"Critical Care A Day"
Thursday January 21, 2026
Thursday January 21, 2026
Q: While calculating Effective Plasma Osmolality, particularly in hyperosmotic hyperglycemic nonketotic state (HHNK), which of the sodium (Na) concentrations should be used? - select one
A) Actual measured plasma Na concentration
B) Corrected Na concentration
Answer: A
The formula for effective Plasma osmolality (Posm) is a useful method for diagnosing HHNK, where effective Posm is typically >320 mOsm/kg.
The formula is:
Effective Posm = [2 x Na (mEq/L)] + [glucose (mg/dL) ÷ 18]
The Na concentration used should be the actual measured plasma Na concentration, not the corrected Na concentration with high glucose.
#endocrinology
#electrolytes
#metabolism
References:
1. Rasouli M. Basic concepts and practical equations on osmolality: Biochemical approach. Clin Biochem. 2016 Aug;49(12):936-41. doi: 10.1016/j.clinbiochem.2016.06.001. Epub 2016 Jun 22. PMID: 27343561.
2. Fazekas AS, Funk GC, Klobassa DS, Rüther H, Ziegler I, Zander R, Semmelrock HJ. Evaluation of 36 formulas for calculating plasma osmolality. Intensive Care Med. 2013 Feb;39(2):302-8. doi: 10.1007/s00134-012-2691-0. Epub 2012 Oct 19. PMID: 23081685.
A) Actual measured plasma Na concentration
B) Corrected Na concentration
Answer: A
The formula for effective Plasma osmolality (Posm) is a useful method for diagnosing HHNK, where effective Posm is typically >320 mOsm/kg.
The formula is:
Effective Posm = [2 x Na (mEq/L)] + [glucose (mg/dL) ÷ 18]
The Na concentration used should be the actual measured plasma Na concentration, not the corrected Na concentration with high glucose.
#endocrinology
#electrolytes
#metabolism
References:
1. Rasouli M. Basic concepts and practical equations on osmolality: Biochemical approach. Clin Biochem. 2016 Aug;49(12):936-41. doi: 10.1016/j.clinbiochem.2016.06.001. Epub 2016 Jun 22. PMID: 27343561.
2. Fazekas AS, Funk GC, Klobassa DS, Rüther H, Ziegler I, Zander R, Semmelrock HJ. Evaluation of 36 formulas for calculating plasma osmolality. Intensive Care Med. 2013 Feb;39(2):302-8. doi: 10.1007/s00134-012-2691-0. Epub 2012 Oct 19. PMID: 23081685.