Standard Curve Fitting Model Not Appropriate (ELISA (Standard Curve Fit Problems))

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The recommended curve-fitting model (typically Four-Parameter Logistic) does not adequately fit the standard data points, resulting in poor correlation even with properly prepared standards. Common causes: 1) Assay dynamic range characteristics do not match Four-Parameter Logistic (4PL) model assumptions 2) Standard curve exhibits linear behavior in the working range rather than sigmoidal response 3) Five-parameter logistic (5PL) model may be needed for asymmetric sigmoid curves 4) Residual pipetting errors or replicate variation masking appropriate model selection Solutions: 1) Always follow manufacturer's instructions for curve-fitting model in the first instance 2) If recommended model fails, systematically test alternative models: linear, 4PL, or 5PL 3) Verify that poor fit is not due to replicate variation by examining coefficient of variation (CV%) between duplicates/triplicates 4) Confirm pipetting accuracy by re-running standards with meticulous technique before changing curve model 5) Consult ELISA kit datasheet for acceptable R² values and curve shape examples specific to the assay