Chapter 37

The Binding Site SPAPLUS is an automated, bench-top, batch mode turbidimeter with host interface capability, barcoded sample identification and reagent management systems (Figure 37.1). Precision is maintained through a combination of acid/alkali cuvette washing and an innovative reaction cuvette mixing system (Table 37.1). Air pressure is used in place of stirrers to mix the reaction mixture in a U-shaped cuvette. No physical contact is made with the reaction mixture, thereby removing any possibility of carry-over on a stirrer. Calibration curves are made from calibrator sets and validated by assay of control fluids supplied with the kits. Samples are initially measured at the standard programmed sample dilution and if out of range, the instrument automatically re-measures the samples at the appropriate alternative dilutions. All dilutions are made with the instrument’s pipetting system, which is capable of dilutions between 1/10 and 1/100. The assays include prozone parameters (Section 7.4). The instrument has a good overall performance compared with other analysers, and provides good throughput for patient samples in spite of its relatively small size.

κ sFLC λ sFLC
Range at 1/10 4.0 - 180.0 mg/L 4.5 - 165.0 mg/L
Sensitivity at 1/1 0.4 mg/L 0.5 mg/L
Assay time 15 min 15 min
Precision: within-run 3.3% at 7.2 mg/L 3.4% at 10.4 mg/L
1.6% at 35.7 mg/L 2.4% at 35.1 mg/L
1.8% at 123.8 mg/L 2.0% at 142.1 mg/L
Precision: between-run 4.2% at 7.2 mg/L 2.2% at 10.4 mg/L
1.9% at 35.7 mg/L 0.0% at 35.1 mg/L
2.3% at 123.8 mg/L 2.4% at 142.1 mg/L

Table 37.1. Freelite assay performance on the Binding Site SPAPLUS.

Antigen excess (prozone) parameters exist for IgMκ and IgMλ Hevylite SPAPLUS assays, and are discussed further in Section 11.4. Samples detected as being in antigen excess are automatically flagged by the instrument with a prozone (P) flag and the sample is automatically re-assayed at the higher re-dilution.