Phosphorus In Serum

Reference-interval

The Kodak Ektachem Clinical Chemistry Slide (PHOS) is a dry, multilayered analytical element coated on a clear polyester support.The analysis is based on the reaction of inorganic phosphate with ammonium molybdate to form an ammonium phosphomolybdate complex at acidic pH, as described by Fiske & Subbarow. p-Methylaminophenol sulfate, an organic reductant reported by Gomori, reduces the complex to form a stable heteropolymolybdenum blue chromophore.
The National Committee for Clinical Laboratory Standards identifies this method as preferred 'methodological principle' for the determination of serum inorganic phosphorus.
A 10 microliter drop of patient sample is deposited on the slide and is evenly distributed by the spreading layer. Phosphorus in the specimen forms a complex with ammonium molybdate. This complex is reduced by p-methylaminophenol sulfate to give a blue complex.
The concentration of phosphorus in the sample is determined by measuring the heteropolymolybdenum blue complex by reflectance spectrophotometry.

Phosphorus, as phosphate, has an ubiquitous distribution in the body. Most inorganic phosphate in the body is intracellular. Thus serum phosphorus concentration does not necessarily reflect total body phosphorous stores.
Serum phosphorous concentrations have a circadian rhythm, highest in the late morning, lowest in the evening. Serum levels are subject to rapid variation secondary to environmental changes. There is a seasonal variation with maximum levels in May & June & lowest levels in winter. Bed rest causes an increase in up to 0.5 mg/dL.

No special patient preparation is necessary.
Sample Preparation: Collect the specimen by the standard venipuncture technique. Lithium or sodium heparin may be used as an anticoagulant for plasma specimens. Sodium fluoride/ potassium oxalate, citrate, & EDTA should not be used as anticoagulants. Remove serum or plasma promptly from clot or cells. Handle specimens in stoppered containers to avoid contamination & evaporation. Refrigerate specimens at 2-8 degrees Celsius if analysis is not performed within four hours. Freeze specimens at -18 degrees Celsius if analysis is delayed beyond 48 hours.
Sample requirements: Minimum- 0.5 mL serum or plasma. Optimum- 1.0 mL serum or plasma.

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