Low results for inorganic phosphorus with the SMAC continuous-flow analyzer.

Serum inorganic phosphorus concentrations as measured with the SMAC are lower than those found with other methods. To resolve this problem we analyzed patients' specimens and performed analytical recovery studies with four different systems (SMAC, AutoAnalyzer II, aca, and the Fiske--SubbaRow method). With the SMAC, results for patients' specimens are significantly lower (p less than 0.0001) than with any of the other three methods. The SMAC recovered only about 87% of the added inorganic phosphorus. The value assigned to SMAC Reference I for inorganic phosphorus was 0.876 of the value obtained when the material was analyzed by the reference method. Thus there is a significant systematic error in the SMAC method for inorganic phosphorus determination, attributable to an erroneous inorganic phosphorus concentration assigned the SMAC calibration material by the supplier (Technicon).