![]() ![]() ^ Ammar KA, Heckerling PS (January 1996)."Osmolality gaps: diagnostic accuracy and long-term variability". "Osmolality and osmolarity: narrowing the terminology gap". ^ Converting between osmolality and osmolarity."Serum osmolal gap in patients with idiopathic nephrotic syndrome and severe edema". ^ Kapur G, Valentini RP, Imam AA, Jain A, Mattoo TK (June 2007)."Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap". ^ Purssell RA, Pudek M, Brubacher J, Abu-Laban RB (December 2001)."An evaluation of the osmole gap as a screening test for toxic alcohol poisoning". ^ Lynd LD, Richardson KJ, Purssell RA, et al.^ "Osmolality Gap - Calculation and Interpretation".If, however, the calculated gap is above an acceptable range, then it is an indication that there is something else dissolved in the serum that is producing an osmol gap, which can be a major clue in determining what is ailing the patient. If this gap falls within an acceptable range,(<10) then it is assumed that sodium, glucose, BUN are indeed the major dissolved ions and molecules in the serum. The calculated osmolality is then subtracted from the measured osmolality to provide the osmol gap, or the difference between these two values. This measurement gives the true plasma osmolality. This vial is put in an instrument that measures the freezing point depression of all the solutes in the plasma. A second vial is also sent to the laboratory. From this measurement, the clinician can calculate the plasma osmolality of a patient's blood. As part of a laboratory blood test, a vial of blood is tested for the amount of these four ions and molecules that are present in the blood. The major constitutionals of clinical importance are sodium ions, glucose, and blood urea nitrogen (BUN), plus ethyl alcohol in a person who has been drinking. There are a variety of ions and molecules dissolved in the serum. Theory Pathophysiology sample values BMP/ ELECTROLYTES: propylene glycol toxicity (as with intravenous infusions where it is used as an excipient, e.g.Accordingly, intoxications as listed below are reasons for an increased osmolar gap. Ĭauses of an elevated osmol gap are numerous.Īll four are osmotically active substances found in humans. ![]() Osmol gaps are used as a screening tool to identify toxins. When this is not the case, the term "osmol gap" can be used when units are mixed to provide a clinical estimate. To avoid ambiguity, the terms "osmolal" and "osmolar" can be used when the units of molality or molarity are consistent throughout the calculation. Because the calculated osmol gap can therefore be a conflation of both terms (depending on how it is derived), neither term (osmolal gap nor osmolar gap) may be semantically correct. For this reason, the terms are often used interchangeably, though some object to equating the terms. This is because the difference in absolute value of these two measurements that can be attributed to the difference in units will be negligible in a clinical setting. While it is possible to convert between osmolality and osmolarity, thereby deriving a more mathematically correct osmol gap calculation, in actual clinical practice this is not done. When a measure of serum solutes is calculated, it is often done in units of osmolarity. Since laboratories measure serum solutes in terms of freezing point depression, the reported units are properly units of osmolality. (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 osmole in solution and the appropriate divisor is 3.7 )Ī normal osmol gap is < 10 mOsm/kg. (all values in mmol/L)Ĭalculated osmolality = 2 x + / 18 + / 2.8 + OG = measured serum osmolality − calculated osmolalityĬalculated osmolality = 2 x Na + Glucose + Urea. The osmol gap is typically calculated as: Osmol gap in medical science is the difference between measured serum osmolality and calculated serum osmolality. Potassium.Osmolal gap, osmolality gap, osmolar gap osmole gap Diabetes tests.Īmerican Association for Clinical Chemistry. doi: 10.1007/s4026-zĬenters for Disease Control and Prevention. Drug-Induced Hyperglycaemia and Diabetes. Blood glucose & A1C diagnosis.įathallah N, Slim R, Larif S, et al. doi:10.1002/4Īmerican Diabetes Association. Clinical laboratory tests - reference values. ![]() Abnormal basic metabolic panel findings: implications for nursing. ![]()
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