Of Normal Activity MONA method

The Multiple Of Normal Activity (MONA) method This procedure has the advantage of stepless titration and requires a single serum dilution only. Feigner (1978) considered an approximately parabolic relationship between the concentration of antibody and the absorbance to calculate the MONA. Unfortunately, one equation given for these calculations is incomplete here, a simple and more precise method (and example) is given for this useful MONA method. 

MONA can be defined as the number of times a serum should be diluted (D2) over that of the reference serum (D ) to obtain the same absorbance as the reference serum (= D2/D1). 

The absorbance of the various sera (diluted by the same factor) is determined after the EIA. A basic assumption of the MONA concept is that all dose-response curves are parallel. Each absorbance is, therefore, representative of a dose-response curve and, irrespective of the initial dilution, the factor of dilution is the same to obtain the same EIA-response for another serum (Fig. 15.9). This dilution factor (MONA = D2/D1) can be calculated with the slope m as shown in this Fig.  

For example, for the slope in Fig. 15.8. m = —0.4484. If EIA gives for this serum an absorbance of 0.30, for a more positive serum 0.50 and for a pool of negative sera 0.08, the MONA of the positive serum (/I = 0.30) is antilog [-(log 0.30/0.08)/-0.4484] = 19.06 and for the more positive serum 59.56. The MONA of the latter is 3.12 when calculated with respect to the less positive serum. These values are related by their product (19.06 x 3.12 = 59.56). This indicates that the choice of the reference serum (Normal Activity, MONA = 1) should be carefully made. The slope used here to calculate the MONA is related to the parabola exponent ( ) used by Feigner (1978) as m = —n.  

There are, however, also some important disadvantages since (i) it is assumed that dose-response curves are parallel, (ii) the determination of MONA is greatly influenced by the choice of the positive reference serum and, (iii) the range from which absorbance values are taken is only about half of the normal sigmoidal dose-response curve. 

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