Tuesday, August 15, 2017

Osmolal gap

PulmCrit- August 14, 2017 - By Josh Farkas
..."This raises the question: What is the performance of the serum osmolal gap? Is this an evidence-based test for intoxicated patients?
  • There is disagreement regarding the best formula to calculate the osmolal gap, and what the appropriate cutoff value should be.
  • Most patients with an elevated osmolal gap don’t have toxic alcohol poisoning. Osmolal gap may be increased by numerous factors including renal failure, ketoacidosis, shock, electrolyte abnormalities, and contrast dye.
  • Performance of the osmolal gap to detect toxic alcohols varies widely depending on the equation used and laboratory techniques. A recent study suggests that it might have a positive likelihood ratio of ~1.2-1.7 and a negative likelihood ratio of ~0.3-0.45.
  • These performance characteristics are inadequate for broad clinical use, with the potential for frequent false-positive and false-negative results.
  • The use of osmolal gap as a diagnostic test for toxic alcohols is poorly supported by available evidence. If a new test were developed with this level of evidentiary support, there is no way it would gain FDA approval."