Characterization by image analysis of the dose vs response curve for a qualitative serum hCG lateral flow immunoassay

Background: As an adjunct to verification of performance characteristics of a qualitative serum hCG lateral flow immunoassay (LFI), we performed image analysis to characterize the dose vs response curve (visibility of the test line), as a means of understanding the transition from negative to positive as a function of increasing [hCG].Methods: Using serum samples of known [hCG], device images were obtained using a scanner at the prescribed reading time (5 min). Image analysis (using Python and R) was used to obtain the integral (S) of the test-line color as a function of [hCG].Results: Data for S as a function of [hCG] were well characterized by a simple hyperbola: S = Smax [hCG]/ ([hCG] + K), where K = 202 mIU/ml (r = 0.997). Replicates of S at K had CV of 7.3 %. By eye, uncertainty of test results among users occurred only below the assay's stated sensitivity of 10 mIU/ml, in region of S < 3 % of Smax, and signal:noise ratio < 3.Conclusions: By image analysis, the dose vs response (Test line integral) for this qualitative serum hCG LFI was a simple hyperbola. Characterization of the dose vs response curve was useful in verification of the assay's per-formance characteristics.

Automated summary

We used image analysis to characterize the dose vs response curve of a qualitative serum hCG lateral flow immunoassay, which helped us understand the transition from negative to positive. The results showed that the curve could be described by a simple hyperbola equation, which was useful for verifying the assay's performance characteristics.