Clinical Lab Handbook

Container/Tube: SST

Alternate: Mint Green (lithium heparin)

Collection Instructions: Centrifuge specimens and remove the serum or plasma from the cellular material within 4 hours of collection.

Rejection Criteria: Hemolyzed specimens. Hemolysis produces elevated phosphorus values due to the inorganic phosphates and phosphatases present in red blood cells.

The VITROS PHOS Slide is a multilayered, analytical element coated on a 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 and Subbarow. p-Methylaminophenol sulfate, an organic reductant reported by Gomori, reduces the complex to form a stable heteropolymolybdenum blue chromophore.

A drop of patient sample is deposited on the slide and is evenly distributed by the spreading layer to the underlying layers. 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, is distributed throughout the body. Causes of high serum phosphorus include dehydration, hypoparathyroidism, hypervitaminosis D, metastases to bone, sarcoidosis, pulmonary embolism, renal failure, and diabetes mellitus with ketosis. Low serum phosphorus is found in primary hyperparathyroidism and other causes of serum calcium elevation, sepsis, vitamin D deficiency, renal tubular disorders, chronic hemodialysis, vomiting, and occasionally with decreased dietary phosphate intake.

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