Learning Resources

Tools and materials to support your growth as a clinician

Welcome to our Learning Resources page — a growing collection of educational tools contributed by our faculty and fellows. Whether you're preparing for clinical practice or deepening your knowledge in a specific area, we hope you find these resources valuable!

ROTEM

Curated by Alastair Moody, MD

Rotational thromboelastometry (ROTEM) is a point-of-care viscoelastic test that provides real-time analysis of blood coagulation, clot formation, and fibrinolysis. Assays include EXTEM, INTEM, FIBTEM, HEPTEM, and APTEM. Each of these measure different parts of the coagulation process and help determine which product to transfuse. 

A ROTEM analysis produces a graphical tracing called a temogram for each of these assays. Within each assay there are parameters such as:

  • Clotting time (CT): Time from the start of the test until the clot reaches an amplitude of 2 mm. CT primarily reflects the initiation of coagulation and the availability of coagulation factors in the ability to generate thrombin 
  • Clot formation time (CFT) and alpha angle: Describe the speed of clot propagation: linking platelets together with fibrinogen 
  • A5 and A10: Clot amplitude 5 and 10 minutes after the clotting time. These provide early estimates of clot strength, which correlate to maximum clot firmness. An A10 + 10 will approximate your MCF. 
  • Maximum clot firmness (MCF): describes the greatest clot strength reached during the test. MCF reflects the combined contributions of platelets, fibrin polymerization, platelets, and factor XIII. Platelets contribute about 75% of the overall clot strength. Fibrinogen is converted into fibrin by thrombin. 
  • Maximum lysis (ML): demonstrates the percentage of breakdown in clot firmness relative to the maximum clot firmness 
ROTEM analysis flowchart

EXTEM

EXTEM is activated with tissue factor and evaluates the extrinsic coagulation pathway (Factor 7) as well as factors 2, 5, 10, and 13 in the common pathway.

FIBTEM

FIBTEM is activated with tissue factor (same as EXTEM) but it also contains a platelet inhibitor such as cytochalasin D. By suppressing platelet action, FIBTEM isolates the contribution of the fibrin-based clot strength

Comparing EXTEM clot firmness (A10, A20, MCF) with FIBTEM clot firmness allows for targeted intervention. For example:

  • Low EXTEM and low FIBTEM clot firmness (A10 <7mm): Suggests a relative fibrinogen deficiency 
  • Low EXTEM with relatively preserved FIBTEM: Suggests a relative platelet  deficiency 
  • It is important to remember that standard ROTEM assays do not reliably detect the effects of antiplatelet medications such as aspirin and Plavix

APTEM

APTEM is activated with tissue factor (same as EXTEM) but contains an antifibrinolytic agent such as aprotinin. This should correct hyperfibrinolysis if seen on the EXTEM temogram

INTEM

INTEM uses ellagic acid as a contact activator and evaluates coagulation through activation of the intrinsic pathway. It evaluates intrinsic pathway factors 8, 9, 11, 12 as well as factors 2, 5, 10, and 13 in the common pathway. It is used to monitor deficiencies affecting intrinsic-pathway coagulation factors and to the effects of unfractionated heparin.

HEPTEM

HEPTEM is activated ellagic acid as a contact activator (same as INTEM) but contains heparinase, which neutralizes heparin in the sample. Its primary role is to determine whether unfractionated heparin is responsible for a prolonged INTEM CT.

For example:

  • Prolonged INTEM CT with a normal or shorter HEPTEM CT: Supports a clinically relevant heparin effect.
  • Both INTEM and HEPTEM CT prolonged: Suggests that the abnormality is not fully explained by heparin and may reflect coagulation-factor deficiency

HEPTEM is frequently utilized and after cardiopulmonary bypass, after protamine administration, and in other settings in which residual heparin is suspected