Quality of factor XI activity testing in North American Specialized Coagulation Laboratories.

INTRODUCTION: The performance of factor XI activity (FXI) by laboratories in the North American Specialized Coagulation Laboratory Association proficiency testing program was analyzed. METHODS: Over 10 years (2003-2013), 80 samples were distributed; 33-55 laboratories participated per exercise providing 3833 total responses. Analysis was performed on numeric results and qualitative classification of results. RESULTS: The sample FXI levels ranged from 3.8 to 154.0 IU/dL. The overall interlaboratory average coefficient of variation (CV%) was 17.5%; the CV was higher for a sample with low (3.8 IU/dL) FXI. Results were correctly classified as abnormal (100%) for a sample with 3.8 IU/dL FXI and normal/borderline normal (97.7%) for 45 samples with 80 to < 140 IU/dL FXI. The classification was heterogeneous for samples with FXI of 50 to < 80 IU/dL. Six specimens were repeat-tested from 2007 to 2013. The mean FXI was not significantly different in laboratories using the same method on both exercises, suggesting good intralaboratory precision over time. Univariate analysis of data from 2011 to 2012 did not find a consistent significant difference among the activators, analyzers, calibrators, and FXI-deficient plasmas. CONCLUSION: Laboratories generally performed well in assessment of FXI based on interlaboratory precision when FXI >30 IU/dL and on classification of samples with very low or normal FXI.

Factor VII assay performance: an analysis of the North American Specialized Coagulation Laboratory Association proficiency testing results.

The performance of factor VII (FVII) assays currently used by clinical laboratories was examined in North American Specialized Coagulation Laboratory Association (NASCOLA) proficiency tests. Data from 12 surveys conducted between 2008 and 2010, involving 20 unique specimens plus four repeat-tested specimens, were analyzed. The number of laboratories per survey was 49-54 with a total of 1224 responses. Numerous reagent/instrument combinations were used. For FVII > 80 or <40 U/dL, 99.5% of results (859/863) were correctly classified by laboratories as normal/abnormal. Classification of specimens with 40-73 U/dL FVII was heterogeneous. Interlaboratory precision was better for normal specimens (coefficient of variation (CV) 10.7%) than for FVII<20 U/dL (CV 33.1%), with a mean CV of 17.2% per specimen. Intralaboratory precision for repeated specimens demonstrated no significant difference between the paired survey results (mean absolute difference 2.5-5.0 U/dL). For specimens with FVII >50 U/dL, among commonly used methods, one thromboplastin and one calibrator produced results 5-6 U/dL higher and another thromboplastin and calibrator produced results 5-6 U/dL lower than all other methods, and human thromboplastin differed from rabbit by +7.6 U/dL. Preliminary evidence suggests these differences could be due to the calibrator. For FVII <50 U/dL, differences among the commonly used reagents and calibrators were generally not significant.

Evaluation of the i-STAT point-of-care capillary whole blood prothrombin time and international normalized ratio: comparison to the Tcoag MDAII coagulation analyzer in the central laboratory.

BACKGROUND: Point-of-care devices for performing a prothrombin time/international normalized ratio (PT/INR) using capillary blood samples are being increasingly used to monitor patients receiving anticoagulation therapy. However, the performance of some devices has been shown to be suboptimal and there are only limited published data comparing specific devices to various central laboratory coagulation analyzers. We report an evaluation of the iSTAT PT/INR with a comparison to the Tcoag MDA II analyzer. METHODS: We obtained simultaneous capillary/venous samples on 20 healthy volunteers for a normal range study and on 50 anticoagulated patients for a clinical evaluation. Testing was performed by phlebotomists. We also obtained 68 near simultaneous capillary/venous test results for assessment of performance by non-laboratory personnel. The criteria for determining clinical equivalence of the iSTAT to the MDA II were (1) same clinical category (subtherapeutic INR<2, therapeutic INR 2-3, and supratherapeutic INR>3) or (2) paired values within ≤ 0.4 INR. RESULTS: Forty nine of 50 patient sample pairs collected by phlebotomists showed acceptable clinical agreement. Sixty one (61) of 68 patient sample pairs collected by nurses showed acceptable agreement. In all discordant cases the differences were minor and would have resulted in either no or minimal change in therapy. CONCLUSIONS: The iSTAT PT/INR compares well to the MDA II when performed by phlebotomists or nurses.

Coagulation point-of-care testing.

With PT point-of-care devices, further study is needed to fully evaluate the safety and efficacy regarding home self-monitoring of oral anticoagulant therapy. Point-of-care PTT testing is also undergoing evaluation. In contrast, the ACT is commonly in use, despite its limitations, at least partly because of the lack of a readily available, inexpensive alternative with sufficient turnaround time. Several platelet function point-of-care devices have also become available, but their role in clinical care is not yet well defined.

The pool of fatty acids covalently bound to platelet proteins by thioester linkages can be altered by exogenously supplied fatty acids.

The goals of this investigation were, first, to develop a chemical strategy to identify and quantitate the mass of fatty acid which is covalently bound to proteins by thioester linkage in unactivated platelets, and, second, to determine whether exogeneously added fatty acids can alter the fatty acid composition of thioester bound fatty acids. Studies with radiolabeled fatty acids cannot identify and quantitate the actual fatty acids bound to proteins because they permit analysis of only the radiolabeled fatty acids added and their metabolites. Therefore, in the absence of metabolic labeling by radiolabeled fatty acids, we isolated the thioester-linked fatty acids from platelet proteins using hydroxylamine at neutral pH to form fatty acid hydroxamates. The hydroxamates were subsequently converted to fatty acid methyl esters by acid methanolysis for quantitation by gas chromatography-mass spectrometry. Using platelet specimens from 14 subjects, 74% of the fatty acid recovered from the unactivated platelet proteins as thioester linked was palmitate. Importantly, however, 22% was stearic acid, and oleate was 4% of the total thioester bound fatty acid. There was minimal variability (2.6-fold at maximum) between the subjects in the amount of the thioester-linked palmitate and thioester-linked stearate. However, there was substantial variability (>100-fold at maximum) between subjects in the amount of thioester-linked oleate. We also demonstrated that incubation of platelets with exogenous fatty acids can alter the profile of fatty acids bound to platelet proteins by thioester linkages. Incubation of platelets with 100 microM palmitate for 3 h increased the amount of thioester-linked palmitate by up to 26%, and incubation of platelets with 100 microM stearate increased the amount of thioester-linked stearate up to 30%. In support of the observation that radiolabeled fatty acids other than palmitate were shown to be capable of binding to platelet proteins by thioester linkage, our results indicate that the fatty acids actually bound to unactivated platelet proteins include a significant amount of stearate, and variable amounts of oleate, as well as palmitate. In addition, the data show that palmitate and stearate can be increased, as a percentage of total protein-bound fatty acid, by incubation with exogenous palmitate and stearate, respectively.

College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: the clinical use and laboratory monitoring of low-molecular-weight heparin, danaparoid, hirudin and related compounds, and argatroban.

OBJECTIVE: To review the role of the laboratory in monitoring therapy with low-molecular-weight heparin, danaparoid, hirudin, and argatroban, as reflected in the medical literature and the consensus opinion of recognized experts in the field. DATA SOURCES: Review of the medical literature and current clinical practice by a panel of 6 international experts in the field of anticoagulant therapy. DATA EXTRACTION AND SYNTHESIS: The experts made an extensive review of the published literature and prepared a draft manuscript, which included preliminary recommendations. The draft manuscript was circulated to participants in the College of American Pathologists Conference XXXI on Laboratory Monitoring of Anticoagulant Therapy prior to the conference. The manuscript and recommendations were then presented at the Conference for discussion. Recommendations were accepted if a consensus of the 26 experts attending the Conference was reached. The results of the discussion were used to revise the manuscript into its final form. CONCLUSIONS: This report reviews the mechanism of action and potential uses of these newer anticoagulant agents. General guidelines for monitoring these agents and 9 specific recommendations for laboratory monitoring of low-molecular-weight heparin and danaparoid are provided, along with citation of the appropriate supporting literature. Issues for which a consensus was not reached at the Conference are also discussed.

Laboratory evaluation of hypercoagulable states.

The number of well-characterized hereditary and acquired hypercoagulable conditions is increasing, such that in many thrombophilic patients, the laboratory can now identify a hypercoagulable condition. This review describes the currently known hypercoagulable states that predispose patients to venous, and in some instances, arterial thrombosis. For each condition, the discussion includes the incidence, magnitude of the thrombotic risk in the general population in comparison with symptomatic families, synergistic interactions among the various hypercoagulable conditions, molecular pathogenesis, and interpretation of laboratory test results. In addition, recommendations for laboratory testing are summarized.

Vascular hemostasis in flowing blood in children.

This review considers differences in hemostasis among newborns, children, and adults from the standpoint of the vascular endothelium and, where appropriate, in the presence of flowing blood. Special procoagulant features of newborn hemostasis include unusually large von Willebrand factor multimers, augmented platelet transport under flow conditions, and greater ability of newborn endothelium to generate tissue factor. Special anticoagulant features in the newborn include increased vessel wall glycosaminoglycan activity, elevated alpha2-macroglobulin, and increased percentage of free protein S. The net effect of the differences is that hemostasis is generally achieved in all age groups but is developmental in nature. In addition to congenital hypercoagulable states and catheter placement, developmental vascular anomalies appear to constitute a thrombotic risk, at least in some children (and possibly adults).

Fatty acid acylation of platelet proteins.

A variety of fatty acids can become covalently attached to platelet proteins by thioester linkage. These fatty acids include palmitate, myristate, stearate, arachidonate, and eicosapentaenoate. More than 20 platelet proteins can be acylated by fatty acids. Several of the acylated platelet proteins have been identified, including glycoprotein Ib beta, glycoprotein IX, P-selectin, G-protein alpha subunits, and CD9. This report reviews the fatty acid acylation of platelet proteins.

Cloning and expression of the NaeI restriction endonuclease-encoding gene and sequence analysis of the NaeI restriction-modification system.

NaeI, a type-II restriction-modification (R-M) system from the bacterium Nocardia aerocolonigenes, recognizes the sequence 5'-GCCGGC. The NaeI DNA methyltransferase (MTase)-encoding gene, naeIM, had been cloned previously in Escherichia coli [Van Cott and Wilson, Gene 74 (1988) 55-59]. However, none of these clones expressed detectable levels of the restriction endonuclease (ENase). The absence of the intact ENase-encoding gene (naeIR) within the isolated MTase clones was confirmed by recloning the MTase clones into Streptomyces lividans. The complete NaeI system was finally cloned using E. coli AP1-200 [Piekarowicz et al., Nucleic Acids Res. 19 (1991) 1831-1835] and less stringent MTase-selection conditions. The naeIR gene was expressed first by cloning into S. lividans, and later by cloning under control of a regulated promoter in an E. coli strain preprotected by the heterologous MspI MTase (M.MspI). The DNA sequence of the NaeI R-M system has been determined, analyzed and compared to previously sequenced R-M systems.

Cloning the FnuDI, NaeI, NcoI and XbaI restriction-modification systems.

Methyltransferase genes from the FnuDI, NaeI, NcoI, and XbaI restriction-modification systems have been isolated in Escherichia coli by 'shot-gun' cloning bacterial DNA fragments into plasmid vectors and selecting for protectively modified molecules that resist digestion by the corresponding restriction endonuclease.

Cloning, sequencing and expression of the Taq I restriction-modification system.

The Taq I modification and restriction genes (recognition sequence TCGA) have been cloned in E. coli and their DNA sequences have been determined. Both proteins were characterized and the N-terminal sequence of the endonuclease was determined. The genes have the same transcriptional orientation with the methylase gene 5' to the endonuclease gene. The methylase gene is 1089 bp in length (363 amino acids, 40,576 daltons); the endonuclease gene is 702 bp in length (234 amino acids, 27,523 daltons); they are separated by 132 bp. Both methylase and endonuclease activity can be detected in cell extracts. The clones fully modify the vector and chromosomal DNA but they fail to restrict infecting phage. Clones carrying only the restriction gene are viable even in the absence of modification. The restriction gene contains 7 Taq I sites; the modification gene contains none. This asymmetric distribution of sites could be important in the regulation of the expression of the endonuclease gene.