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Stool osmotic gap is a measurement of the difference in solute types between serum and feces, used to distinguish among different causes of diarrhea. Feces is normally in osmotic equilibrium with blood serum, which the human body maintains between 290–300 mOsm/kg. [ 1 ]
Urine osmolality in humans can range from approximately 50 to 1200 mOsm/kg, depending on whether the person has recently drunk a large quantity of water (the lower number) or has gone without water for a long time (the higher number). [2] Plasma osmolality with typical fluid intake often averages approximately 290 mOsm/kg H 2 O in humans. [2]
The osmol gap is typically calculated with the following formula (all values in mmol/L): = = ([+] + [] + []) In non-SI laboratory units: Calculated osmolality = 2 x [Na mmol/L] + [glucose mg/dL] / 18 + [BUN mg/dL] / 2.8 + [ethanol/3.7] [3] (note: the values 18 and 2.8 convert mg/dL into mmol/L; the molecular weight of ethanol is 46, but empiric data shows that it does not act as an ideal ...
Reference ranges for urine tests are described below: Measurement Lower limit Upper limit ... per High Power Field (HPF) RBC casts: n/a 0 / negative [2] White blood ...
A fluid or water deprivation test is a medical test [1] which can be used to determine whether the patient has diabetes insipidus as opposed to other causes of polydipsia (a condition of excessive thirst that causes an excessive intake of water). The patient is required, for a prolonged period, to forgo intake of water completely, to determine ...
In primary polydipsia, the urine osmolality should increase and stabilize at above 280 mOsm/kg with fluid restriction, while a stabilization at a lower level indicates diabetes insipidus. [18] Stabilization in this test means, more specifically, when the increase in urine osmolality is less than 30 Osm/kg per hour for at least three hours. [18]
Diagnosis is based on clinical and laboratory findings of low serum osmolality and low serum sodium. [13] Urinalysis reveals a highly concentrated urine with a high fractional excretion of sodium (high sodium urine content compared to the serum sodium). [14] A suspected diagnosis is based on a serum sodium under 138.
Usually the most important unmeasured ion in urine is NH 4 + since it is the most important form of acid excretion by the kidney. [5] Urine NH 4 + is difficult to measure directly, but its excretion is usually accompanied by the anion chloride. A negative urine anion gap can be used as evidence of increased NH 4 + excretion. In a metabolic ...