Sugars that can react as reducing substances:
(1) glucose
(2) lactose
(3) fructose
(4) galactose
(5) pentose sugars
Glucose in the urine may reflect diabetes mellitus or a disorder of the proximal renal tubule.
Sucrose will not be detected as a reducing substance
Drugs and chemicals (may require large doses):
(1) salicylates
(2) penicillin
(3) ascorbic acid
(4) nalidixic acid
(5) cephalosporins
(6) probenecid
(7) sulfonamides
(8) metabolites of methapyrilene (antihistamine)
(9) cysteine or other amino acids (may occur in patients receiving TPN)
(10) chloral hydrate
(11) chloramphenicol
(12) hippurate
(13) creatine
(14) oxalate
(15) glucuronates
(16) homogentisic acid (alkaptonuria)
(17) isoniazid
(18) nitrofurantoin
(19) streptomycin
(20) tetracyclines
(21) uric acid
where:
• Henry et al say that ketone bodies are not reducing substances while Siberry and Iannone say they are.
Workup:
(1) The most common reducing substance is in the urine is glucose. A specific method for glucose (glucose oxidase, other enzyme, dipstick) will be positive. A test for reducing substances is done on children with a negative dipstick.
(2) If an inborn error of sugar metabolism is suspected, then chromatography is performed to determine the type, which can then be quantitated.
(3) If a drug is suspected, then either
(3a) the concentration of the drug in the urine can be measured, or
(3b) the drug can be discontinued which should be followed by a negative test for reducing substances
(4) Examine the urine sediment for crystals (oxalate, urates, cysteine, sulfonamides, other).
(5) If an inborn error of amino acid metabolism is suspected, measure urinary excretion of amino acids.
