Figure 4.

Impact of selected serum components on test readout. (A) Nephelometry assay in the absence of serum. Spiking with fetuin-A delayed the transition from primary to secondary CPPs. and decreased RNU. NaCl indicates a reference precipitation curve without spiking. (B) Nephelometry assay in the presence of serum. Note that fetuin-A, albumin, and magnesium inhibited and lysozyme, phosphate, and calcium promoted precipitation. The red, nonspiked reference curve is the pooled serum from healthy volunteers. (C) Alternative presentation of T₅₀ and RNU₅₀ values taken from Figure 4B. Minerals mainly influence T₅₀, whereas proteins influence both T₅₀ and RNU₅₀. Quantities spiked in A and B: fetuin-A: 0.0625, 0.125, 0.25, 0.375, and 0.5 g/L (normal serum concentration is about 0.5 g/L); albumin: 3.125, 6.25, 12.5, 25, and 50 g/L (normal serum concentration is 35–52 g/L); lysozyme: 3.125, 6.25, 12.5, 25, and 50 g/L (normally not present in serum); Ca²⁺: 0.25, 0.75, 1.0, 1.5, and 2.0 mmol/L (normal serum concentration is 2.1–2.55 mmol/L); PO₄: 0.25, 0.75, 1.0, 1.5, and 2.0 mmol/L (normal serum concentration is 0.84–1.45 mmol/L); Mg²⁺: 0.25, 0.5, and 0.75 mmol/L (normal serum concentration is 0.75–1.0 mmol/L).