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

Area of Science:

• Clinical Chemistry
• Analytical Biochemistry

Background:

• Discrepancies exist in serum inorganic phosphorus measurements using the SMAC (Sequential Multiple Analyzer Computer) method compared to other analytical systems.
• Accurate determination of serum inorganic phosphorus is critical for diagnosing and managing various metabolic and renal disorders.

Purpose of the Study:

• To investigate the cause of lower serum inorganic phosphorus concentrations observed with the SMAC method.
• To compare the performance of the SMAC method against other established methods for inorganic phosphorus determination.

Main Methods:

• Analysis of patient specimens using four different analytical systems: SMAC, AutoAnalyzer II, aca, and the Fiske-SubbaRow method.
• Conducting analytical recovery studies by adding known amounts of inorganic phosphorus to specimens.
• Statistical analysis to compare results and identify significant differences (p < 0.0001).

Main Results:

• The SMAC method yielded significantly lower serum inorganic phosphorus results compared to the AutoAnalyzer II, aca, and Fiske-SubbaRow methods.
• Analytical recovery studies demonstrated that the SMAC method recovered only approximately 87% of added inorganic phosphorus.
• A systematic error was identified, with SMAC results being 0.876 times the value obtained by the reference method.

Conclusions:

• The SMAC method exhibits a significant systematic error in determining serum inorganic phosphorus.
• This error is attributed to an inaccurate inorganic phosphorus concentration assigned to the SMAC calibration material by the supplier (Technicon).
• Clinical laboratories should be aware of this bias when interpreting SMAC results for inorganic phosphorus.