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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