogen
- Severe trauma-related platelet dysfunction
- Hypothermia or acidosis in major bleeding
- Liver disease
- Massive transfusion or dilutional coagulopathy
During active bleeding, a low MA often leads clinicians to consider platelets, desmopressin in selected platelet dysfunction situations, fibrinogen replacement, or correction of hypothermia and acidosis. Treatment decisions must match the cause. Giving platelets for every low MA is too simple because fibrinogen can be the bigger problem in some patients.
High MA or high CI: the clot is unusually strong
A high MA means the clot reached stronger-than-expected firmness. This can occur with high platelet activity, high fibrinogen, inflammation, cancer, trauma recovery, pregnancy, postoperative states, and some critical illnesses.
A high MA does not diagnose deep vein thrombosis, pulmonary embolism, stroke, or heart attack. It means the tested blood sample has a stronger clotting tendency under the assay conditions. If a patient has leg swelling, chest pain, shortness of breath, neurologic symptoms, or other concerning symptoms, imaging and diagnosis-specific testing matter more than TEG alone. For suspected clot breakdown or clot-related evaluation, a D-dimer blood test has a different role and is interpreted in a different clinical pathway.
High LY30: the clot breaks down too quickly
LY30 measures how much clot strength is lost 30 minutes after the clot reaches its maximum amplitude. A high LY30 suggests hyperfibrinolysis, meaning the body is breaking down clots too aggressively.
Hyperfibrinolysis is a serious finding during trauma, major surgery, postpartum hemorrhage, liver transplant care, and massive bleeding. In the right setting, it supports use of antifibrinolytic medicine such as tranexamic acid or aminocaproic acid. Timing matters. Antifibrinolytic treatment is most useful when matched to the patient’s condition, bleeding pattern, and institutional protocol.
A low LY30 is not always “better.” Some critically ill or trauma patients show fibrinolysis shutdown, where clot breakdown is suppressed. This pattern has been linked with thrombotic risk in some studies, but it is not a stand-alone reason to start or stop anticoagulation without a broader clinical decision.
When Doctors Use TEG
TEG is most valuable when clotting status is changing quickly and treatment decisions are time-sensitive. It is not usually ordered for mild bruising alone or as a general wellness test.
Common uses include:
- Severe trauma with bleeding or risk of massive transfusion
- Major surgery with active bleeding
- Cardiac surgery, especially after cardiopulmonary bypass
- Liver transplant surgery and advanced liver disease care
- Postpartum hemorrhage
- Intensive care patients with complex bleeding or clotting concerns
- Monitoring heparin effect or heparin reversal in selected settings
- Evaluating unexplained bleeding when routine tests do not explain the problem
- Guiding targeted blood product use during massive hemorrhage protocols
In trauma, TEG helps identify whether the patient needs plasma, platelets, fibrinogen support, or treatment for excess fibrinolysis. Standard tests such as PT, INR, and aPTT often take longer and do not show clot strength or lysis in the same real-time way.
In cardiac surgery, TEG helps separate residual heparin effect, platelet dysfunction, fibrinogen depletion, and surgical bleeding. A patient can bleed after bypass because the surgical site is not fully controlled, because platelets are impaired, because fibrinogen is low, or because heparin reversal is incomplete. TEG helps the team avoid guessing.
In liver disease and liver transplant care, TEG is useful because routine tests can look very abnormal without matching the true bleeding risk. INR is often elevated in advanced liver disease, but the clotting system is “rebalanced” in complex ways. TEG gives a functional snapshot, though it still does not capture everything that happens inside blood vessels.
In postpartum hemorrhage, fibrinogen can fall early and bleeding can worsen quickly. TEG or related viscoelastic testing helps identify low fibrin-based clot strength and supports timely fibrinogen-focused therapy when the clinical picture fits.
TEG is less useful as a broad outpatient test for “clot risk” in a person with no symptoms. It is also not the main test for inherited thrombophilia, antiphospholipid syndrome, hemophilia, von Willebrand disease, or monitoring most long-term anticoagulant therapy. Those situations need specific tests chosen for the suspected condition.
TEG vs Standard Clotting Tests
TEG and standard clotting tests answer different questions. The best evaluation often uses both.
PT and INR measure the extrinsic and common clotting pathways in plasma. They are essential for warfarin monitoring and for many liver-related and factor-related questions. A prothrombin time test or INR result does not measure platelet-driven clot strength or clot breakdown.
aPTT measures the intrinsic and common clotting pathways in plasma. It is useful for heparin monitoring in some settings, factor deficiencies, lupus anticoagulant workups, and unexplained prolonged clotting time. An aPTT result does not show the strength of the final clot.
Fibrinogen testing measures the concentration or activity of fibrinogen, depending on method. Platelet count measures platelet number. Thrombin time, anti-Xa, D-dimer, and factor activity tests answer still different questions. TEG brings several clotting functions into one dynamic tracing, but it does not replace these tests.
| Test | Main sample type | What it shows well | What it misses or shows poorly |
|---|---|---|---|
| TEG | Whole blood | Clot initiation, clot build-up, clot strength, lysis | Specific factor diagnosis, exact drug levels, vessel-wall biology |
| PT/INR | Plasma | Warfarin effect, extrinsic pathway delay, liver-related synthetic changes | Platelet function, clot strength, fibrinolysis |
| aPTT | Plasma | Intrinsic pathway delay, some heparin effects, selected factor deficiencies | Final clot strength, platelet contribution, fibrinolysis |
| Platelet count | Whole blood | Number of platelets | How well platelets function |
| Fibrinogen | Plasma | Fibrinogen level or activity | Whole-clot strength and platelet interaction |
| D-dimer | Plasma | Evidence of fibrin formation and breakdown | Real-time clot strength or transfusion guidance |
The practical difference is this: standard clotting tests identify specific pathway abnormalities, while TEG shows how the clot behaves as a whole. In major bleeding, that whole-clot view is valuable. In diagnosis of a specific inherited or medication-related disorder, targeted lab tests remain necessary.
For heparin treatment, TEG sometimes contributes useful information, especially with heparinase comparison assays. Still, anti-Xa testing remains a common direct way to evaluate heparin level in many hospital protocols. An anti-Xa test answers a different question than TEG: how much heparin-like anticoagulant activity is present.
Preparation, Sample Issues, and Limitations
Most people do not need to fast before a TEG test. In hospital settings, the test is often ordered urgently, so preparation is minimal. The most important preparation is accurate medication and clinical history.
Tell the care team about:
- Warfarin, heparin, enoxaparin, apixaban, rivaroxaban, dabigatran, or edoxaban
- Aspirin, clopidogrel, prasugrel, ticagrelor, or other antiplatelet drugs
- Recent transfusions or clotting factor treatments
- Tranexamic acid or aminocaproic acid
- Liver disease, kidney failure, pregnancy, cancer, infection, or recent major trauma
- Known bleeding disorders or prior abnormal clotting tests
- Recent surgery, childbirth, or major procedures
TEG is sensitive to sample handling. A clotted sample, wrong tube fill, delayed testing, poor mixing, temperature differences, or incorrect reagent handling can distort results. Citrated samples usually need testing within a defined time window, often within a couple of hours. Native whole-blood testing requires immediate analysis.
Reference ranges are another limitation. There is no single universal normal range for all TEG testing. A result from a classic kaolin TEG, rapid TEG, TEG 6s cartridge, heparinase channel, or functional fibrinogen channel should not be interpreted with the wrong reference interval. Pediatric patients, pregnant patients, older adults, trauma patients, and liver disease patients also have different baseline clotting patterns.
TEG also has biological limits. It tests blood in a device, not inside a living blood vessel. Real bleeding and clotting depend on blood flow, vessel injury, endothelial function, blood pressure, calcium level, pH, body temperature, tissue injury, and surgical control of bleeding. A patient can bleed heavily from an injured artery even when TEG is normal.
A normal TEG does not rule out every bleeding disorder. Von Willebrand disease, mild platelet function disorders, medication effects, factor XIII deficiency, and certain vascular or connective tissue disorders require specific evaluation. A high TEG clot-strength pattern does not prove a person has a dangerous clot. Imaging and diagnosis-specific testing are still needed when symptoms suggest deep vein thrombosis, pulmonary embolism, stroke, or heart attack.
The safest interpretation is pattern-based and context-based. TEG is powerful when it guides urgent hemostatic treatment, but it should not be used in isolation to make broad conclusions about lifelong bleeding or clotting risk.
What Happens After an Abnormal TEG Result?
The next step depends on the abnormal pattern and whether the patient is actively bleeding, about to undergo a procedure, recovering from surgery, or being evaluated for clotting risk.
During active bleeding, clinicians act quickly. A prolonged R time often leads to evaluation for clotting factor replacement or anticoagulant reversal. A low alpha angle or fibrinogen-related weakness often leads to fibrinogen-focused treatment. A low MA often leads to platelet-focused evaluation or therapy. A high LY30 supports treatment for excess fibrinolysis when the clinical situation fits.
When there is no active bleeding, an abnormal TEG is usually not treated automatically. Doctors repeat the test, check for sample problems, review medications, compare with PT/INR, aPTT, fibrinogen, platelet count, and liver or kidney tests, and decide whether the result matches the person’s symptoms.
A helpful way to understand follow-up is to match the TEG pattern with the clinical question:
| TEG pattern | Common follow-up focus | Possible related tests |
|---|---|---|
| Prolonged R time | Factor deficiency, heparin effect, anticoagulant effect, liver-related coagulopathy | PT/INR, aPTT, anti-Xa, medication review, factor tests |
| Prolonged K or low alpha angle | Low fibrinogen or slow fibrin clot build-up | Fibrinogen level, platelet count, repeat TEG functional fibrinogen channel |
| Low MA | Weak platelet-fibrin clot strength | Platelet count, platelet function testing, fibrinogen, medication review |
| High MA or high CI | Hypercoagulable pattern, inflammation, high fibrinogen, platelet activation | CBC, fibrinogen, inflammatory markers, imaging if symptoms suggest clot |
| High LY30 | Excess fibrinolysis | Repeat TEG, fibrinogen, D-dimer, clinical bleeding assessment |
Seek urgent medical care right away if abnormal clotting results occur with heavy bleeding, vomiting blood, black stools, severe headache, weakness on one side, new confusion, chest pain, shortness of breath, coughing blood, fainting, severe abdominal pain, or sudden leg swelling. Lab results matter, but symptoms drive urgency.
For non-urgent abnormal results, the best next step is a focused discussion with the ordering clinician. Ask which TEG parameter was abnormal, whether the result matched the clinical problem, whether the sample was reliable, which other tests support the finding, and whether the result changes treatment.
TEG is most useful when it answers a practical question: What part of clotting is failing right now, and what treatment addresses that failure? When used that way, it helps clinicians move from broad transfusion to targeted clotting support.
References
- Thromboelastography 2023 (Review)
- Review of Thromboelastography (TEG): Medical and Surgical Applications 2023 (Review)
- The European guideline on management of major bleeding and coagulopathy following trauma: sixth edition 2023 (Guideline)
- Management of severe peri-operative bleeding: Guidelines from the European Society of Anaesthesiology and Intensive Care: Second update 2022 2023 (Guideline)
- Viscoelastic haemostatic assays to guide therapy in elective surgery: an updated systematic review and meta-analysis 2025 (Systematic Review)
- Viscoelastic Hemostatic Assays in the Management of Trauma-Induced Coagulopathy: A Clinical Update 2026 (Review)
Disclaimer
This article is educational and does not replace care from a qualified medical professional. TEG results must be interpreted with symptoms, medications, bleeding severity, other clotting tests, and the lab’s own reference ranges. Seek urgent medical care for heavy bleeding, symptoms of a blood clot, stroke-like symptoms, chest pain, or shortness of breath.
