Trace urine acetone.
A According to the manufacturer of Acetest Reagent Tablets (Bayer Corp.), results are recorded as negative if no purple color is apparent on the tablet at the appropriate reading time. Any pink, tan, or yellow color should be disregarded. Positive results are recorded as small, moderate, or large on comparison with the color chart provided.
In terms of specific performance characteristics, the small color block corresponds to approximately 20 mg acetoacetic acid/dL, moderate to 30 mg/dL to 40 mg/dL, and large to approximately 80 mg/dL to 100 mg/dL. The minimum detectable level, however, is stated to be as little as 5 mg of acetoacetic acid/dL in urine.
Therefore, if the presence of a slight but definite purple color that appeared less than the "small color block" was reported as negative, the presence of acetoacetic acid at detectable levels would be unreported. It seems reasonable that such findings be reported as "trace." This is done with the reagent strips for ketones. Reagent strips for ketones (Multistix/Ketostix) utilize color blocks corresponding to trace/5 mg/dL, small/15 mg/dL, moderate/40 mg/dL, and large/80 mg/dL to 160 mg/dL acetoacetic acid.
Low levels of ketones are difficult to read with reagent strips and tablet tests. The use of negative quality-control urine, which shows a complete lack of similar purple color, is very helpful in illustrating the difference between a negative and trace result.
According to product inserts, detectable ketone levels may occur in urine during physiological stress conditions such as fasting, pregnancy, and frequent strenuous exercise. Some urine specimens with high specific gravity and low urine pH may give reactions up to and including trace, and clinical judgment is needed to determine the significance of these results.
--Karen M. Ringsrud, MT(ASCP)
Department of Laboratory Medicine and Pathology, University of Minnesota Medical School
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|Title Annotation:||Answering your questions|
|Author:||Baer, Daniel M.|
|Publication:||Medical Laboratory Observer|
|Date:||Sep 1, 2006|
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