Several studies have evaluated the incidence of antigen excess in large numbers of consecutive patients. Murata et al.  studied 7,538 serum samples over a 4-month period using 1:100 and 1:400 sample dilutions on a Siemens BNII. There were nine samples with κ antigen excess but no samples with λ antigen excess giving an incidence of 1/840 (0.12%). Importantly, all the antigen excess samples had elevated FLC concentrations or abnormal κ/λ ratios at the initial dilution of 1:100 so they would not have been classified as normal. Bosmann et al.  studied the incidence of antigen excess in 91 patients. Samples from two patients (2.2%) exhibited antigen excess: one, a patient with λ FLC-monoclonal gammopathy of undetermined significance (Chapter 13) and the other, a κ FLC patient with a known IgAκ monoclonal gammopathy. The authors concluded that the interpretation of FLC measurements is facilitated in many cases, when combined with electrophoresis results and clinical information.
Vercammen et al.  studied the incidence of antigen excess in 865 patient samples using 1:100 and 1:2000 sample dilutions on a Siemens BNII. Antigen excess was defined as a greater than 4-fold difference between the results obtained at the two dilutions. This approach improves the consistency of reporting FLC values and is discussed further in Section 7.4.2 below. A total of 5.4% (44/811) and 1.2% (9/773) of κ and λ samples exhibited antigen excess respectively, which was much higher than that reported by others . A follow on study of 3,645 samples by the same group identified sample carryover by BNII cuvettes as a cause of false antigen excess . This phenomenon was reduced by batch analysis and the introduction of a cleaning and rinsing protocol, and the incidence of true antigen excess was recalculated as 0.25% and 0.03% for κ and λ sFLCs, respectively. Vercammen et al.  also reported that true antigen excess was not observed in samples with normal κ and λ sFLC concentrations.