Our fellowship director asked me to do a lecture on osmolar gap. At first I thought that this was an odd topic as toxic alcohols, the standard reason for determining an osmolar gap are relatively rare findings and I was worried I’d be able to find enough to talk about for an hour.
I’m really happy how the lecture turned out. Not my best but pretty strong for a first crack at a new topic.
I structured the topic by looking at patients with low, normal and high anion gaps to go along with the high osmolar gap and started with a case of a high osmolar gap paired with a negative anion gap. I have only seen one negative anion gap and that was a case of hyperkalemia and hypoalbuminemia. This case comes from the Canadian Medical Association Journal. The low anion gap is from the unmeasured cation, lithium. The patient had a lithium level of 14.5 mmol/L.
Lithium is an unmeasured cation which expands the red box and decreases the anion gap.
The differential for a decreased anion gap.
The osmolar gap is driven up because the cation lithium is not part of the calculated osmolality but contributes to the measured osmolality. A unifying theme of osmolar gap is that adulterants that increase the osmolar gap always have relatively low molecular weights. Lithium carbonate does not disappoint with a molecular weight of only 74. Other intoxicants associated with an increased osmolar gap, likewise have a low molecular weight.
The case report then deals with the dialytic removal of lithium and the nature of lithium toxicity.
Here are the causes of an osmolar gap divided by anion gap:
Here it is:
Osmolar Gap
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my anion gap is 2, my potassium is 4.3…… what is going on?
That is a low anion gap. This should be addressed by the doctor that ordered the lab. A list of diagnosis associated with a low anion gap are included in the post. Hope all goes well.
Hello!
my anion gap went from 8 to a 2 since last year.(normal range 4-20) Sounds bad to me… Is is because my Potassium level went up to 5.4 from a 4.3? Creatinine also lowered to 0.7
and urine blood showed up 2+ that's new to me.
I am 61 years old, caucasian female.
All this is scaring me, doctor sent me back for a retake on the urinalysis. No news yet.
A repeat on the rrinqlysis is the right thing to do. FRegarding the low anion gap, the increased potassium will explain only part of the change. Fishing for the cause of an abnormally low anion gap in the absense of any other symptoms is likely to lead to lots of tests and no definitive diagnosis.
Good luck and make sure you follow your doctor's advice on what work-up she requests.
Joel
I have a low anion gap of 5. eos% is high 7.3
eos# is high .6. All other bloodwork is in
normal range. pottasium is 4.2 albumin 4.3
I am a 59 year old caucasian female, who has been experiencing extreme nausea, and weight loss with fatigue and muscle weakness. My blood work came back with a potassium level at 5.5 and a anion gap of 6. Much of what I have come up with, searching the net is possible Addisons Disease. I will be following up with my P.A at Henry Ford Health Systems, Hall Road, but really do not know what type of specialist deals with possible disorders associated with the blood.
Hi! I am a 44 year old woman with an anion gap of 3 and a potassium level of 5.4. Do I need to get this checked out? What could it mean, if anything? Thanks!