Urinalysis: Part 1 Flashcards
Types of Urine Specimens (with regards to timing)
Timing
Random
–Collected without regard to time
First morning (void) ----Most concentrated
24-hour or timed
Types of Urine Specimens with regards to source/collection
Source/collection
Catheterized
-Tube inserted into bladder via urethra
Midstream clean-catch
-Best for urine cultures
-Clean external meatus (urethral opening)
-Discard initial void, then collect sample
Suprapubic – percutaneous syringe aspirate -directly from bladder
Pediatric
-U-Bag
-Adhesive attachment around perineum
Is urine a biohazard? Collection and Handling
Biohazard substance?
— use standard precautions
Container: clean, dry, leak-proof, wide-mouth, plastic
Minimum 10-12 ml (manual procedures)
—-Must be standardized w/in institution
Tested within 2 hours, otherwise refrigerate
—–Loss of formed elements and cells
Chemical preservatives available, must check test requirements first (esp. dip and culture)
What changes/factors are we looking at in unpreserved urine?
Color – darkens or changes (esp. bilirubin/urobilinogen)
Clarity – decreases (xtal, ppt formation, bacterial growth)
RBCs and WBCs lyse (alkaline or dilute)
Casts dissolve (alkaline or dilute)
Bacteria – increase by exponential growth
pH – increase (urea hydrolyzed to NH3 by bacteria)
Glucose – decrease (bacteria, yeast, cell consumption)
Ketones – decrease (acetone evaporation, AcOAc brkdn)
Bilirubin and urobilinogen - decrease
—Oxidative and photo-decomposition
Nitrite – increase (bacterial conversion of nitrates)
Describe the physical Examination of Urine
Evaluate using well-mixed urine, through a clear container, against white background with adequate room lighting:
Color Clarity Odor Concentration by Specific Gravity Volume
What color is normal urine?
yellow urochrome
Colorless, straw, or pale yellow urine can be a result of what?
recent fluid consumption, polyuria or diabetes insipidus, diabetes mellitus
Dark yellow, amber or orange urine can be a result of what?
concentrated specimen, ingestion of carrots or vitamin A, presence of pyridium or bilirubin
Yellow-green, yellow-brown urine can be a result of what?
Bilirubin oxidized to biliverdin
Pink/ red urine is a result of what?
RBCs, hemoglobin, myoglobin , porphyrins, beets, menstrual contamination
Brown or black urine can be caused by what?
RBCs, Hgb oxidized to metHgb, myoglobin, homogentisic acid (alkaptonuria), melanin
How would someone have purple urine?!
Purple discoloration can occur in alkaline urine as a result of the degradation of indoxyl sulfate (indican), a metabolite of dietary tryptophan, into indigo (which is blue) and indirubin (which is red) by bacteria such asProvidencia stuartii, Klebsiella pneumoniae, P. aeruginosa, Escherichia coli,and enterococcus species.
Urine clarity: normal vs pathologic
Normal urine should be clear
Hazy, cloudy, turbid and milky due to
pathologic or nonpathologic causes:
—-Crystals, precipitate or calculi (stones)
—-RBCs, WBCs (pyuria), bacteria, yeast, sperm, fat
—-Prostatic fluid, mucous threads
—-X-ray media, fecal contamination
—-Chyluria – lymph (chyle) in urine
Urine odors? Normal vs ….not normal
Normal: faintly aromatic
Ammoniacal/foul: may indicate presence of bacteria due to UTI, improper storage
Sweet, fruity: may indicate presence of ketone bodies due to diabetes mellitus, starvation, strenuous exercise, vomiting, diarrhea, malnutrition
Maple syrup: maple syrup urine disease
Genetic defect in Leu, Ile, Val (BCAAs) metabolism
Physical Exam. of Urine: Concentration
How is concentration expressed?
What is specific gravity?
How is specific gravity measured?
Function of solutes present and volume excreted
Expressed as specific gravity or osmolality
Specific gravity: ratio of the density of urine to the density of an equal volume of pure water
SG measured directly or indirectly
- —Indirect: refractometer, reagent strip
- —–Direct: urinometer (rarely used)
Specific Gravity: Ranges?
Low SG?
High SG?
Ranges: 1.002-1.040
- Kidney cannot concentrate >1.040
- ——–Renal medulla max. SG ~1.040
- Most commonly 1.010-1.025 (glom. filtrate ~1.010)
Low SG (hyposthenuric):
- diabetes insipidus
- renal tubular disease - kidney cannot concentrate urine
High SG (hypersthenuric):
- DM
- fever, vomiting, diarrhea (causing dehydration)
- radiographic dyes, mannitol (esp. if >1.040)
Physical Examination of Urine: Volume
Normal vs not normal?
Normal: 600-2000 mL/day
Polyuria: >2 L/day: excessive liquid intake, diabetes mellitus or insipidus
Oliguria:
What tests are read from a urine dipstick? (chemical analysis)
Leukocyte Esterase Nitrite Urobilinogen Protein pH Blood Specific Gravity Ketones Bilirubin Glucose
Chemical principle behind Urine Dipstick: Glucose?
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Uses and Limitations of Urine Glucose Detection?
Significance (increases only)
- –Diabetes mellitus
- –Renal glycosuria – lowered renal threshold
- ——-Renal disease
- ———-Pregnancy (5-10% of cases)
Limitations
- –Interference: reducing agents (esp. vitamin C)
- ———-False negative or decrease
- –Only measures glucose and not other sugars.
- –Renal threshold (normally 160-180 mg/dL) must be passed in order for glucose to appear in the urine.
Other Tests
CuSO4 test for other reducing sugars (Clinitest, Benedict’s test).
—Galactose, fructose, xylose, maltose, lactose
—Not sucrose
Describe the detection of Reducing Sugars by CuSO4.
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Urine Dipstick: Bilirubin
Describe the chemical principle behind this test.
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Uses and Limitations of Urine Bilirubin Detection
Significance Increased direct bilirubin in plasma Indirect is bound to albumin and normally not filtered Elevated in most liver disease except ----Pre-hepatic jaundice ----Gilberts syndrome -----Crigler-Najjar syndromes
Limitations
Decreased by prolonged exposure of sample to light
False positives with red-colored drugs in urine
Confirm positives with Ictotest tablet
Serum test for total and direct bilirubin is more informative
Other Tests
Serum total and direct bilirubin
What is the Ictotest?
- More sensitive (4x) tablet version of dipstick assay
- Especially useful to confirm dipstick in highly colored urines
- 10 drops urine applied to reagent pad
- Ictotest tablet placed upon pad
- 2 drops water added to tablet
- After 30 seconds, evaluate visually
- Purple or blue color is positive
The Urine Dipstick: Urobilinogen
Chemical Principle?
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Uses and Limitations of Urobilinogen Detection
Significance
Increased: increased hepatic processing of bilirubin
Decreased: biliary obstruction (with positive bilirubin)
—–Urine urobilinogen levels are normally low
Limitations
Decreased: prolonged exposure of specimen to oxygen and light (urobilinogen —> urobilin)
Multi-Stix also positive for porphobilinogen, 5-HIAA, some drugs
ChemStrip specific for urobilinogen
Other Tests
Serum total and direct bilirubin
Bilirubin negative, urobilinogen increased?
Prehepatic:
Increased heme degradation, hemolytic conditions, transfusion reaction, sickle cell disease
Ineffective erythropoiesis due to thalassemia or pernicious anemia
Bilirubin positive, urobilinogen incr. or normal?
Hepatic:
hepatitis, cirrhosis, genetic defects
Bilirubin positive, urobilinogen absent or low?
Posthepatic: obstruction, carcinoma, calculi, fibrosis
The Urine Dipstick: Ketones
Chemical Principle?
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Uses and Limitations of Urine Ketone Detection?
Significance
Diabetic ketoacidosis
Prolonged fasting, starvation, carbohydrate loss
Limitations
False positive with sulfhydryl drugs (e.g., captopril)
Only measures acetoacetate (may partially measure acetone) while BHB is the major “ketone”
Other Tests
Ketostix (more sensitive tablet version of same assay)
Acetest tablet test (urine, serum/plasma, whole blood)
Serum glucose and electrolytes to confirm DKA
Serum ß-hydroxybutyrate
The Urine Dipstick: Specific Gravity
Chemical Principle?
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Uses and Limitations of Urine Specific Gravity
Significance
Diabetes insipidus
Dehydration
Limitations
Reported in 0.005 increments only
Alkaline (>6.5) urine reads ~0.005 too low
Does not measure non-ionized solutes (e.g. glucose, urea)
More “accurately” assesses SG (urine concentrating ability) when non-ionic solutes present
Other Methods
Refractometry
—Hydrometer (urinometer) DO measure non-ionized solutes
—-Osmolality measurement DO measure non-ionized solutes
Urine Dipstick: Blood
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