D-lactate vs L-lactate

I’m on the CCU right now, and there’s a lot of learning to be had. To be honest, t

he learning curve for me having not done inpatient medicine at my institution is a little steep for the practical things like, admissions criteria, and how t

o make Epic work optimally for me. But on rounds

one day we were talking about D vs. L-lactate and I remember learning the difference, and then…forgetting it. So a brief review:

L-lactate vs D-lactate, all the lactates! 
Lactate = two isomers. L-lactate is what most lab measures. It’s what’s made from pyruvate during anaerobic metabolism (AKA tissue hypoperfusion).
D-lactate is also present in our bodies usually much less. It’s made by bacteria.
Time D-lactate is relevant:
Short Bowel Syndrome! (Or sometimes people with small intestine [SI] surgeries, or GI malabsorption) – Pretty rare syndrome.
Basically normally your SI breaks down carbs, but you can either get bacterial overgrowth into your SI after SI surgeries, or increased delivery of carbs to the colon. Either way, increased bacteria there = increased D-lactate production = D-lactate not broken down in the same way as L-lactate (by L-lactate dehydrogenase) so it’s reabsorbed = actually relevant lactic acidosis. These people usually present with a gap acidosis and altered mental status.
Illness script:  So if you see the combo of short bowel + gap metabolic acidosis after a high carb meal + altered mental status but a normal lactate, consider sending a D-lactate specifically, and it may be elevated!
**It’s also notable if they drink/get a bunch of propylene glycol because D-lactate is a metabolite of propylene glycol metabolism. You can find this in a lorazepam or diazepam infusion, but you generally need a lot of it to be relevant.

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