Cheat Sheet for May, 2011

AMR and CCR for Coagulation Tests (May 1)

From Siddhartha Sharma: Can you please throw some light on the concept of AMR and CRR for coagulation testing instruments? Dr. Larry Brace responds that a CAP requirement is for each assay to have an established analytic measurable range (AMR) and a clinical reportable range (CRR). The AMR defines how high your assay can measure and still be reportable (linear) before making a dilution. The CRR is how high you want to report. AMR and CRR would need to be defined for each assay and instrument. PT Lisa Reid-Fifoot responds that laboratory directors are likely to dilute and report factor assay results but no one dilutes a PT or PTT. Most will just relay the instrument’s verbiage; for instance, greater than 300 seconds.

Prolonged PT, No Correction, Normal PTT (May 1)

“Annamaria09” describes a young man with a long PT that does not correct when mixed with PNP, his PTT is normal. Low HGB and elevated platelet count. He is not on coumadin or any other drugs. PTT 1:1 mix becomes prolonged. The patient was not bleeding, his fibrinogen is >800 mg/dL.

George discusses the possibility of a factor VII deficiency, liver disorder, an inhibitor secondary to bovine thrombin-based surgical fibrin glue, or a prothrombin-specific lupus anticoagulant.

Dave McGlasson suggests checking fibrinogen by running a thrombin time and a reptilase time. The patient could have a dysfibrinogenemia, which could be inherited or secondary to early liver disease.

PMorer asks is it is a real coagulation problem or PT interference? He has had personal experience with Endoxan prolonging only the PT. “Sutayl” asks, could it be an elevated VIII making the PTT normal but actually a positive lupus not correcting in the mixing study?

DIC Profile-Fibrin Monomer? (May 1)

Douglas Kolb’s DIC panel consists of platelet count, PT, PTT, Fib, FDP, and quant D-dimer (on TOP 500). He previously included the STAGO fibrin monomer qualitative slide test, should he continue?

George responds he may find the FDP is redundant to the quantitative D-dimer and less sensitive. He contends the fibrin monomer, and a sister assay, the thrombus precursor protein, are non-specific and less sensitive than D-dimer, and thus add nothing to the profile. Conversely, Gordon Ens advocates for the fibrin monomer as it may rise before the D-dimer and may be elevated in compensated chronic DIC.

D-dimer Vs. FSP (May 6)

Mohamed Emara asks, can the HS D-dimer test replace the FSP test? Why or why not? Also in pregnancy, since the D-dimer is always elevated, has any one tested and compared FSP levels?

George advocates for the quantitative D-dimer over the FDP (FSP) in all instances for its speed and accuracy. There is no real instance where the FDP provides information that amplifies the D-dimer. When using the D-dimer to diagnose and monitor disseminated intravascular coagulation (DIC), which is the primary application of the FDP assay, it is effective in all instances, as D-dimer elevations in DIC are profound and far exceed inflammation levels.

Shortened PFA Results (May 6)

Debbie Moffitt brought up a question regarding platelet testing with the PFA-100. Is a result shorter than the normal range normal or abnormal? Should we be concerned about a hypercoagulable state?

George knows of no published data correlating shortened PFA results with platelet hyperaggregability or thrombophilia, though the possibility is intriguing. The late Dr. E Mammen defined platelet hyperaggregability as an aggregation response to reduced ADP or epinephrine concentrations, but did not correlate these with PFA results.

In contrast to George’s response, Dr. Emanuel Favaloro commented that indeed, a short PFA-100 closure time has been proposed as a possible marker of thrombophilia, and will arise when (for example) there is a high level of VWF (or more likely a high level of high molecular weight VWF as for example measured by the collagen binding assay). He quotes two articles, the first has a section on the association of short PFA-100 closure times with thrombosis, and the second discusses the possible role of elevated VWF as a prothrombotic factor. He also mentions TTP as another good example of VWF-mediated thrombosis and suggests we should test patients with TTP with the PFA-100.

DTIs and the Fibrinogen Assay (May 8)

“Gagee” asks, do you know if dabigatran affects the fibrinogen levels like the other DTIs, argatroban, bivalirudin and lepirudin?

George answers, yes, but it isn’t that the DTIs affect the fibrinogen level, it is that they prolong the thrombin time, upon which the Clauss fibrinogen assay is based, giving the illusion of reduced fibrinogen. If we want an accurate fibrinogen concentration while using DTIs, we have to perform a fibrinogen immunoassay.

Joe Lamb commented, “So, should we add a disclaimer to our fibrinogen results that erroneously low results can be caused by DTIs?” George agrees and recalls Dave McGlasson saying the derived fibrinogen estimate, which several optical coagulometers report with every PT, is unaffected by argatroban, lepirudin, or bivalirudin.

PT Ratio? (May 14)

George posted a retrospective of a discussion in the comments attached to a September 18, 2008 post entitled Reference Intervals for Pediatric PTs. One of our active participants, “nomorefede” from Argentina supports the prothrombin time ratio (PTR) in place of prothrombin time in seconds with the PT is used for coagulopathy screening.

Prothrombinase-induced Clotting Test (May 16)

George describes CenterChem’s (PentaPharm) Pefakit prothrombinase-induced clotting test (PiCT). Samama MM and Guinet C, in Clin Chem Lab Med 2011;49:761-72, support the PiCT for monitoring fondaparinux, dabigatran, and rivaroxaban (with minor modifications). The PiCT has been available for at least ten years for monitoring standard unfractionated heparin and low molecular weight heparin.

Low Factor X, Normal PTT (May 19)

Vilas Hiremath has a patient with puberty menorrhagia. Her prothrombin time (PT) is prolonged, but corrected with normal pooled plasma (NPP). Her partial thromboplastin (PTT), thrombin time (TT), fibrinogen, FVII, and FV are all normal. Her factor X assay result is <1%, assessed using a PT-based assay. Since her factor X is deficient, why is her PTT normal?

Dave McGlasson has found that many PTT reagents are insensitive to low factor X activity levels, though any PTT reagent should give a prolonged result when factor X is 1%. He and George suggest that Vilas try another PTT reagent or try another factor X-deficient plasma reagent.

Steve Duff suggests adding a PTT-based FX assay using the in-house PTT reagent.

Vilas further commented that RVV activates factor X. He spiked the sample and performed a TEG. There is no correction; suggestive of factor X deficiency. He repeated with Echis carinatus and the TEG corrected to 0.3 mins, suggesting it does not require factor X to clot. Also, three different PTT reagents gave the same results. George responded that the Ecarin triggers coagulation at the prothrombin level. He echoes Steve Duff‘s suggestion to attempt a PTT-based factor X assay.

Changing Reagent Lots (May 25)

Cathy Labare is changing reagent lots for PTs and PTTs. How close should the normal ranges of the new lot be to the current normal range? George replies that UAB uses a limit of 10% but cautions to watch for trends. For instance, if last year the limits rose 7% and this year they rose 8%, you should change the range.

Nomorefede comments you always must change the curve for PT with least 20 samples to get a PPP. You obtain your 100% of activity and the reference values range from 70 (dilution) up to 120% (obtained by extrapolation). However with PTT you can test 20 healthy samples and if less than 3 exceed the manufacturers values it is permitted to uses the insert reference range.

Consumptive Coagulopathy (May 25)

“Sunny” asks if DIC and consumptive coagulopathy are the same. George replies these are synonyms for the same disorder. The term consumptive coagulopathy reflects the diminished coagulation factor activity typical of the condition, whereas DIC describes formation of microthrombi in capillaries and organs.

More on Low Factor X, Normal PTT (May 25)

Dr. Larry Brace responded to our May 19 discussion asking has anyone tested the parents? If this is an inherited X deficiency, both parents would need to be heterozygous in order to have a child that has 1% factor X. If both parents have normal X activity it must be assumed that the patient has an acquired X deficiency. There is a fairly long list of conditions that cause acquired X deficiency, but most would not be suspected in such a young patient. Also, test factor X by a chromogenic X assay. This would ameliorate the issue involved in different PT and PTT reagents used in most X activity assays. The patient should also be tested for factor X antigen.

Here is an additional comment from Vilas Hiremath on the same issue: PT is more sensitive than PTT for the detection of vitamin K-dependent coagulation factors like factor X.

George further responds, while it doesn’t answer Vilas’ question about why only the PT is affected, Dr. Brace’s suggestions can be used to confirm factor X deficiency. The unusual PT and PTT results make it necessary to reach a conclusion. George disagrees with Vilas’ assertion that the PT is more sensitive than the PTT for factor X and proposes both are equally sensitive, within the limits of their developers’ specifications.

Spontaneous Platelet Aggregation (May 30)

Gordon Ens returned to Debbie Moffitt’s discussion of shortened PFA closure times. He was reminded of the spontaneous platelet aggregation we observed many times at Colorado Coagulation Consultants. In some instances aggregation occurred immediately on beginning to stir the platelets in the aggregometer in the absence of any aggregating reagent. He asked if Debbie checked platelet aggregation in their patient?

Debbie responded on June 2 that her question was hypothetical. In the case of an extremely short PFA closure time an aggregation study would seem to be the appropriate follow-up if there was a question of hypercoagulability.

The Fritsma Factor