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Serum Electrolytes
1. Estimation of Sodium &
Potassium
Ashikh Seethy
Senior Resident
Department of Biochemistry
2. Objectives:
At the end of this briefing, you should be able to describe:
The distribution of Na+, K+ and water in the body.
The role of Na+ and K+ in maintenance of homeostasis.
The different pathological conditions in which Na+ and K+
balance is disturbed.
Various techniques utilized for estimation of serum Na+ and
K+.
3. The Body as Organized
“Solutions”
In the body of a young adult male:
Proteins:18%
Minerals: 7%
Fat: 15%
Water: 60%
4. Fluids Compartments:
Total Body Water: 42 L
Intra-cellular
Fluid
28 L
66%
Extra-
cellular
Fluid
14 L
34%
Interstitial
Fluid
10.5 L
Plasma
3.5 L
6. Osmolality:
Measure of the number of osmotically active particles in
serum.
Calculated serum osmolality = (2 x serum Na+) + Glucose +
Urea
(in mmol/L).
Estimated in lab by Osmometer (based on colligative
properties).
Reference interval: 275–295 mOsmol/kg of water.
7. Water Balance is Regulated by the
Hypothalamus, the Neurohypophysis and the
Kidneys
9. Water and electrolytes can be lost through
Gastrointestinal tract
Skin
Bronchial tree etc.
But kidneys are the only organs able to conserve or excrete
electrolytes and water under tight regulatory control.
13. Sodium:
Principle cation of ECF
Reference interval (Plasma): 136 to 145 mmol/L
Recommended daily dietary intake : < 2 g (<5 g salt)
Na+ levels are regulated by the kidneys
Functions:
Maintains normal water distribution and osmolality
Maintenance of membrane potential
Absorption of chloride, amino acids, and glucose
15. Hypernatremia
ECF Volume
Increased
• Total body water↑
• Total body
sodium↑↑
Not Increased
• Total body water↓↓
• Total body sodium↓
Hypertonic NaCl
NaHCO3
Insensible water loss
GI water loss
Central Diabetes Insipidus
Nephrogenic Diabetes
Insipidus
Osmotic Diuresis
16. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↑
Total body sodium
↔
• Hypervolemia
• Total body water↑↑
Total body sodium ↑
UNa> 20 UNa< 20
17. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↑
• Total body sodium
↔
• Hypervolemia
• Total body water↑↑
Total body sodium ↑
UNa> 20 UNa< 20
Renal losses
Diuretics
↓↓
Minerallocorticoids
Osmotic diuresis
Metabolic alkalosis
18. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↑
• Total body sodium
↔
• Hypervolemia
• Total body water↑↑
• Total body sodium ↑
UNa> 20 UNa< 20
Renal losses
Diuretics
↓↓
Minerallocorticoids
Osmotic diuresis
Metabolic alkalosis
Extra-renal losses
Vomiting
Diarrhea
Trauma
Pancreatitis
19. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↓
• Total body sodium
↔
• Hypervolemia
• Total body water↑↑
Total body sodium ↑
UNa> 20 UNa< 20
Nephrotic
syndrome
Cirrhosis
Cardiac failure
Acute Renal Failure
Chronic Renal
Failure
20. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↑
• Total body sodium
↔
• Hypervolemia
• Total body water↑↑
Total body sodium ↑
Una> 20
Glucocorticoid
deficiency
Polydipsia
SIAD- Syndrome of
Inappropiate
Antidiuresis
21. Hyponatremia
Volume
Status
• Hypovolemia
• Total body water↓
• Total body sodium
↓↓
• Euvolemia
• Total body water↑
• Total body sodium
↔
• Hypervolemia
• Total body water↑↑
Total body sodium ↑
• Total body water ↔
• Sodium intake↓
Beer potomania
Nutrient restricted diet
22. Potassium:
Principle intracellular cation (140 mmol/L)
High cellular concentrations maintained by active transport
mechanism via Na+/K+ ATPase pump
Reference interval (Plasma): 3.5 – 5.0 mmol/L
Normal daily dietary intake : at least 90 mmol/day (3510
mg/day)
Functions:
Maintenance of ionic gradients which is required for:
• Nerve impulse transmission
• Muscle contractility
26. Sample Considerations:
Serum, heparinized plasma or whole blood may be used for
Na+ estimation
Whole blood or heparinized plasma preferred for K+
Samples should be maintained near 25 °C
Preferably plasma to be separated by high speed
centrifugation without cooling
Hemolysis to be avoided
Avoid prolonged tourniquet use and fist clenching
27. Techniques for Estimation of Na+ and
K+
Ion selective electrode (ISE)
Atomic absorption spectroscopy
Flame emission photometry
29. Flame Emission Photometry
The intensity of emission is proportional to the number of
excited atoms, which is indeed proportional to the
concentration of the element in the solution.