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Phosphate – Serum Blood Test

Phosphates are salts of phosphoric acid H₃PO₄. Most phosphates (86%) are incorporated in the bone and form hydroxyapatite together with calcium. About 13% of the phosphates are intracellular constituents of macromolecules (DNA, RNA or ATP). Only a small proportion of the phosphates are dissolved extracellularly or intracellularly and have an important buffer function in the acid-base homeostasis. The phosphate level in the blood has a circadian rhythm (high in the morning) and is regulated by somatotropin, parathyroid hormone, glucocorticoids and sex hormones.

Standard value:

0,8–1.5 mmol/l.

Laboratory test method:

Spectrophotometry.

Indications:

Chronic kidney disease, kidney stones, bone diseases, parathyroid disorders, thyroid surgery, parenteral nutrition, malnutrition, alcoholism.

Differential Diagnosis of Hypophosphatemia:

Hypophosphatemia is a low concentration of phosphate in the blood. Below 0.35 mmol/l, phosphate deficiency leads to disruption of cell energy supply with muscle weakness, neurological symptoms, rhabdomyolysis, and hemolytic anemia. Causes include inadequate intake, alcohol abuse, antacids, malabsorption, vitamin D deficiency, hyperparathyroidism, hyperventilation and respiratory alkalosis, diuretics, insulin therapy for diabetic coma, fast carbohydrate intake in malnutrition or sepsis.

Differential Diagnosis of Hyperphosphatemia:

Hyperphosphatemia is a high concentration of phosphate in the blood with ectopic calcifications, secondary hyperparathyroidism and renal osteodystrophia. Causes are either too low excretion of phosphates (renal insufficiency, hypoparathyroidism, acromegaly, vitamin D overdose) or the release from the intracellular space due to cell death (acidosis, tissue hypoxia, chemotherapy, rhabdomyolysis, hemolysis, immobilization).

References

  Deutsche Version: Elektrolyte im Serum: Phosphate

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