serum osmolality

serum osmolality

Etymology: L, serum, whey; Gk, ōsmos, impulse

a measure of the osmotic concentration of blood serum, expressed as the number of osmoles of solute per kilogram of plasma water.

---

osmolality

the concentration of a solution in terms of osmoles of solutes per kilogram of solvent.

---

serum osmolality

a measure of the number of dissolved particles per unit of water in serum. In a solution, the fewer the particles of solute in proportion to the number of units of water (solvent), the less concentrated the solution. A low serum osmolality would be indicative of a higher than usual amount of water in relation to the amount of particles dissolved in it. It would be expected, then, that a low serum osmolality would accompany overhydration, or edema, and an increased serum osmolality would be present in a state of fluid volume deficit.

Measurement of the serum osmolality gives information about the hydration status within the cells because of the osmotic equilibrium that is constantly being maintained on either side of the cell membrane (homeostasis).

Water moves freely back and forth across the membrane in response to the osmotic pressure being exerted by the molecules of solute in the intracellular and extracellular fluids. Serum osmolality reflects the status of hydration of the intracellular as well as the extracellular compartments and thus describes total body hydration.

urine osmolality

a measure of the number of dissolved particles per unit of water in the urine. A more accurate measure of urine concentration than specific gravity, urine osmolality is useful in diagnosing renal disorders of urinary concentration and dilution and in assessing status of hydration.

---

serum

pl. sera, serums [L.] the clear portion of any animal or plant fluid that remains after the solid elements have been separated out. The term usually refers to blood serum, the clear, straw-colored, liquid portion of the plasma that does not contain fibrinogen or blood cells, and remains fluid after clotting of blood.

Blood serum from animals whose bodies have built up antibodies is called antiserum or immune serum. Inoculation with such an antiserum provides temporary, or passive, immunity against the disease.

---

serum albumin mastitis test

a high concentration of serum albumin in milk indicates the presence of mastitis in the quarter.

antilymphocyte serum

see antilymphocyte serum.

serum breaks

in classical swine fever (hog cholera) vaccination when a serum-simultaneous vaccination program is not effective and it is assumed that the hyperimmune serum was ineffective.

serum clot time

see prothrombin consumption test.

serum enzymes

enzymes of individual tissues are released into the blood when the tissue is damaged or when there is much activity in it. The levels are used as a measure of activity or injury.

serum-fast

resistant to the effects of serum.

serum glutamic-oxaloacetic transaminase (SGOT)

see aspartate aminotransferase.

serum glutamic-pyruvic transaminase (SGPT)

see alanine aminotransferase.

immune serum

serum from an immunized animal, containing specific antibody or antibodies.

serum osmolality

a measure of the number of dissolved particles per unit of water in serum. See also serum osmolality.

pooled serum

the mixed serum from a number of animals.

serum protein

see serum protein.

serum sickness

a group of immediate or antibody-mediated hypersensitivity reactions (also referred to as type III hypersensitivities) that includes Arthus reaction, serum sickness and immune complex diseases. The pathogenesis involves formation of bulky antibody-antigen complexes in the walls of small blood vessels; the complexes fix complement and cause necrosis and thrombus formation. There is infiltration of polymorphonuclear cells from which lysosomal enzymes are released.

serum-simultaneous immunization

an outdated method of vaccination, most popular at one time in the vaccination of pigs against classical swine fever (hog cholera). Live virus and antiserum to the virus were injected into the patient simultaneously; breakdowns in the system were frequent, leading to severe outbreaks of the target disease.

serum thymic factor

a humoral factor enhancing T lymphocyte responsiveness.