Module 6: Calculate Concentrations

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Note: Although this software and accompanying documentation is dated 2004-2005, it is still valid in 2014. Questions can be sent to CDC-INFO.

Introduction

This module facilitates calculating antibody concentrations from patient serum samples and quality control samples. These concentrations may be arbitrarily assigned units (e.g., antibody units/ml), or mass values (e.g., µg/ml). A diagram used to illustrate the concentration calculations is shown in Figure 17. In this diagram, the absorbance is plotted on the logit-log scale to simplify the example. ELISA for Windows performs the actual calculations using the results of the more accurate four parameter logistic-log fit.

Figure 17 displays a rather idealized standard curve bracketed by two twofold serially diluted patient serum samples or unknown curves. For the purposes of this example, assume the antibody concentration of the standard reference serum (the calibration factor) is 135.8 micrograms/ml (µg/ml), and that the standard was initially diluted 1/100 with six subsequent twofold serial dilutions. This would lead to standard point 1 containing 1.358 µg/ml, point 2 containing 0.679 µg/ml, etc. The sample from Patient 1 was initially diluted 1/400 and that from Patient 2 was initially diluted at 1/25.