To Estimate Sodium and Potassium
in Serum by Using Flame Photometer^36
36.1 Theory
Sodium is the major cation of extracellularfluid. Sodium is important for the
maintenance of osmotic pressure,fluid balance, and acid-base regulation. The
common salts used in cooking and food intake are the major sources of sodium.
The sodium is lost from the body via excretion through kidneys and excessive
sweating. About 50% of body sodium is present in bones followed by 40% in
extracellularfluid and 10% in soft tissues. Both extracellular and intracellular
sodium are the exchangeable form of sodium. The intracellular sodium contributes
about 10 mmol/L, and the extracellular form contributes about 135–145 mmol/L.
Sodium is also involved in normal muscle irritability, cell permeability, and mainte-
nance of heartbeat. In contrast to sodium, potassium is present mainly in intracellular
fluid. It is present majorly in RBCs (23 times higher than plasma). Like sodium,
excess potassium is also excreted by kidneys. Normal potassium concentration in
plasma is in range of 3.5–5.5 mEq/L. It is necessary for regulation of intracellular
osmotic pressure, water balance in cells, transmission of nerve impulse, etc.
36.2 Specimen Type, Collection, and Storage
Serum sample is used. Sodium and potassium present in serum remain stable for
several hours at 25– 35 C and for almost 3 months if stored at 20 C. Lithium
heparin may be preferred as an anticoagulant, but anticoagulants containing sodium
or potassium salts should be avoided. Hemolysis will increase potassium levels.
Dilute the standards and serum sample 1:100 using distilled water before use.
#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_36
147