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The interpretations below are provided by Donna Castellone, MS, MT (ASCP) SH for Aniara Diagnostica.

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Since 2020 meeting in person has been a challenge, so being able to attend a conference is truly an exciting opportunity. There is nothing like hearing a lecture, seeing vendors and interacting with peers that are involved in coagulation. I was lucky enough to be part of this meeting in Chicago and would like to highlight some of what was presented in regard to bleeding disorders and some recommendations on new testing. The lectures were informative and interesting, and so was Chicago!

BLEEDING DISORDERS

Acquied Inhibitors

A review of bleeding disorders discussed immune mediated factor deficiencies. Acquired inhibitors are rare and are suspected in people without a family history and an incidence of bleeding, a prolonged PT and or aPTT without a correction as well as the presence of a specific factor deficiency. Occurrences of an acquired factor X deficiency occur in younger children due to a viral infection. Factor II acquired inhibitors are seen in autoimmune diseases, most commonly Lupus. Factor VII inhibitors appear idiopathic occurring at a 2:1 ratio of males to females with a mean age of 38 years. Factor XIII inhibitors occur mostly after the age of 50 with heavy bleeding and can be treated with FXIII concentrate, while Factor V inhibitors occur at ages over 65 resulting in soft tissue bleeds and can be treated with platelets. It has been well documented that Hemophilia A, Factor VIII acquired inhibitors occur most frequently in the elderly and post-partum with up to 50% having a severe bleed and a 20% mortality rate. Emicizumab has also been used off label in acquired hemophilia. In all acquired inhibitors the objective is to stop the bleed, to irradicate the inhibitor with steroids and to treat the underlying disease.¹

Evaluation of Bleeding Disorders:

There are significant differences in clot firmness. Using a technique known as "integrated quasi-static acoustic tweezing thromboelastometry" (i-QATT™), a single drop of blood is forced to levitate and deform by the acoustic radiation force. Coagulation-induced changes in drop turbidity and firmness are measured simultaneously at different instants. The parameters describing early, intermediate, and late stages of the coagulation process are evaluated from the resulting graphical outputs. This method can rapidly detect hyper and hypo coagulable stated as well as single factor deficiencies in factors VII, VIII, IX, XI and XIII. Fibrinogen demonstrated a linear relationship with concentration and iQATT parameter of clot firmness and fibrin level. All results correlated with the gold standard tests and is suited for POC testing in patients with anemia and pediatric patients since it requires a capillary blood sample.²

Von Willebrand disease (vWD) is the most common bleeding disorder and may occur in up to 1% of the general population. It occurs to due a deficiency and or defect of vWF. Several guidelines require different recommendations for testing. The combination of tests used are different in several of the recommendations but does require a minimum of 3 tests. The testing itself is variable and can have poor sensitivity in the lower level that can compromise their utility. Most laboratories provide a Factor VIII activity, vWF antigen assay and vWF activity assay. Traditionally, the ristocetin cofactor activity was performed as the activity assay, however there are newer options available.

The ristocetin cofactor assay uses platelets and ristocetin to measure platelet agglutination. The newer assays are the ristocetin-based assays using recombinant GPIb (VWF:GPIbR), or non-ristocetin based assays using gain-of-function (mutant) (recombinant) GPIb (VWF:GPIbM). A VWF:GPIbB performed using latex or magnetic particles, recombinant GPIb, plus ristocetin to respectively measure latex agglutination or chemiluminescence based events.³

The VWF:GPIbM is performed using a latex agglutination assay in which the platelets that were previously used in the ristocetin cofactor assay are replaced with latex and the native GP1b used in the vWF cofactor is replaced with a gain of functon recombinant GP1b, there is no ristocetin in this assay. This provides reduced assay variation and better detection at the low level as well as being unaffected by vWF poly morphisms that are seen in the ristocetin assay. This can be associated with false diagnosis of type 2A or 2M, but the GP1bM assay may yield falsely high result in type 2B as well as being more expensive. This test may work better in your laboratory to aid in the diagnosis of vWD.³

A deficiency of Factor XIII is found in impaired wound healing as well as recurring miscarriages. This deficiency is caused by autosomal recessive mutations, acquired deficiencies may be due to autoimmunity. FXIII is fibrin stabilizing factor can is responsible for the crosslinking between fibrin monomers and between α2-antiplasmin and fibrin.

Laboratories most commonly used the clot solubility assay to evaluate the stability of crosslinked fibrin. The procedure adds calcium to citrated plasma allowing a clot to form. A protein denaturing reagent (urea, acetic acid or monoacetic acid) is added. Cross linked fibrin is stable and resistant to denaturation, but if uncrosslinked fibrin is present if denatures and redissolves into solution. This problem with this assay is that it is unstandardized and can only detect severe deficiencies. It is also dependent on fibrinogen levels. Quantitative assay have been developed based on two actions of FXIII: the transglutaminase activity and the isopeptidase activity.

The spectrophotometric ammonia release assay is a kinetic assay that is based on the quantification of ammonia as an indirect measurement of transglutaminase activity. This is based upon ammonia-dependent NADH and NADPH reduction. However they are other ammonia producing biochemical reaction found in plasma and may interfere with the accurate determination of FXIIIa transglutaminase activity. This can be corrected by plasma blanking in the presence of iodoacetamide (a potent FXIII antagonist). In the absence of these blanking procedures, ammonia-release assays are prone to FXIIIa activity overestimation.

CONCLUSIONS:

There are always new developments in the laboratory as well as updates in testing. Staying updated and aware of these tests can aid in the diagnosis of patients.

REFERENCES:

1. Diagnosis of bleeding disorders, THSNA Chicago, April 2024
2. Luo, D., Chelales, E.M., Beard, M.M. et al. Drop-of-blood acoustic tweezing technique for integrative turbidimetric and elastometric measurement of blood coagulation. Anal Bioanal Chem 413, 3369–3379 (2021)
3. Favaloro EJ, Pasalic L. Laboratory diagnosis of von Willebrand disease in the age of the new guidelines: considerations based on geography and resources. Res Pract Thromb Haemost. 2023 Jun 30;7(5):102143.
4. Durda MA, Wolberg AS, Kerlin BA. State of the art in factor XIII laboratory assessment. Transfus Apher Sci. 2018 Dec;57(6):700-704