Maintaining batch-to-batch consistency is essential as HLC assays may be used for monitoring individual patients over many years. The key component of any turbidimetric or nephelometric immunoassay is the polyclonal antisera. Therefore, it is essential to minimise any change in the specificity and performance of the antisera over time.
In order to ensure consistency between batches of polyclonal antisera, a virtual “rolling pool” of antisera has been established. This pool consists of a list of pre-approved antisera (Section 9.3 explains how suitable antisera are identified). During the manufacture of a batch of reagent, an equal portion of each approved antiserum from the list is mixed. As individual antiserum volumes vary, stocks become exhausted at different times. When this occurs, the antiserum is replenished with a new pre-approved antiserum. The pool of polyclonal antisera used in the manufacture of HLC assays always contains at least 90% of the same constituent antisera as the previous batch of reagent. The use of rolling pools of antisera during HLC assay manufacture has minimised batch-to-batch variation whilst ensuring a full range of HLC epitopes are recognised. Batch-to-batch variation is further discussed in Section 9.7. For IgM HLC assays, once a pool of suitable polyclonal antisera is made, sheep antibodies are attached to latex particles (in order to enhance their performance in nephelometric and turbidimetric immunoassays).