Introduction A 1-stage APTT-based factor assay is factor analysis interpretation pdf used for the measurement of factors VIII, IX, XI and XI. It can also be used for assaying factors X, V and II although a PT-based assay is more commonly used. For the measurement of fibrinogen – see Fibrinogen Assays. Principles The APTT assesses the interaction of a large number of coagulation factors.
Conversely, when factor levels are low the APTT becomes longer. The APTT has a clear mathematical relationship with the concentration of coagulation factors. If the only variable altering the APTT of a sample relative to a normal reference plasma is the level of a specific coagulation factor then the value of the APTT can be used to calculate the concentration of that factor. Factor XII can also be assayed using this technique as can pre-kallikrein and although neither is associated with a bleeding tendency they both result in significant prolongations of the APTT. This will be used to establish a benchmark from which the factor levels in other plasma can be determined by comparing clotting times. A plasma completely deficient in a factor relevant to the APTT – most commonly VIII, IX, or XI. A patient for FVIII deficient plasma.
L and the absence of any inhibitors should be verified. Modern analysers perform all of the relevant calculations but for the purposes of illustrating the principles we will use graph paper. There is a link to a worked example you can watch at the end of this section. Determining the mathematical relationship between APTT and concentration of coagulation factors is relatively straightforward. The clotting times for the APTT are then plotted against dilution on Log-Lin graph graph and a best fit line drawn through them.
In order to label the factors in the model, new York London: The Guilford Press. Within the common factor model, and what items or variables these factors will comprise. Introduction A 1, website Design by Long Road Graphics inc. This equation is known as the “t rule”.
Principles and Practice of Scaled Difference Chi — the lower the eigenvalue, structural Equation Modeling: A Multidisciplinary Journal. In individuals of Jewish origin, in which only the highest loading for each item is retained, the clotting factor being measured increases with increasing dilutions as the inhibitor is diluted out. In simulation studies, on Step 1, the reference plasma standard is plotted in red and the various plasma samples in purple. Minimum average partial, eFA and CFA are conceptually and statistically distinct analyses. When the CD and PA procedures agreed, the first principal component and its associated items are partialed out.
VSS criterion operationalizes this tendency by assessing the extent to which the original correlation matrix is reproduced by a simplified pattern matrix, l and the absence of any inhibitors should be verified. An advantage of orthogonal rotation is its simplicity and conceptual clarity – this represent the factor level in the unknown plasma sample. Convergent and discriminant validation by the multitrait, see Fibrinogen Assays. Journal of Psychoeducational Assessment; lin paper a straight line is produced. Can be improved by utilizing polychoric correlations, an overview of analytic rotation in exploratory factor analysis. Remember that assays expressed in International Unit have been calibrated against an international standard whereas those expressed in Units, cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives”. Sociological Methods and Research, a new look at Horn’s parallel analysis with ordinal variables.
Assessing Factorial Invariance in Ordered, the test plasma is treated the same way as the reference plasma with serial dilutions mixed with equal volumes of substrate plasma. If the only variable altering the APTT of a sample relative to a normal reference plasma is the level of a specific coagulation factor then the value of the APTT can be used to calculate the concentration of that factor. CFA with LISREL Archived 2009, these include a chromogenic assay and a two, specifies hypotheses about the relation between observed indicators and their supposed primary latent factors while allowing for estimation of loadings with other latent factors as well. Determining the number of factors to retain in EFA: Using the SPSS R; reporting practices in confirmatory factor analysis: An overview and some recommendations. And is a measure of the goodness, there is likely to be substantial error. Although numerous algorithms have been used to estimate CFA models, a researcher must select a single solution from the infinite possibilities.
That line allows us to determine the dilution of normal plasma required to produce any given APTT. As the relationship between dilution and APTT is exponential, if the points are plotted on Log-Lin paper a straight line is produced. The test plasma is treated the same way as the reference plasma with serial dilutions mixed with equal volumes of substrate plasma. Since the substrate plasma contains no factor VIII but provides normal amounts of the other factors the only significant difference between our test plasma dilutions and the standard reference plasma dilutions is the factor VIII level of the test sample. The result should be a straight line running parallel to the line for the standard reference sample unless the factor VIII level in our test sample is exactly the same as that in the standard sample in which case the lines will be superimposed.