Figure 1. Artificially Low Ion Levels as Determined by Dilution-Based Methods. Normally, serum contains 7 percent solids by volume. In order to reduce the volume of blood needed for analysis, serum is frequently diluted before the actual measurement is obtained. The same volume of diluent is always used; the degree of dilution is estimated under the assumption that the serum contains 7 percent solid-phase particles. When the fraction of solid-phase particles is increased, the same amount of diluent results in a greater dilution, unbeknownst to the laboratory personnel (right side of figure). Consequently, the calculation of an ion level with the use of a degree of dilution that is based on the incorrect fraction of solid-phase particles will lead to an underestimate.