Interlaboratory variability in multiplexed pneumococcal antibody testing

Abstract

This pragmatic, updated assessment of variability among pneumococcal antibody assays suggests that variability may now be greater than previously reported, and potentially influential in clinical decision making.

Figure 1.. Inter-laboratory correlation results for serotypes 4 (1a), 20 (1b), and 23F (1c).

X axis values represent pneumococcal IgG antibody levels (μg/ml) for laboratory A, with Y axis values representing antibody levels from laboratories B (open circle) or C (solid circle). Boxes show correlation coefficients (r) for each inter-laboratory comparison. There was strong correlation (r ≥0.70) across all three comparisons for only one serotype (serotype 4, Figure 1a). There was weak correlation (r ≤0.50) for all three comparisons for four serotypes (including serotype 20, Figure 1b). There was strong correlation between A and C, with weaker correlation for other comparisons for eight serotypes (including serotype 23F, Figure 1c).

Figure 2.. Protective versus nonprotective classification of pneumococcal IgG levels by different laboratories.

Individual measurements were categorized as nonprotective or protective on the basis of the specified thresholds, and are represented by red and green shaded boxes, respectively. Numbered rows represent serum samples, with columns representing serotypes. An asterisk to the right of a sample’s row indicates overall “protected” status for that sample (at least 70% of serotypes at or above the protective threshold). Empty boxes indicate three missing measurements from laboratory B (serotype 1 from two samples, and 15B from another), which was unable to analyze these serotypes due to a non-linear dilution response for those samples. 2a. Classification of pneumococcal IgG levels based on AAAAI criteria. A threshold of 1.3 μg/ml was used to categorize individual measurements as nonprotective (<1.3 μg/ml, red shaded boxes) or protective (≥1.3 μg/ml, green shaded boxes). 2b. Classification of pneumococcal IgG levels based on the WHO recommendations for pneumococcal vaccine evaluation. A threshold of 0.35 μg/ml was used to categorize individual measurements as nonprotective (<0.35 μg/ml, red shaded boxes) or protective (≥0.35 μg/ml, green shaded boxes).