chemical urine examination

reagent strips

-used for POC testing

-color change qualitative or semi-quantitative

4.8-7.5

urine pH range

inc

pH inc/dec after sitting out

ammonia

inc of this analyte inc pH of urine sitting out at RT

none

substances that interfere with pH

double indicator

system for pH measurement based on color change from orange (acid) to blue (alkaline)

protein

presence in urine indicative of:

-early renal disease

-nephrotic syndrome

-cold exposure, high fever, exercise, acute illness, pregnancy (pre-E)

-glomerular damage (SLE)

-strip: tetra bromophenol blue at pH 3

-false pos only

tetra bromophenol blue

indicator at pH 3 used for protein test on reagent strip

3

buffer pH for protein reagent strip test

pos

protein results are pos/neg with:

-blood

-casts

-WBCs

-bacteria

protein

reagent strip test that has no false negatives

pos

false pos/neg results for protein reagent strip test with:

-alkaline urine (buffer interference)

-run-over

-x-ray dyes

-drugs

Bence Jones proteins

monoclonal Ig light chains

-multiple myeloma patients

-precipitate at 40-60 C → dissolve at 100 C

100 C

T that Bence Jones proteins precipitate at but normal proteins don;t

<10, <150

normal protein in urine mg/dL and mg/24 hr

Tamm-Horsfall

protein that makes casts

orthostatic proteinuria

proteins present in urine after standing but not in morning (after lying down)

glucose

-presence indicates DM or tubular reabsorption issues

-strip: glucose oxidase, peroxidase, chromogen, buffer

-false neg and false pos

glucose oxidase, peroxidase, chromogen, buffer

reagents in glucose reagent strip test

pos

false pos/neg for glucosuria with:

-peroxide or oxidizing substance contamination

neg

false pos/neg glucosuria with:

-ascorbic acid

-5-HIAA

-homogentisic acid

-aspirin

-leodopa

160-180

renal glucose threshold (mg/dL)

ketones

intermediates of fat metab

-DM monitoring

-vom

-starvation

-weight reduction

-reagents: Na nitroprusside (dipstick or acetest tablets)

-false pos and neg

Na nitroprusside

reagent in ketone reagent strip test

purple

color of ketone test

acetone, acetoacetic acid, B-hydroxybutyric acid

ketones

dipstick

-ketone detection test

-acetoacetic acid reacts with Na nitroprusside

acetest tablet

-ketone detection test

-acetoacetic acid and acetic acid react with Na nitroprusside

pos

false pos/neg for ketones:

-highly pigmented urine

-levodopa metabolites

-sulfhydryl compounds

neg

false pos/neg for ketones:

-bacterial breakdown after sitting out for too long

hematuria

-RBCs in urine

-renal issue, renal caliculi (passing), glomerulonephritis, tumors, trauma, pyelonephritis, toxic chemical exposure

-cloudy pink

-confirm with microscope

-pos RBC test

hemoglobinuria

-Hgb presence in urine

-red

-due to intravascular hemolysis (pre-renal)

-pos RBC test

myoglobinuria

-clear

-protein from muscle breakdown

-muscle wasting disease, trauma, prolonged coma, convulsions, excessive exercise

-pos RBC test

RBCs

-hematuria, hemoglobinuria, myoglobinuria

-reagent: hydrogen peroxide, tetramethyl-benzidine, buffer

-detects intact and lysed RBCs

-false pos and neg

hgb

in RBCs, has pseudoperoxidase activity, reacts with tetramethyl-benzidine and hydrogen peroxide

hydrogen peroxide, tetramethyl-benzidine, buffer

reagents in RBC test strip

neg

false pos/neg RBC test with:

-nitrite inc (bacteria)

-protein

-ascorbic acid

-low pH

-elevated SG

pos

false neg/pos RBC test with:

-menstrual contam

-strong oxidizing detergents

-bacterial presence

bilirubin

-hgb breakdown metabolite

-liver issues, bile obstruction

-conjugated in urine

-reagents: diazonium salt 

-purple

-false pos and neg

diazonium salt

reagent in bilirubin test strip

neg

false pos/neg bilirubin with light exposure

pos

false pos/neg wtih dark yellow urine pigment

urobilinogen

-liver disease, hemolytic disorders

-reagents: p-dimethylaminobenzaldehyde

-red color

-not present in biliary obstruction

-false pos and neg

p-dimethylaminobenzaldehyde

reagent for urobilinogen test

pos

false pos/neg for urobilinogen test with:

-salicylates

-pyridine

-sulfonamides

neg

false pos/neg urobilinogen test with:

-formalin

-high nitrites

-light exposure

nitrite

-UTI screen (most commonly E. coli) → bacteria

-cystitis

-Greiss rxn

-reagents: acid pH, p-arsanilic acid, diazo compound, quinoline

-pink

-most accurate pos after morning void (sat in bladder long enough for metabolism)

-false pos and neg

p-arsanilic acid, diazo cmpd, quinoline

reagents in Greiss rxn for nitrite strip test

acidic

pH for nitrite test is acidic/alkaline

pos

false pos/neg for nitrite test when sample not tested quickly enough

neg

false pos/neg for nitrite test with:

-high SG

-ascorbic acid

-high urobilinogen

SG

-ability of kidneys to dilute/concentrate urine

-change in pKa of polyelectrolyte

-indicator: bromothymol blue

bromothymol blue

indicator dye for SG on strip test

1.003-1.035

normal SG

leukocyte esterase (WBC)

-UTI

-not quantitative

-reagents: esters and diazo salt

-rxn: WBC granule esterases react with reagent and produce purple cmpd

-false pos and neg

esters, diazo salt

reagents for leukocyte esterase strip test

pos

false pos/neg for WBCs with:

-strong oxidizing agents

-formalin

-vag fluid

-eos

-trichomonas

neg

false pos/neg test for WBCs with:

-high SG

-ascorbic acid

-antibiotics

-high [protein]

-high [glucose]