Hi Thomas,

Very interesting question.  APTT and PT tests are conventionally  used TO MONITOR the anticoagulant activity of heparin and warfarin respectively.  Although thrombin generation tests are good to early diagnose abnormal coagulation but how good they are to monitor heparin and warfarin perhaps need rigorous evaluation.  It seems that APTT and PT tests will continue to be used as long as heparin and warfarin continue to be used,.  Best Wishes,

Omer

Hi Omer,

as you write, thrombin generation triggered only by recalcification of plasma (RECA) is a very good ultra-specific thrombin generation test for prothrombotic alterations of the plasma matrix. For monitorization of the anticoagulant efficiency of any drug, thrombin generation has to be triggered much more strongly than in the RECA: TF should be added in an ultra-specific thrombin generation test called EXCA or ellagic acid should be added in an ultra-specific thrombin generation test called INCA.

Nice to hear from you ! Greetings to Chicago !

Thomas

Hi Thomas,

Good to hear from you.  The important point is that the thrombin generation tests have to be standardized to monitor the anticoagulant drugs.  You have to determine a therapeutic level for heparin, a therapeutic level for LMWH and not to mention the NOADs.  Until such time we have to do PT and APTT.

Best Wishes,

Omer

Hi Thomas,

please find in the attachment my published manuscripts. I hope you will find some valuable information.

Best wishes

Dragica

I think that the answer to this question is the conrtext in which the tests are to be used. If you are just doing a preop screen then a PT and APTT would surely suffice. If you are looking at more complicated issues such as inhibitor investigations then thrombin generation testing may provide far more information particularly bleeding tendency etc.

Hi Thomas

Most of the relevant things have been said. One point that one could expand on is the context in which you want to use these tests.

You mention "within the first golden hours of the disease". So if you're looking at complex coiagulation disorders including DIC, hemophilia with inhibitors or hypercoagulability, then thrombion genertaion is probably the way with the most promising future.

If you are looking at preoperative screening (with aPTT and/or PT), then I do not see much evidence in favor of such a strategy.  The two tests certainly are not predictive of perioperative bleeding. This strategy has been propagated for decades but in my view does not withstand a critical look. There is not only an absence of evidence in favor, there is even evidence strongly questioning such a practice. In today's setting of limited means in the health care system, an approach which identifies people at risk (f.e. by a valdiated questionnaire) and only investigates those at increased risk of bleeding should be further investigated. The Austrian anesthesiologists (OEGARI) are speerheading this approach.

If you want to monitor anticoagulants, I agree with Omer, that you have to use valdiated tests. If however you have done your homework and validated such tests at your institution, then go for it - use thrombin generation. The group of Claude Negrier has published quite a bit of interesting data on thrombin generation...

Finally, in my view the most interesting aspect of your question I would like to second. YES, we do need new tests or at least should revisit the tests that we use for fibrinogen measurement. That the "Clauss method" is standardised, I believe is a myth.  There is a lot to do in this field, certainly since the advent of strategies that advocate coagulation management with fibrinogen concentrates.

Kind regards

Lars

PS I still "owe" you a document, that you once requested. It is a compilation of works - that's why I hesitated ins ending in - with a short commentary. I will scan it and send it. Sorry for the delay

Yes, the thrombin generation tests have to be standardized. You should use polystyrene plates of highest quality (e.g. Brand plates), the plasma has to be fresh (less than 2h old, stored 23°C), the activator should be TF (EXCA) or ellagic acid (INCA), the 100% of normal value should be 0.5 IU/ml thrombin. Under These standard conditions any plasmatic anticoagulant can be measured by EXCA or INCA, you do not need an extra test for each anticoagulant. So, a clinically interesting value of 20% thrombin generation (= 0.1 IU/ml) reflects strong prophylactic/slight therapeutic anticoagulation.

Yes, the good old aPTT and especially PTT are sensitive to all variations in the Prot. C related pathway (in essence variations of Prot. C, Prot S and FV). Hence, the good old aPTT that served as a valuable screening tool for modifications in the intrinsic coagulation pathway could also serve as a Screening tool for Prot C & Prot  S deficiencies as well as FV Leiden. In other words: good old aPTT values within the normal range makes a defect in the Prot. C pathway highly unlikely and thus can Substitute for the aPC resistence assay. In contrast, the new and highly  specific aPTTs and the Ultra specific thrombin generation test cannot serve These screening purposes.

I don't understand your question. Exactly what are you trying to determine? 

Wellcome to the new test, if they become well standarized, but we can,t still supress the old APTT and TP, in spite their well recognized limitations.

Dear Thomas,

The TGT assays with low TF: are they really reflect more physiological clotting ? We use now also the TGT from the thrombodynamics analyser using 90 pM/m2 TF: assumed to reflect cell density of TF. Is that not relevant ?

To make it more complex: the TGT with 0,5 pM TF (TGA Technoclone) uses primarily the Josso loop and TGT is defective in factor IX and VIII deficiency (CTI sampling); while CAT 5 pM TGT is normal in these deficiencies. What is here the physiology issue ? In the Genesia they use 1 pM TF.

I am interested in your comments and discussion.

Kees

Dear Cornelis,

To study extrinsic thrombin generation you should add a high TF concentration (+ calcium ions); incubation time 1-2 min (37°C).

To study intrinsic thrombin generation you should add a high concentration of a contact trigger such as ellagic acid (+ calcium ions); incubation time about 4 min (37°C).

To study the procoagulant activity of plasma you should add only calcium ions (incubation time about 20 min at 37°C) or you could measure the amidolytic thrombin activity in EDTA/arginine plasma.

Best wishes

So you dislike the TGT with low TF ?

Thrombin generation is very important. It is so important that it should be tested with 4 approaches: extrinsic, intrinsic, just recalcification, systemic thrombin. If you add too much extrinsic or intrinsic trigger the assay might get blunted, e.g. there are many patients with hemostasis problems tested normal in PT or APTT. We should learn from blunted PT/APTT and establish thrombin generation assays without this problem. If we work with a too low TF concentration the extrinsic assay also depends from intrinsic factors.