Maximising the diagnostic potential of <scp>APTT</scp>‐based screening assays for activated protein C resistance

Moore, Gary; Chege, Evelynn; Culhane, Aidan P.; Hunt, Beverley J.

doi:10.1111/ijlh.12419

Cited by 4 publications

(13 citation statements)

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“…Even if preliminary coagulation screening is normal, baseline clotting times of APC‐R assays (without added APC) should be checked, because elevated or reduced clotting times can invalidate calculated ratios . This is particularly important for assays without predilution, but should be undertaken for all ratio‐generating assays.…”

Section: Postanalytic Issuesmentioning

confidence: 99%

“…If patient plasmas are to be tested fresh or when frozen and thawed, cut‐offs should be derived from similarly treated donor plasmas. There can be a marked difference between the lower cut‐off of an RI and the range in which FVL‐positive individuals are found, particularly with predilution assays, leading to good separation between the results from normal individuals and the results from those with FVL . Some of the rare non‐FVL mutations of F5 conferring APC‐R tend to generate APC‐R results intermediate between those of wild‐type FV and FVL, whereas others generate APC‐R results similar to those of FVL .…”

Section: Postanalytic Issuesmentioning

confidence: 99%

“…Some of the rare non‐FVL mutations of F5 conferring APC‐R tend to generate APC‐R results intermediate between those of wild‐type FV and FVL, whereas others generate APC‐R results similar to those of FVL . Sex differences have been reported, although obtaining sufficient donors for separate ranges can be problematic, and combined ranges can be used. For children aged <6 months, a separate CAPC‐R RI is preferred, because ratios are higher than in adults, and the MAPC‐R assay has been shown to perform better with a 1:11 dilution .…”

Section: Postanalytic Issuesmentioning

confidence: 99%

“…The CAPC‐R assay is the most sensitive assay for acquired APC‐R, partly because elevated FVIII is a common cause . With acquired APC‐R, CAPC‐R ratios may be intermediate between RI and F5 mutation cut‐offs . Elevated FVIII can shorten baselines but indicate genuine acquired APC‐R .…”

Section: Postanalytic Issuesmentioning

confidence: 99%

“…Elevated FVIII can shorten baselines but indicate genuine acquired APC‐R . Performing the CAPC‐R assay alongside F5 mutation–specific assays has been advocated to additionally detect acquired APC‐R . Antibody‐mediated acquired APC‐R may manifest in predilution assays …”

Section: Postanalytic Issuesmentioning

confidence: 99%

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Recommendations for clinical laboratory testing of activated protein C resistance; communication from the SSC of the ISTH

Moore

Cott

Cutler

et al. 2019

Journal of Thrombosis and Haemostasis

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| INTRODUC TI ONRegulation of fibrin formation through activated protein C (APC) degradation of activated factor V (FVa) and activated FVIII is a major anticoagulant process of hemostasis. In 1993, Dahlbäck et al 1 identified thrombophilic individuals whose plasma showed a poor response to APC in a coagulation assay based on activated partial thromboplastin time (APTT). This was found to be related to an arginine 506 to glutamine substitution in F5 rendering FV resistant to APC inactivation, and called FV Leiden (FVL). 2 Mutations in F5 other than FVL that confer APC resistance (APC-R) with various degrees of clinical severity have been described, although they appear to be very rare. 3 As the original assay was based on APTTs performed on undiluted plasma, it was prone to numerous interferences, so a modification was subsequently proposed that improved sensitivity and specificity by diluting test plasma in FV-deficient plasma, and remains in widespread use. 4-6 Acquired APC-R may occur in the absence of F5 mutations, and represents an independent risk factor for venous thrombosis. 7 APC-R detection has evolved since the original assay and its modification, and this is the first guideline to address clinical laboratory testing recommendations for the wider set of commonly available phenotypic assays. | PRE ANALY TIC ISSUE S | Patient selectionIndiscriminate testing for APC-R is not recommended in unselected patients with venous thromboembolism (VTE). Targeted testing is recommended for those situations in which the results may give an indication of risk of recurrence and influence treatment, as is the case for any patient undergoing evaluation for thrombophilia involving VTE. More detail is available in recent clinical guidelines. 8-10 | Sample handlingVenous blood should be collected into a one-tenth volume of 3.2% (0.105-0.109 mol/L) trisodium citrate, and double-centrifuged to ensure a residual platelet count of <10.0 × 10 9 /L. 4,11,12 As some other thrombophilia assays also require similarly effective platelet removal, this permits running of multiple assays with the same, suitably prepared, plasma sample. The white cells remaining after plasma removal can be stored for DNA extraction should molecular analysis be required, or cells from an EDTA-anticoagulated sample can be used.Plasma for APC-R assays should be tested within 4 hours of collection or frozen (at -20°C if stored for ≤2 weeks, and at −70°C or below if stored for >2 weeks) if testing is postponed. Frozen samples should be rapidly thawed in a waterbath at 37°C, and thoroughly mixed by multiple, gentle inversions prior to testing. Icterus, hemolysis and lipemia can interfere, especially in assays performed on undiluted plasma. Plasma predilution assays are less affected by platelet contamination. 3 Preliminary coagulation screening is useful to detect previously unknown factor deficiencies and anticoagulation, and, if a suitably sensitive APTT reagent is employed, lupus anticoagulants (LAs) may also be detected. | InterferencesAssay design and reag...

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Section: Postanalytic Issuesmentioning

confidence: 99%

Section: Postanalytic Issuesmentioning

confidence: 99%