A Better Marker for DKA
The nitroprusside test typically performed with a Bayer Acetest tablet is a laboratory classic. It’s one of the first tests I learned. In the nitroprusside reaction, acetoacetic acid, a serum or urine ketone, reacts with sodium nitroferricyanide and glycine to produce a purple color. I’ve been in labs where two-fold serial dilutions are common. Sample is dropped on the tablet, and you either see a color or not.
Acetone and beta-hydroxybutyrate (BOHB) are the other significant circulating ketone bodies during ketogenesis, a process that breaks down fat when there aren’t carbohydrates to burn for energy. This can happen while we sleep, fast, and in diabetics when there is a severe drop in insulin levels. Since ketones are acidic, the result is a measurable acidosis.
The problem with the nitroprusside test is simple: it doesn’t detect beta-hydroxybutyrate. This is significant in diabetic ketoacidosis (DKA) where the ratio of BOHB to acetoacetate may increase tenfold. BOHB has greater sensitivity and specificity in patients presenting to the ED with hyperglycemia and correlates better with treatment monitoring than anion gap or pCO2.
About two-thirds of patients with DKA have type 1 diabetes and can present to an ED with hyperglycemia, metabolic acidosis, electrolyte imbalance, dehydration, and or shock. From 1985 to 2005 DKA-related hospitalizations increased 42%, according to one source, suggesting this is an emerging problem that likely mirrors our obesity epidemic.
Clearly beta-hydroxybutyrate is a better marker for diagnosis and treatment of diabetic ketoacidosis. There are other applications such as alcoholic ketoacidosis, but in an emergent setting we’re more likely to encounter the former. Since the test needs to be performed STAT, it should be done point of care or in house.
I don’t know how many labs perform the test. I’ve been looking for opportunities to bring this test in house, and recently decided to evaluate a user-defined method for our Siemens analyzer. Our ED director is excited about this test, which is good. But in previous years there was less interest. It’s funny how these things depend on timing, an odd phenomena of laboratory business. It also keeps our job interesting.
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