TEG and ROTEM Flashcards
What does TEG measure ?
- measures the elastic shear or storage modulus of clotting blood
- it is independent of sample viscosity
- viscosity can be affected by cryoglobulins, polycythemia etc
- uses whole blood
- pin in cup suspended by a wire
- width of the tracing is proportional to the magnitude of elastic shear
- higher the platelet count and fibrinogen
- the higher the maximum elastic shear
How many measurements are made on the TEG
and what are they?
- Five measurements
- R: reaction time
- K: coagulation time
- alpha: angle
- MA: maximum amplitude
- A60: amplitude at 60 minutes
In TEG, what does R signify?
- reaction time
- similar to whole blood clotting time
- measured at the start of the tracing where the curve is 1 mm wide
- Prolongation:
- clotting factor deficiencies or inhibitors
- anticoagulants like Heparin
- Thrombocytopenia
- platelets provide the phospholipid surface for coagulation reactions
In TEG, what does K signify?
- coagulation time
- distance or time from the 1 mm wide point to the 20 mm wide point
- The K value and alpha angle
- indicate the rate of increase in the shear modulas
In TEG, what does the alpha angle signify?
- angle is measured between the midline and drawn from the 1mm wide point tangential to the curve
Note: the K value and the alpha angle are very complex interpretations. Measure how fast the clot is forming.
What can cause abnormal K values and alpha angles in TEG?
- clotting factor deficiencies
- platelet dysfunction
- thrombocytopenia
- hypofibrinogenemia
In TEG, what does the max amplitude signify?
- the width of the curve at the widest point
- maximum clot elastic shear
- primarily a function of platelet count and fibrinogen level (structural components of the clot)
- both affect the MA, but perhaps platelets affect it a little bit more
What situations decrease the max amplitude ?
- thrombocytopenia
- hypofibrinogenemia
- severe factor deficiencies
- Heparin therapy
In TEG, what does A60 signify?
- Amplitude at 60 minutes
- IF lower than MA, signifies significant fibrinolysis
- Note: the longer you wait to measure the final A, the more likely you are to detect weak fibrinolytic activity
- In liver transplantation, severe fibrinolysis is common so evaluation every 15 minutes is frequently done
Why is the temperature of the pin and cup
so important in TEG evaluations ?
- all testing /measurements made at 37 degrees
- cold cups or pins will slow the clotting reaction
- falsely prolong the R value
What is the advantage of using citrated blood on
the TEG?
- can run the TEG in the core lab and also run other assays
- can check the sample for Heparin contamination using Thrombin times
- especially if the R and K values are long
- also low alpha angle
- Sample is stable for several hours so can treat with protamine sulfate to neutralize the Heparin
How does excess citrate affect the R time ?
- IF the tube is not filled appropriately there will be more anticoagulant compared to sample
- R value will be prolonged
Note: if unexpected long R values or straight lines, check for the presence of Heparin using thrombin time
How is ROTEM different from TEG?
- Both assess clot formation and dissolution kinetics and strength
- due this by measuring the rotational force
- In ROTEM
- the wire/ball rotates rather than the cup
- can analyze 4 samples at once
- TEG can only do 2 samples
What is the pitfall when using citrated whole blood for
evaluation by TEG ?
- known to produce profiles that are artifactually hypercoagulable relative to uncitrated samples
- also can produce similar profiles artifactually consistent with unfractionated Heparin reversal in some ECMO patients
