We use the formula (1.86Na + glucose + urea +9)/0.93 to screen for non-ethanol volatiles in specimens from Emergency. Osmolar gaps over 15 (after accounting for the measured ethanol) are referred out alcohol testing by GC. This was determined empirically and seems to have worked for many years now. The 0.93 accounts for the % water phase in serum. This is discussed in the textbook Toxicologic Emergencies by Lewis Goldfrank et al 5th ed 1994. The calculation can be performed on the analyzer or a LIS.
Mario D'Costa Ph.D. FCACB
Director of Clinical Chemistry and Core Lab
St. Joseph's Health Centre
30 The Queensway, Toronto
On, Canada, M6R 1B5
Tel: 416-530-6263
Fax: 416-530-6559
email: [log in to unmask]
>>> <[log in to unmask]> 05/28/02 08:55AM >>>
A quick trawl of a few reference textbooks on my shelf gives a number of different versions for calculated osmolarity. Would anybody like to tell me which one (if any) is correct ?
(1) Zilva & Pannall 4th Ed:
2Na + urea + glucose ("approximate osmolarity")
(2) Walmsley & White 2nd Ed
2Na + urea + glucose (noting that NaCl does not completely ionize and 1.86 gives a more accurate estimation).
(3) Marshall WJ, 4th Ed
2Na + urea + glucose
(4) Clinical Biochemistry, Metabolic and Clinical Aspects:
1.89Na + 1.38K +1.03 urea + 1.08 glucose + 7.45
Chapter by M Penney; formula attributed to Clin Chem 1984; 30: 1703-1705
(5) Royal College of Pathologists of Australasia: Manual of Use and Interpretation of Pathology tests:
1.86 (Na + K) + glucose + urea + 10
Thanks
Chris Florkowski
Christchurch, NZ
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