Estimation of Inorganic Phosphorus
in Serum and Urine^22
22.1 Theory
The body contains about 800 g of phosphorus. Of this, 90% is present in bones, so it
is more widely distributed in the body than calcium. In the soft tissues, phosphorus is
present as organic form and incorporated into macromolecules. Phosphorous is also
present in some proteins, lipids, and nucleic acid and in some coenzymes. Phospho-
rus also plays a role in acid-base regulation of bodyfluids particularly by the
kidneys. The phosphorus of the blood is of four types:
- Inorganic phosphorus–the phosphates of alkaline and alkali earth metals, present
as H 2 PO 4 and HPO^24 - Organic or ester phosphorus–including glycerophosphates, nucleotide phos-
phate, hexose phosphate, etc. - Lipid phosphorus–present in lecithin, cephalin, sphingomyelin
- Residual phosphorus present in small amounts
Out of four types explained above, it is the inorganic phosphorus present in serum
which is measured. Phosphate in serum exists as both the monovalent and divalent
phosphate anions. The ratio of H 2 PO 4 and HPO^24 is pH dependent. About 10% of
phosphate in serum is bound to proteins; 35% is complexed with sodium, calcium,
and magnesium; and the remainder is free. Inorganic phosphate also forms major
component of hydroxyapatite in the bone, thereby playing an important part in
structural support of the body and providing phosphate for the extracellular and
intracellular pool.
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_22
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