Chemical Examination of Urine

Question 1

pH

Answer 1

Normal is 4.5-8 (morning is 5-6)

Strip uses methyl red and bromthymol blue to detect pH

Question 2

Protein

Answer 2

Uses tetrabromphenol blue to detect protein
False neg = proteins other than albumin, too dilute
False pos = pH > 9, strip in urine too long

Question 3

Creatinine

Answer 3

Creatinine in urine complexes with copper in strip, catalyzes oxidation of chromagen to colored product
False neg = ascorbic acid

Question 4

Glucose

Answer 4

Glucose reacts to form peroxide which forms oxidized chromagen colored product
False pos = oxidizing agents (bleach)
False neg = ascorbic acid, alkaline pH, high specific gravity

Question 5

Ketones

Answer 5

Strip has sodium nitroprusside and glycine to measure all intermediates
False pos = dyes/pigments, phenylketones
False neg = Bacteria, ketones released when container opened

Question 6

Blood

Answer 6

Detects pseudoperoxidase activity of hemoglobin and myoglobin to form oxidized chromagen colored product (tetramethylbenzidine)
False pos = vegetable peroxidase, E. coli
False neg = ascorbic acid, nitrits, formalin

Question 7

Bilirubin

Answer 7

Diazonium salt to form colored azobilirubin
False pos = pigments
False neg = Old specimen, exposed to light, ascorbic acid, nitrite

Question 8

Urobilinogen

Answer 8

Uses Ehrlich’s reagent or diazo dye to detect urobilinogen
False pos = pigments
False neg = Improper storage, nitrites

Question 9

Nitrites

Answer 9

Tests for UTI’s, detects ability of bacteria to reduct nitrate to nitrite by reacting nitrite with aromatic amine to form colored product
False pos = old urine, bacterial contamination, pigments
False neg = ascorbic acid, antibiotics, bacteria that reduce nitrate all the way to nitrogen (skip nitrite)

Question 10

Leukocytes

Answer 10

UTI or inflammation
Leukocyte esterase reacts with acid ester to form colored compound
False pos = pigments, oxidizing agents
False neg = glucose, protein, ascorbic acid, pigments, high specific gravity, lymphocytes, antibiotics