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Molality is the number of moles of osmotically active substances in 1 kg of solvent. The presence of osmotically active substances in the plasma (sodium and chlorine ions, non-protein nitrogen, glucose) determines the movement of water and ions through semipermeable cell membranes, causing the movement of electrolytes inside the cells or in the opposite direction.
What is plasma molality?
The molality of the plasma is the measure of the number of substances dissolved in the serum. It is very influenced by sodium, which, next to potassium, chloride and bicarbonate ions, is responsible for maintaining the proper acid-base balance of our body. The kidneys are involved in regulating the plasma molality. Simultaneously with lowering the sodium level, the osmolality decreases (hyponatremia), and vice versa, when sodium increases (hypernatremia) – the osmolality increases. Another substance that influences osmolality is glucose, which determines the movement of water between the extracellular and intracellular water space.
Note: Hyponatraemia (lowering sodium levels) can occur in marathon runners because they consume large amounts of water in a short time. Sometimes this condition leads to the death of the athlete. In contrast, chronic hyponatraemia can affect people who, by choice or for other reasons, drink excessive amounts of water for a long time.
When do we do plasma molality?
Plasma molality is performed in the following cases:
1. In unconscious sick people.
2. When ketoacidosis or lactic acidosis is suspected.
3. Poisoning with toxins and alcohol (methanol, ethylene glycol).
4. Dehydration.
5. Water and electrolyte disturbances (monitoring, assessment of its disturbances).
6. Kidney failure.
7. Monitoring treatment with substances that are osmotically active.
8. Suspicion of chronic diarrhea caused by the presence of osmotically active substances.
In addition, the osmolality test is determined in a patient with suspected hyponatraemia, which is manifested by:
- bottom,
- headaches
- nausea
- excessive thirst,
- confusion.
Plasma molality – study
Osmolality test material: plasma.
Preparation for the test: on an empty stomach (at least 8 hours).
The course of the plasma molality test: one-time blood sampling from a vein in the arm. The received sample is sent for further analysis.
Time to wait for the result: 1 Day.
Standard: 280-295 mmol / kg water.
Comments: A reduction in osmolality most often indicates a reduction in sodium levels in the body. On the other hand, an increase in osmolality indicates disturbances in carbohydrate metabolism (in diabetes) or kidney function, or – an increase in sodium concentration.
Plasma molality – interpretation of results
Plasma molality is a very dynamic feature that changes along with temporary disturbances in the fluid and electrolyte balance. Therefore, when interpreting the test result, the patient’s general condition and the results of other tests (urea, glucose, sodium) should be taken into account. The sole determination of molality does not provide a basis for a final diagnosis, it only indicates some disturbances in the patient’s water balance.
1. Increase in plasma molality is observed in such cases as:
- condition after drinking alcohol,
- hyperglycemia (there is a significant increase in glucose that affects serum osmolality),
- hypernatmia, i.e. an excess of sodium occurring in the course of, among others, nephrogenic diabetes insipidus, central diabetes insipidus, vomiting and diarrhea,
- hyperglycemic uncetone coma,
- treatment with mannitol.
2. Drop in plasma molality may be associated with sodium deficiency (hyponatraemia), which occurs in the following conditions:
- kidney problems,
- nephrotic syndrome,
- overhydration
- adrenal insufficiency,
- SIADH (syndrome of inadequate secretion of vasopressin) – in the course of this disease, vasopressin is released by the posterior pituitary gland; this causes the body to retain water.
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