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Clinical Chemistry > Urinalysis: Part 1 > Flashcards

Urinalysis: Part 1 Flashcards

1
Q

Types of Urine Specimens (with regards to timing)

A

Timing

Random
–Collected without regard to time

First morning (void)
----Most concentrated

24-hour or timed

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2
Q

Types of Urine Specimens with regards to source/collection

A

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

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3
Q

Is urine a biohazard? Collection and Handling

A

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)

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4
Q

What changes/factors are we looking at in unpreserved urine?

A

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)

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5
Q

Describe the physical Examination of Urine

A

Evaluate using well-mixed urine, through a clear container, against white background with adequate room lighting:

Color
Clarity
Odor
Concentration by Specific Gravity
Volume
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6
Q

What color is normal urine?

A

yellow urochrome

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7
Q

Colorless, straw, or pale yellow urine can be a result of what?

A

recent fluid consumption, polyuria or diabetes insipidus, diabetes mellitus

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8
Q

Dark yellow, amber or orange urine can be a result of what?

A

concentrated specimen, ingestion of carrots or vitamin A, presence of pyridium or bilirubin

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9
Q

Yellow-green, yellow-brown urine can be a result of what?

A

Bilirubin oxidized to biliverdin

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10
Q

Pink/ red urine is a result of what?

A

RBCs, hemoglobin, myoglobin , porphyrins, beets, menstrual contamination

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11
Q

Brown or black urine can be caused by what?

A

RBCs, Hgb oxidized to metHgb, myoglobin, homogentisic acid (alkaptonuria), melanin

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12
Q

How would someone have purple urine?!

A

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.

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13
Q

Urine clarity: normal vs pathologic

A

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

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14
Q

Urine odors? Normal vs ….not normal

A

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

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15
Q

Physical Exam. of Urine: Concentration
How is concentration expressed?
What is specific gravity?
How is specific gravity measured?

A

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)
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16
Q

Specific Gravity: Ranges?
Low SG?
High SG?

A

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)
17
Q

Physical Examination of Urine: Volume

Normal vs not normal?

A

Normal: 600-2000 mL/day

Polyuria: >2 L/day: excessive liquid intake, diabetes mellitus or insipidus

Oliguria:

18
Q

What tests are read from a urine dipstick? (chemical analysis)

A 
Leukocyte Esterase
Nitrite
Urobilinogen
Protein
pH
Blood
Specific Gravity
Ketones
Bilirubin
Glucose
19
Q

Chemical principle behind Urine Dipstick: Glucose?

A

ll

20
Q

Uses and Limitations of Urine Glucose Detection?

A

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

21
Q

Describe the detection of Reducing Sugars by CuSO4.

A

l

22
Q

Urine Dipstick: Bilirubin

Describe the chemical principle behind this test.

A

l

23
Q

Uses and Limitations of Urine Bilirubin Detection

A 
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

24
Q

What is the Ictotest?

A
  • 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
25
Q

The Urine Dipstick: Urobilinogen

Chemical Principle?

A

l

26
Q

Uses and Limitations of Urobilinogen Detection

A

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

27
Q

Bilirubin negative, urobilinogen increased?

A

Prehepatic:

Increased heme degradation, hemolytic conditions, transfusion reaction, sickle cell disease

Ineffective erythropoiesis due to thalassemia or pernicious anemia

28
Q

Bilirubin positive, urobilinogen incr. or normal?

A

Hepatic:

hepatitis, cirrhosis, genetic defects

29
Q

Bilirubin positive, urobilinogen absent or low?

A

Posthepatic: obstruction, carcinoma, calculi, fibrosis

30
Q

The Urine Dipstick: Ketones

Chemical Principle?

A

l

31
Q

Uses and Limitations of Urine Ketone Detection?

A

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

32
Q

The Urine Dipstick: Specific Gravity

Chemical Principle?

A

l

33
Q

Uses and Limitations of Urine Specific Gravity

A

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

34
Q

Urine Dipstick: Blood

A

l

Clinical Chemistry (9 decks)

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