This technical note by Perkins describes a practical method for efficiently calculating geometric mean antibody titres from serological data. Antibody titrations require analysis of serum dilutions, and geometric mean titres provide useful summary statistics for groups of sera. However, manual calculation of these values is time-consuming and tedious. Perkins presents a 'ready reckoner'—a logarithmic lookup table containing base-10 logarithmic values of antibody titre reciprocals and their multiples (×3 through ×10). Users can consult this table to rapidly convert individual antibody titres to logarithmic values, sum them across multiple sera, divide by the number of samples to obtain the mean logarithmic value, then convert back to the arithmetic antibody titre. The author illustrates the method with a worked example of 20 sera with varying titres, demonstrating how the table reduces computational effort. This reference tool was intended to facilitate routine serological work in biological standards laboratories and other facilities performing frequent antibody quantifications.

Key findings

• A logarithmic lookup table ('ready reckoner') was developed to simplify calculation of geometric mean antibody titres from serological data
• The table contains base-10 logarithmic values of serum dilution reciprocals with multiples (×3 to ×10) for rapid reference
• The method reduces tedious manual calculations by allowing direct lookup and summation of logarithmic values rather than complex arithmetic
• The approach was demonstrated with a practical example of 20 sera with titres ranging from 8 to 2048