The release of free fatty acids associated with lipolysis results in an increased production of ketone bodies with increased levels of acetoacetic acid, acetone and beta-hydroxybutyric acid (BHBA).
Methods for measuring ketone bodies:
(1) nitroprusside-based (Acetest, Ketostix): This method primarily detects acetoacetic acid. It reacts to a lesser degree with acetone and does not react with BHBA.
(2) beta-hydoxybutyric acid (BHBA) quantification using BHBA dehydrogenase
Testing with a nitroprusside-based method without measurement of BHBA can result in a false negative diagnosis for ketoacidosis if BHBA is present in large amounts and if acetoacetate is absent or present in small amounts.
Causes of false negative nitroprusside test may include:
(1) highly acidic urine
(2) use of expired reagents
(3) deterioration of reagent (humidity, other)
(4) prolonged storage of urine specimen at room temperature
(5) abnormal urine color sufficient to interfere with readability
(6) failure to follow the testing procedure
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