Quality issues in laboratory haemostasis

Abstract

Role of external quality assessment in the identification and resolution of assay problemsTests performed in coagulation laboratories play an essential role in the diagnosis and management of patients with familial and acquired bleeding and thrombotic disorders. It is therefore apparent that the generated results should be accurate, reliable and reproducible. This is particularly important in respect of tests undertaken to diagnose, or to exclude, a possible familial disorder.In recent years, there has been a marked increase in the workload and scope of the coagulation laboratory and this has been accompanied by the introduction of increasingly complicated automated equipment employing a variety of different techniques. It is apparent that the potential for error is considerable and for this reason it is essential that the performance of laboratories be monitored through its participation in an external quality assessment (EQA) programme.External quality assessment compares the results obtained from different laboratories on the same sample. It thus provides information in respect of the accuracy of results produced by individual participating laboratories.Participants in an EQA programme receive plasma samples from their EQA provider with instructions to perform specific tests using their usual method. It is important that the EQA samples are not passed on to senior laboratory staff but are tested by the same staff who normally perform the requested test or assay. The results are then returned to the EQA provider for detailed analysis. In most EQA programmes, the distributed samples are lyophilized. It is clearly extremely important that EQA providers ensure that results on the reconstituted lyophilized plasma are similar to those obtained on the native plasma.The assignment of target values for the distributed plasmas is an essential component of any EQA programme and for haemostasis; the overall consensus value is frequently adopted as the target value for EQA participants. However, this approach is not without its problems, particularly in the larger programmes where the number of different reagents, instruments and calibrants is extremely large with major differences being observed in the results obtained with different combinations. For this reason, it is more appropriate to assess results against the peer group median result. An assessment against the overall median is only considered appropriate where the number of laboratories deploying a single method with identical reagents is too small (<10) for statistical analysis or when different methods are known to give the same results.The assessment of laboratory performance by EQA providers is of utmost importance as it enables laboratories to compare their results against those obtained from other laboratories using the same reagents and the same methodology. The identification of unsuspected analytical problems allows laboratories to adjust their procedures and/or change their reagents or their calibrants.It is important for a laboratory to monitor itÕs pe...

Animal Models of Hemophilia

“…144 This latter knockout model has in fact been used to generate a number of additional strains each of which expresses a single copy F9 gene from the “socket” located in the endogenous single copy mouse F9 gene locus. These strains include: mouse FIX expressing a mutation that alters the FIX Gla domain interaction with endothelium (K5AFIX) 145 defective human FIX having a missense mutation at a critical arginine in the catalytic domain (R333QFIX) 146; 147 defective human FIX having a nonsense mutation in the Gla domain that results in an early stop mutation (R29XFIX) 148 human FIX wild type (FIX-WT mouse) 147 human FIX carrying three mutations each of which increases the specific activity of the protein (“FIX Triple”). 147 …”

“…defective human FIX having a nonsense mutation in the Gla domain that results in an early stop mutation (R29XFIX) 148 …”

“…To contrast with this, a mouse was created by homologous recombination into the F9 locus of a human FIX cDNA having a single nucleotide change that results in nonsense termination of transcription and a very early stop mutation (R29XhFIX mouse). 148 R29X is the most common mutation that leads to inhibitor formation in humans, as recorded in the database of hemophilia B mutations (Available at http://www.kcl.ac.uk/ip/petergreen/haemBdatabase.html. However, complete gene deletions lead to inhibitors with somewhat greater frequency than the stop mutation).…”

Influence of mechanical hemolysis of blood on two D-dimer immunoassays

“…The quality throughout the testing process is, however, essential for providing reliable and trustable information to the clinicians and thereby enabling safe rule out of an acute thrombotic episode. Reliable information suggests that the vast majority of errors in coagulation testing arises from the manually intensive activities of the preanalytical phase, rather than from analytical phase [4][5][6]. Among the various potential errors in the preanalytical phase, invitro hemolysis still represents the first cause of specimens rejection in laboratory diagnostics [7,8], including the coagulation laboratory where their prevalence is $1% of all samples and $20% of those considered unsuitable [9].…”

“…Among the various potential errors in the preanalytical phase, invitro hemolysis still represents the first cause of specimens rejection in laboratory diagnostics [7,8], including the coagulation laboratory where their prevalence is $1% of all samples and $20% of those considered unsuitable [9]. Although there is vast information about the influence of spurious hemolysis on clinical chemistry [7], immunochemistry [7], hematology [10], arterial blood gas [11], as well as conventional coagulation testing [4][5][6], less is known about the potential bias produced by in-vitro hemolysis on D-dimer testing to the best of our knowledge. Moreover, in none of the previous studies, the influence of spurious hemolysis has been assessed by producing a mechanical injury of blood to reproduce the effects of a troublesome venipuncture, as well as comparing simultaneously the effect on two different immunoassay techniques.…”