Tyrosine-derived 4-hydroxyphenylpyruvate reacts with ketone  test fields of 3 commercially available urine dipsticks.
BACKGROUND
The enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) is key in tyrosine catabolism. Inhibition of HPPD results in tyrosinemia and increased urinary excretion of 3 phenylketones: 4-hydroxyphenylpyruvate (HPPA), 4-hydroxyphenyllactate (HPLA), and 4-hydroxyphenylacetate (HPAA). A previous study involving administration of a novel HPPD inhibitor to dogs resulted in detection of ketonuria in treated animals using urine dipsticks read by reflectance photometry. Dipstick-positive results were suspected to be false because high concentrations of urinary phenylketones have been reported to react with ketone test fields of urine dipsticks, but visual confirmation was not performed.


OBJECTIVE
The purpose of this study was to determine which of the 4- hydroxyphenolic acids produced by HPPD inhibition react with ketone test fields of 3 commercially available urine dipsticks.


METHODS
Canine urine samples were prepared with HPPA, HPLA, HPAA, and lithium acetoacetate (positive control) at 6 concentrations. Unmodified urine samples were used as negative controls. All samples were tested for ketones using Combur 10 Test M dipsticks read by a Miditron dipstick analyzer. Urinalysis was also performed by visually inspecting ketone test fields on the Combur 10 Test M, Multistix 10 SG, and Aution 10 EA dipsticks.


RESULTS
Urine samples containing HPPA were positive for ketones with Combur 10 Test M dipsticks read by the Miditron analyzer and produced a red–brown color change in ketone test fields of all 3 dipsticks. Urine samples containing HPLA and HPAA were negative by all methods.


CONCLUSIONS
The phenylketone HPPA reacts with ketone test fields of 3 commercially available urine dipsticks, producing a red–brown color change that may be misinterpreted as positive for ketones by reflectance photometry.
Cartwright
James
J
Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire, RG42 6EY, UK. cartwrij@ukorg.huntingdon.com
Green
Richard M
RM
D000818:Animals; D004283:Dog Diseases / Q000175:diagnosis / Q000378:metabolism / Q000652:urine; D004285:Dogs / Q000378:metabolism / Q000652:urine*; D005189:False Positive Reactions; D005260:Female; D007659:Ketones / Q000652:urine*; D007662:Ketosis / Q000175:diagnosis / Q000378:metabolism / Q000652:urine; D008297:Male; D010648:Phenylacetates / Q000378:metabolism / Q000652:urine; D010666:Phenylpropionates / Q000378:metabolism / Q000652:urine; D010667:Phenylpyruvic Acids / Q000378:metabolism* / Q000652:urine; D011933:Reagent Kits, Diagnostic / Q000592:standards / Q000662:veterinary; D011934:Reagent Strips; D014443:Tyrosine / Q000378:metabolism* / Q000652:urine
D007659:Ketones; D010648:Phenylacetates; D010666:Phenylpropionates; D010667:Phenylpyruvic Acids; D011933:Reagent Kits, Diagnostic; D011934:Reagent Strips; C010590:4-hydroxyphenylpyruvic acid; C001418:4-hydroxyphenyllactic acid; C026246:4-hydroxyphenylacetate; D014443:Tyrosine