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The use of RPPHS has resulted in a dramatic drop in A1AT AMCVs, while CVs for non-RPPHS-based RM actually continued to increase through 1996.
There was an initial increase in overall CVs, probably due to incorrect transfer of values from RPPHS by some manufacturers, although differences in antiserum reactivity with intact and fragmented Cp cannot be ruled out (see "Comment").
In some European QC programs, the introduction of RPPHS resulted in an initial increase in overall variance for Hp, followed by a fall to levels below those seen before RPPHS was introduced (data to be published).
Prior to the release of RPPHS, CAP introduced its own Reference Preparation for Serum Proteins 4 (RPSP-4), with values for most proteins assigned against the same materials subsequently used for RPPHS.
Several laboratories in the United States continue to use plasma protein values assigned against RMs not referenced to RPPHS, and some manufacturers continue to supply 2 sets of assigned values (RPPHS values and their own in-house values).
All RMs should be compared directly with RPPHS for all assay methods in which they are used, not only for a single instrument or method.
The value assigned for RPPHS, like those for a few other more recent RMs, is based on dry weight, amino acid analysis, and ultraviolet absorbance of very highly purified and well-characterized preparations of A1AT itself. As previously noted, free and complexed A1AT may react differently with different antisera or assay methods.
Although the C3 in RPPHS is completely converted to C3c (the more stable form), the assigned value is based on intact C3.
Again, the introduction of RPPHS has resulted in a marked narrowing of this among-manufacturer difference.
In the value transfers to RPSP-4 and RPPHS, however, only A1AT and Hp showed differences related to antisera, and those differences were minimal--in the range of [+ or -] 2% (unpublished data).
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