Page 37 - Clinical Biochemistry 08PB804

• Very low amounts of bilirubin can be detected in the urine, even when serum levels are
below the clinical detection of jaundice.
• False positive: metabolites of drugs: Phenazopyridin.
• False negative: Ascorbic acid, light sensitive.
3- Urobilinogen
• Urine urobilinogen is increased in any condition that causes an increase in production or
retention of bilirubin.
• It is increased in haemolytic anemia and liver disease, but negative in obstructive
juandice.
• False positive: Indol porphobilinogen.
• False negative: easily oxidized to urobilin.
4- Ketones
• Ketone bodies can be detected in diabetes mellitus, insulin deficiency or starvation,
prolonged vomiting, dehydration fever.
• It can be present in large amounts in the urine before any elevation in plasma levels.
• False positive: levodopa.
• False negative: Ascorbic acid, Ketone bodies are volatile.
5- Blood
• The presence of large numbers of RBCs in the urine sediment establishes the diagnosis of
hematuria. It can be detected in renal disease, trauma, renal stones, infection, heamolytic
anemia.
• False positive: Bacterial enzymes.
• False negative: ascorbic acid, high specific gravity (proteinuria).