2. La presencia de la literatura en el espiritismo
2.2 El médium como base del trabajo del espiritismo
Due to the poor reproducibility and considerable inter-assay and inter-laboratory variability o f the VWFiRiCo assay there has been renewed interest in alternative assays for the measuring VWF function, in particular the use o f the VWFiCBA assay (Favaloro 1993; Fischer 1998; Favaloro 1999, Favaloro 2000b). Collagen types and source have been previously shown to be important variables in the performance o f the VWFiCBA. In this study a group o f 32 patients with previously characterised VWD and 22 controls were tested for VW FiCBA using type III collagen from human placenta, which has previously been shown to be sensitive to the loss o f HMW multimers (Favaloro 2000a).
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2
S . 1
2A CBA/Ag 2M CBA/Ag Control CBA/Ag
P a t i e n t a n d C o n tr o l G r o u p s
Figure 5.3.
Scatter plot showing VWF:CB A/VWF : Ag (CBA/Ag) ratio for type 2A and 2M VWD patients compared to the control group.S .
1.25 1.0 0- 0.75- 0.50- 0.25- 0.002A RCo/Ag 2M RCo/Ag Control VWF ROO/Ag
Patient and Control Groups
The VWF:Ag and VWFiRiCo assays were also tested in the same sample to allow a comparison between these assays. All three assays (VWFiAg, VW FiRiCo and V W FiCBA) were within the normal range in the control group reflecting the presence o f full binding o f VWF to GpIb-V-IX and VWF binding to human type III collagen, and thus normal levels o f fully functional HMW VWF.
All patients with type 2 VWD displayed disproportionately reduce VWF iRiCo/VWF iAg ratios and these patients would have been recognised as having a qualitative defect on the basis. This was an expected finding, as the VWFiRiCo assay, together with multimer and RIPA analysis, were originally used to identify and to classify these patients as detailed in Chapter 6.
Patients with type 2A VWD and the patient with type 2B VWD also displayed a disproportionately reduced V W FiCBAVW FiAg ratio. Thus, using the VW FiCBA these patients would have been correctly assigned as type 2 VWD with a defective VWF function. However, in contrast none o f the type 2M patients displayed an obviously reduced VW FiCBAW W FiAg ratio, as the ratio was either borderline or co n co rd ant. The use o f the VWFiCBA as a replacement for the VWFiRiCo assay would have led to these patients with type 2M VWD as being classified as type 1 VWD, or in the cases o f patients 10,19, 20, 21 and 22 as normal (Table 5.4 asterisked).
These data suggest that the VWFiCBA has been shown to detect qualitative defects associated with non-specific loss o f HMW multimers as present in type 2A VWD (where there is decreased synthesis or an increased proteolysis leading to the loss o f HMW multimers) and in type 2B VWD (where increased clearance o f HMW multimers occurs as a result o f increased reactivity o f platelets to VWF). However in the presence o f HMW multimers which define type 2M VWD, the VW FiCBA is purely a reflection o f the VWFiAg, as no differences between the VWFiCBA/VWFiAg ratios in controls and type 2M patients were observed. This is an important observation as not many cases o f type 2M VWD are described which is likely to be due to under-diagnosis o f this subtype and commonly mistaken for type 1 VWD as demonstrated in Chapter 6 (Sadler 1994; Hilbert 2000).
Despite the recognised limitations o f the VWFiRiCo assay, based on these findings, it appears that the VW FiCBA should not be considered a replacement for the VW FiRiCo assay. The two assays are not interchangeable as they measure different functions o f the VWF. Thus, as discussed in subchapter 5.1, VWFiRiCo assay measures the ability o f VWF to interact via Gplb to platelets on addition o f ristocetin, whereas the VW FiCBA is a direct reflection o f the presence o f HMW multimers and ability o f VWF to bind to collagen. Due to the multifunctional nature o f VWF no single functional assay could reflect the complete functional integrity o f the VWF protein. The use o f more than one functional test allows a fuller characterisation o f the abnormalities present in VWD. Although shown to be insensitive to type 2M VWD variants, the use o f the VW FiCBA in
combination with the VWFiRiCo assay may allow a more powerful and complete approach to the diagnosis o f qualitative variants.
In conclusion the VW FiCBA is a sensitive test in the diagnosis o f type 2A and 2B VWD but is o f limited use in discriminating type 2M VWD. The VW FiCBA therefore should not be considered a replacement for the VWFiRiCo assay, but rather as another useful diagnostic test in the profile o f VWD testing, enhancing the ability to determine functional variants in VWD.