Quasi quantitative assay

Quasi-quantitative assay does not involve the use of calibrators mostly due to the lack of suitable reference material, so the analytical result of a test sample is reported only in terms of the assay signal (e.g., optical density in ELISA). 

This chapter deals with the assessment of definitive and relative quantitative assays. A good reference on the analytical validation of a quasi-quantitative assay is a white paper on immunogenicity by Mire-Sluis et al. [6] and the guidance on assay development and validation for high-throughput screening developed by scientists from NIH and Eli Lilly Company [7]. 

Quasi-quantitative assays traditionally include measures of enzymatic or ligandbinding activity, as in flow cytometry and anti-drug antibody assays [9]. One of the common characteristics of these assays is the lack of a true reference standard, where reference standards are poorly characterized, do not completely represent native protein, or differ from native proteins in terms of potency or immunoreactivity. As stated above, if the analytical response is continuous across the range in question, the analytical results can be expressed in terms of a characteristic of known test samples. The following is one example an ELISA qualified as a quasi-quantitative assay because it could not be validated as a relative quantitative assay. 

Biomarker assays (as other bioassays) may be classified into definitive quantitative assays, relative quantitative assays, quasi-quantitative assays, and qualitative assays with varying degrees of validation requirements (Table 5.5-3) [14, 15]. For definitive quantitative assays, a well-defined or characterized standard of the biomarker is available. In the case of relative quantitative assays, calibration is performed with a standard that is not well characterized, not available in pure form, or not representative of the endogenous biomarker. Results from these assays are... 

Parameter Definitive Quantitative Assay Relative Quantitative Assay Quasi- Quantitative Assay Qualitative Assay... 

Assay Qualification for a Quasi-Quantitative Ligand-Binding Assay Used in Exploratory Biomarker Studies... 

Qualitative Versus Quasi-Quantitative LBA Assay Formats... 

As a result of the quasi-quantitative nature of anti-drug antibody immunoassays and the lack of a reference standard a threshold value, the so-called cutoff or cutpoint is used to identify positive samples from nonspecific background noise. The assay cutoff is preferably determined by analyzing samples from healthy individuals and those affected by the disease. The data are subsequently used to... 

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