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Clinical Chemistry 2 > 8 Urinalysis > Flashcards

8 Urinalysis Flashcards

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1
Q

Why perform urinalysis?

A
  1. Easy to collect
  2. Readily available
  3. Average daily output is 1200 mL
  4. Simple to test
  5. Testing methods are generally low cost
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2
Q

What can a urinalysis tell the doctor in general?

A

Results can provide information about status of carbohydrate metabolism, kidney and liver function, acid-base balance, and urinary tract infections

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3
Q

What does urine content vary with?

A

Varies with diet, nutritional status, metabolic rate, physical activity, endocrine function, body position and state of body and kidney.

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4
Q

What is the general composition of urine?

A
  1. 95% water and rest dissolved toxic end products of metabolism including salt, urea and creatinine
  2. May contain a few squamous cells from the urethra lining
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5
Q

What may form in urine in a container at room temperature?

A

Crystals may form at room temp

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6
Q

What are the different types of urine specimens that can be collected and for what purpose?

A

Types of Urine Specimens:
1. Random: Common, Simple screen but may be dilute and erroneous
2. First morning: Concentrated, Pregnancy Test, Preferred sample for urinalysis, Urine elements are more concentrated
3. Clean Catch: Can be used for urinalysis (<2hr) and cultures
Culture first! No preservative; refrigerate
4. Catheterized: Collected using catheter inserted through urethra into bladder
5. 24 hour: Timed specimen, May use preservative and requires refrigeration, Normal ~1.5 L/day

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7
Q

What is the normal colour of urine?

A

Normal urine is yellow from straw to amber
Very pale urine = dilute
Strong amber = concentrated

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8
Q

What can a non normal colour of urine indicate?

A
  1. Colouring might be related to vegetables (UTI or beets), dyes, infection (green with Pseudo), or drugs
  2. Red or pink = could be presence of RBCs
  3. Brown or orange = presence of bilirubin
  4. Red or purple = porphyrins
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9
Q

If normal urine is clear, what does it indicate if the urine is turbid?

A

Normal urine is clear

If urine is turbid it indicates the presence of particles or precipitate in urine. Could be bacteria, WBCs, fats, etc.

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10
Q

Should you smell the urine you are testing? If not, what should fresh urine, urine with ketones, old urine and someone with MSUD’s urine smell like?

A 
Don’t purposely smell the urine you are examining!
Fresh urine should have no odour
Fruity smell = presence of ketones
Ammonia smell = old urine
Maple syrup smell = MSUD
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11
Q

Is foam clinically tested? What clinical conditions can foam indicate?

A

Not clinically tested
Foam can indicate the presence of protein
Yellow foam could be bilirubin

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12
Q

What is a chemical urine test strip test?

A
  1. Multiple reagent pads impregnated with chemicals on a single plastic strip.
  2. Each reagent pad is absorbent. Contact with urine produces a chemical reaction that results in a colour change.
  3. Colours are compared to a colour chart. Can be done visually OR Process has become automated using Reflectance Spectrophotometry.
  4. Intensity of colour is proportional to the amount of substance present –> Semi-quantitative.
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13
Q

Why should you limit the number of strips removed for chemical strip urine testing?

A

Take out only the number of strips you are using immediately and cap container to preserve integrity

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14
Q

How should a chemical strip urine test be performed?

A
  1. Mix urine sample thoroughly
  2. Dip the strip completely into well-mixed, uncentrifuged, room temperature urine sample. Note: If the urine is going for culture and sensitivity (Microbiology Department) you should aliquot it first!
  3. Prolonged immersion may wash out reagents
  4. Remove excess urine from the strip by touching the edge against the container as it is withdrawn from the sample. Hold strip horizontal so chemicals do not run into each other.
  5. Wait for the reaction to occur
  6. Refer to package insert for the specific strips you are using
    Too short or too long from dipping time can lead to invalid results.
  7. Compare the colour reaction with the manufacturers chart for interpretation
  8. Read and record your results

Review also the automated procedure.

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15
Q

How should the urine strips and urine be stored for quality results?

A

Store urine strips in a cool place in a tightly closed container
Store urine in refrigerator if not done in 1-2 hours

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16
Q

What quality control measures besides proper storage needs to be considered for urine strip testing?

A
  1. Do not use past the expiration date or if the pads become discoloured
  2. Automated urinalysis instrument must be calibrated
  3. Test reagent strips with controls daily or when opening a new bottle
  4. Record all control values and reagent lot numbers
  5. Standard reporting format
  6. Identification of critical values
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17
Q

What does the chemical leukocyte test typically indicate and what may it correlate to?

A
  1. Presence of WBCs may indicate an infection. Will detect lysed WBCs.
  2. Usually correlates with a the presence of bacteria and a positive nitrite test. Note: Infections with yeast or parasites will not.
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18
Q

What can cause the leukocyte reagent strip reaction to have false positives or false negatives?

A

False positive:
Strong oxidizing agents
Formaldehyde
False negative:
↑ [ ] of protein, glucose, oxalic acid, and ascorbic acid
Lymphocytes do not produce leukocyte esterase

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19
Q

What is the principal of the leukocyte test strip pad?

A

Principle: Leukocyte esterase

Indoxylcarbonic acid ester (via Leukocyte Esterase)
→ Indoxyl + Acid
Indoxyl + Diazonium salt → Violet azole dye

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20
Q

What does the nitrite pad on the reagent strip indicate and how?

A

Indicator of urinary tract infection

Bacteria converts nitrates to nitrites

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21
Q

By what principle is the nitrite reaction performed on the reagent strip?

A

Principle: Griess reaction
1. Nitrite reacts in an acid medium with an aromatic amine in order to form a diazonium salt that in turn reacts with tetrahydrobenzoquinoline to produce a pink azo dye.

Aromatic amine + NO2 → Diazonium salt (nitrite)
Diazonium salt + tetrahydrobenzoquinoline → Pink azo dye

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22
Q

What can cause false positives and false negatives on the nitrate reagent pad?

A

False positive:
Improper storage
Incorrect collection technique
False negative:
Non-nitrate reducing bacteria (ie. g+c)
Large numbers of bacteria can reduce nitrite right to nitrogen
gas

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23
Q

How is conjugated bilirubin excreted in the urine as urobilinogen?

A
  1. Conjugated bilirubin excreted by the bile duct is converted by intestinal bacteria into urobilinogen.
  2. Some urobilinogen is reabsorbed in the intestine and circulated in the blood to the liver where it is excreted
  3. A small part of the urobilinogen is filtered out by the kidneys and appears in the urine
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24
Q

What can a measurement of urobilinogen possibly indicate?

A

Urobilinogen:
Indicators of systemic disorder of liver function
Damage, cirrhosis, hepatitis or obstruction

25
Q

What principle of measurement is done for urobilinogen?

A

Principle: Ehrlich’s Reaction

Urobilinogen + p-dimethylaminobenzaldehyde acidic environment→ Red dye

26
Q

What are possible causes for false positives and false negatives when measuring urobilinogen on a reagent strip?

A

False positive:
Porphobilinogen and indole
False negative:
Improper storage

27
Q

What does the protein urine reagent strip primarily identifies?

A

Strip primarily identifies albumin

28
Q

What is the clinical term for protein in urine and what can it indicate?

A

Protein in urine is referred to as proteinuria

  • Can indicate renal disease with glomerular or tubular damage
  • Protein filtered by kidney is usually reabsorbed
29
Q

What is a benign reason for having protein in urine?

A

Strenuous exercise can lead to protein in the urine.

30
Q

What is the principle of protein measurement on the urine reagent strip?

A

Principle: Protein error-of-indicators to produce a visible colorimetric reaction. Protein (primarily albumin) accept hydrogen ions from the indicator. The test is more sensitive to albumin because albumin contains more amino groups to accept the H+ ions than other proteins.

At a constant pH, the development of a green colour is due to the presence of protein.

31
Q

What can cause false positives on a protein urine reagent strip?

A

False positive:

  1. Highly pigmented urine
  2. Contamination of the container with detergents and antiseptics
  3. Highly alkaline urine
32
Q

What is the reference range for pH of normal urine?

A

Normal urine has a wide pH range between 5.0 and 8.0, therefore, no reference values

33
Q

What is the general difference in pH from first morning samples to samples taken after a meal?

A

First morning samples are slightly acidic; after a meal urine is more alkaline

34
Q

What can alkaline and acidic urine indicate?

A

Alkaline urine can indicate an infection, metabolic disorder, drugs, vegetarian diet, or old urine.

Acid urine can indicate metabolic disorders such as DKA or diet high in meat.

35
Q

What is the principle of the pH measurement reagent strip reaction?

A

Principle: Double indicator system of methyl red (colour change from red to yellow with pH between 5-6) and bromothymol blue (colour change from yellow to blue with pH between 6-9)

36
Q

What are the terms for RBCs and lysed RBCs in the urine?

A 
Presence of RBCs in the urine (hematuria) or 
lysed RBCs (hemoglobinuria).
37
Q

What are the two different presentation of RBCs in the urine and the macroscopic appearance of urine?

A

RBC’s present = red and “dense” (whole cells); Hemoglobin = red and clear
Both detected by strip but will only see intact RBCs with microscopic examination

38
Q

What is the principle that RBCs are measured on a urine reagent strip?

A

Principle: Pseudoperoxidase activity of hemoglobin catalyzes a reaction between the heme component of hemoglobin and the chemical indicator tetramethylbenzidine
H2O2 + tetramethylbenzidine → Oxidised tetramethylbenzidine (coloured) + H2O

39
Q

What causes false positive and false negative readings of RBC/blood measurement using a urine reagent strip?

A

False-positive:

  • Menstrual blood
  • Strong oxidizing detergents present in the specimen container.

False-negative:

  • High SG crenates RBCs
  • Formalin contamination
  • Improper mixing, RBCs settle to bottom
40
Q

What does specific gravity measure and what is its clinical significance?

A
  1. A measure of the amount of dissolved substances in a solution
    2 a) Indicates the kidneys ability to regulate fluids in patient’s with excess hydration or dehydration
    b) Low (< 1.005) in dilute urine; high (>1.020) in concentrated urine or urine samples with matter such as proteins, cells, glucose, etc.
41
Q

By what principle is specific gravity measured in urine using reagent strips?

A

Principle: Dissociation of electrolytes in an alkaline medium causes the release of hydrogen ions proportional to the number of cations present. The hydrogen ions will combine with bromothymol blue creating a colour change from blue to yellow.

42
Q

Besides reagents strips what other methods are there for measuring specific gravity of urine?

A

Refractometry and osmometry are also used as measurement methods

43
Q

What are ketones (for review) and what is the term for ketones in the urine?

A
  1. Product of fat metabolism not normally detected in blood and urine
  2. Ketones found in urine referred to as ketonuria

Three types: acetone, acetoacetic acid, and β-hydroxybutyric acid
Acetoacetic acid is the one measured in the test strip

44
Q

What is the clinical significance of ketones in urine?

A

May be present in clinical conditions like T1DM, starvation, malabsorption, etc.

45
Q

What is the principle of measurement of ketones using urine reagent strips?

A

Principle: Acetoacetic acid in an alkali medium reacts with sodium nitroprusside producing a magenta coloured complex

Acetoacetic acid + sodium nitroprusside alkaline environment→ magenta colour

46
Q

What can cause false positives and false negatives when measuring ketones with a urine reagent stirp?

A

False-positive:
Sulfhydryl containing drugs
False-negative:
Volatile ketones leave sample or are degraded by bacteria in improperly stored samples

47
Q

What is bilirubin and what is the its excreted form?

A

Bilirubin is a normal product resulting from the breakdown of RBCs; excreted as the conjugated form (what is detected on the strip)

48
Q

What does bilirubin in the urine indicate?

A

Indicator of systemic disorder of liver function

Damage, cirrhosis, hepatitis or obstruction

49
Q

What other measurement should bilirubin correlate to?

A

Should correlate with urobilinogen result

50
Q

What is the principle of measurement of bilirubin on a urine reagent strip?

A

Principle: Bilirubin combines with a diazonium salt in an acid medium to produce an azo dye that turns from pink to violet

51
Q

What can cause false positives and false negatives for a bilirubin measurement on a reagent strip?

A

False positive:
- Pigmented urine

False negative:

  • Light exposure in improperly stored samples
  • Ascorbic acid
52
Q

How does urine bilirubin and urine urobilinogen amounts change as someone goes from a normal state to a, pre-hepatic jaundice or a hepatic jaundice or a post-hepatic jaundice state?

A
  1. Normal State
    Urine Bilirubin - Neg
    Urine Urobilinogen - Small amount
  2. Pre-hepatic Jaundice (Hemolytic Disease)
    Urine Bilirubin - Neg
    Urine Urobilinogen - Increased
  3. Hepatic Jaundice (Hepatocellular Disease)
    Urine Bilirubin - Pos
    Urine Urobilinogen - Increased
  4. Post-hepatic Jaundice (Biliary Obstruction, e.g. gall stone)
    Urine Bilirubin - Pos
    Urine Urobilinogen - Normal to decreased
53
Q

What is glucose in urine referred to as and what is the renal threshold?

A

Glucose in urine is referred to as glucosuria (should not normally have glucose in urine)
Remember: Renal threshold 10.0 mmol/L

54
Q

What can glucose in urine indicate clinically? What other results may correlate?

A
  1. Could be found in clinical conditions like Diabetes Mellitus, adrenal tumours, or during strenuous exercise
  2. Patient’s with diabetes may also have increased ketones and proteins
55
Q

What is the principle of glucose measurement on urine reagent strips?

A

Principle: Glucose oxidase reaction

Glucose + O2 + H2O Glucose Oxidase→ gluconic acid + H2O2
H2O2 + reduced chromogen Peroxidase→ oxidized chromogen + H2O

56
Q

What can produce false positives and false negatives in glucose reagent strip measurements?

A

False positive:
- Strong oxidizing agents or peroxide from disinfectants contaminating sample container

False negative:

  • Ascorbic acid
  • Improper storage leading to bacterial glycolysis
57
Q

What measurement parameters increase and why when using urine reagents strips as unpreserved urine sits prior to testing?

A

Unpreserved urine changes that result in increases:

  1. pH - urea breakdown to ammonia by urease producing bacteria.
  2. Nitrite - bacterial reduction of nitrate.
  3. Bacteria - growth over time.
  4. Turbidity - Bacterial growth and precipitation of amorphous matter.
  5. Colour (darker) - oxidation or reduction of metabolites.
  6. Odour - Ammonia smell from bacterial breakdown of urea.
58
Q

What measurement parameters decrease and why when using urine reagents strips as unpreserved urine sits prior to testing?

A

Unpreserved urine changes that result in decreases:

  1. Glucose - glycolysis by bacteria..
  2. Ketones - volatile and bacterial destruction.
  3. Bilirubin - light exposure.
  4. Urobilinogen - oxidation to bilirubin
  5. RBCs, WBCs, & Casts - disintegrate (especially in alkaline urine)
  6. Clarity - growth of bacteria and ppt of amorphous material.

(ppt = precipitate?)

Clinical Chemistry 2 (13 decks)

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