Immunoglobulin G sub-class concentrations in South African adults: ethnic differences and reference ranges

Serum samples from healthy adult volunteers (n = 149) were selected at random from disputed paternity cases, laboratory staff and volunteers attending clinical trials. Total immunoglobulin G (IgG) and IgG sub-class (IgGSc) concentrations were determined by a radial immunodiffusion technique (RID). Standard statistical analyses were used to determine differences between groups. Reference ranges of IgGSc concentrations were calculated on the resultant groups of data. Total IgG and IgGSc concentrations in men and women of the same racial group were similar, except for IgG4 which was slightly higher in white males than in white females (median: 0.36 g/L vs 0.20 g/L respectively). IgGSc concentrations were higher in blacks than in whites (median values: IgG: 17.1 vs 12.1 g/L; IgG1: 11.1 vs 7.6 g/L; IgG2: 4.3 vs 3.2 g/L; IgG3: 1.2 vs 0.90 g/L respectively) with the exception of IgG4 which was similar in both groups (median: 0.29 g/L). It would appear that IgGSc values differ among the ethnic groups. Ethnicity must therefore be considered when calculating reference ranges. The reference ranges for the IgG sub-classes in the two ethnic groups are intended for use in our laboratory and in others in South Africa that use the RID technique.