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AUBF > UA 2: CHEMICAL EXAMINATION OF URINE (PROTEIN, GLUCOSE) > Flashcards

UA 2: CHEMICAL EXAMINATION OF URINE (PROTEIN, GLUCOSE) Flashcards

1
Q

T/F:

only a few low molecular weight proteins are filtered out by the glomerulus

A

TRUE

  • small percentage should be found in urine; usually albumin
      • a (+) urine protein result requires additional testing to determine whether the protein represents a normal or pathologic condition
  • most LMW proteins are readily absorbed (eg. hemoglobin, myoglobin)
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2
Q

the major protein in the urine

A

Albumin

- others present in urine: serum microglobulin, proteins produced in the genitourinary tract

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3
Q

clinical proteinuria

A
  • > /= 30mg/dL CHON
  • causes can be grouped based on the origin of the CHONs:
    a. Pre-renal
    b. Renal
    c. Post-renal
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4
Q

proteinuria caused by conditions prior to reaching the kidneys

A

Pre-renal proteinuria

  • frequently transient
  • not indicative of renal disease
  • happens when the filtration of CHONs exceeds the normal reabsorptive capacity of renal tubules
      • result: overflow of CHONs in urine (incl. LMW CHONs, acute phase reactants, Bence-Jones protein)
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5
Q

proteins can be added to a urine specimen as it passes through the lower urinary tract

A

Post-renal proteinuria

  • CHONs added include:
      • exudates (from bacterial & fungal infections, inflammation)
      • blood (as a result of injury & menstrual contamination)
      • prostatic fluid
      • spermatozoa
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6
Q

Bence-Jones protein

A
  • found in patients with multiple myeloma (MM)
      • a proliferative disorder of the plasma cells
      • serum contains markedly high levels of monoclonal Ig light chains
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7
Q

determination of Bence-Jones protein

A
  1. Boil
  2. Filter
  3. Cool down to 60 or 40C
  4. Observe for turbidity
    - - turbid = positive for Bence-Jones protein
    - - clear = negative for Bence-Jones protein
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8
Q

proteinuria associated with true renal disease

A

Renal proteinuria

  • may be the result of either:
      • glomerular damage = affects filtration (up to 4g/day)
      • tubular damage = affects reabsorption (markedly increased CHONs in urine)
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9
Q

renal proteinuria caused by impaired filtration

A
  1. Glomerular proteinuria
  2. Microalbuminuria
  3. Orthostatic proteinuria
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10
Q

the glomerular membrane is damaged, resulting in impaired selective filtration

A

Glomerular proteinuria
- when selective filtration is impaired, high amounts of serum proteins, WBCs & RBCs pass through the membrane and are excreted in urine

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11
Q

major causes of glomerular proteinuria

A
  1. exposure to abnormal substances
    - eg. amyloid material, toxic substances, immune complexes (LE, streptococcal glomerulonephritis)
  2. increased pressure from blood
    - may override the selective rotation of the glomerulus
    - reversible
    - does not necessarily mean glomerular damage
    - caused by strenuous exercise, dehydration, hypertension
  3. pregnancy
    - glomerular proteinuria occurs during the latter months
    - may indicate a “pre-eclamptic state”
    - should be considered by the physician in conjunction with other clinical symptoms to determine if the condition exists
  4. other causes of benign proteinuria
    - transient (diminishes over time)
    - eg. high fever, exposure to colds
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12
Q

common occurrence in patients with Type I & II DM

A

Microalbuminuria

  • in TI & II DM patients, development of diabetic nephropathy is common
  • detection can predict the onset of renal complications
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13
Q

preventing the onset of renal complications

A

stabilizing blood glucose & control hypertension

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14
Q

T/F:

microalbuminuria is associated with increased risk of CVD

A

TRUE

- CVD = cardiovascular disease

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15
Q

detection of microalbuminuria

A

Measure albumin quantitatively

  • 24h specimen
  • significant results:
      • 30-300mg albumin/24h
      • albumin excretion rate = 20-200ug/minute
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16
Q

postural proteinuria

A

Orthostatic proteinuria

  • long periods spent in a vertical position is believed to cause pressure in the renal vein & override filtration –> benign proteinuria
  • common in young adults
  • disappears when horizontal position is assumed
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17
Q

detection of orthostatic proteinuria

A
  1. patients are requested to empty their bladder to before going to bed
  2. collect the first morning specimen
  3. collect a 2nd specimen hours after
    - patient should be in a vertical position
  4. test for CHONs
    - result for O. proteinuria:
    - - first morning spx = (-)
    - - 2nd spx = (+)
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18
Q

renal proteinuria caused by tubular damage

A
  • other LMW CHONs that are usually reabsorbed are present
  • causes:
      • exposure to toxic substances & heavy metals
      • severe viral infections
      • Fanconi syndrome
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19
Q

methods of protein determination

A
  1. reagent strip
  2. SSA precipitation test
  3. micral test
  4. immunodip
  5. albumin:creatinine ratio
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20
Q

reagent strip method principle & mode of measurement

A

Principle:
protein error of indicators (pH indicators)
- pH indicators have a characteristic color at certain pH levels
- color when there is no reaction: yellow

Mode of measurement:
colorimetric
- at constant acid pH (3.0), proteins in urine cause a changed color in the indicator resulting to an end color of blue to green
– end color depends on CHON concentration in urine

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21
Q

reading time for reagent strip method

A

60 seconds

*reagent strip method is more sensitive to albumin since it has more amino group

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22
Q

reagent strip brands most commonly used

A
  1. Multistix
    - reagent: Tetrabromophenol blue
    - sensitivity: 15-30mg/dL albumin
  2. Chemstrip
    - reagent: 3’,3”,5’,5”-tetrachlorophenol-3,4,5,6-tetrabromosulfophthalein
    - sensitivity: 6mg/dL albumin
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23
Q

interference/s to reagent strip method

A

Change in pH

  • the method highly depends on the pH indicators
  • main reaction interference would be any condition that changes the pH of the
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24
Q

sources of error in reagent strip method

A
  1. highly buffered alkaline urine
    - pH is set at 3.0 (acidic)
  2. prolonged contact with the reagent pad & urine
    - causes bleaching out of the reagent
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25
Q

causes false positive reagent strip result

A
  • highly buffered alkaline urine
  • prolonged contact with urine
  • contamination with quarternary ammonium compounds (QAC), detergents, antiseptics
  • specimens with high SG
  • highly pigmented urine
      • interferes with color reaction, not with the pH
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26
Q

causes false negative reagent strip result

A
  • presence of CHONs other than albumin

- microalbuminuria

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27
Q

Identify this test:

principle: cold precipitation

proteins detected: all forms

specimen required: centrifuged urine

A

SSA precipitation test

  • SSA = sulfosalicylic acid
  • centrifuged urine is used to remove any extraneous contamination
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28
Q

procedure for SSA precipitation test

A
  1. add 3mL of 3% SSA reagent to 3mL centrifuged urine
  2. mix by inversion
  3. observe for cloudiness
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29
Q

reporting of SSA turbidity

A

Negative

  • less than 6mg/dL
  • no increase in turbidity

Trace

  • 6-30mg/dL
  • noticeable turbidity

+ (1+)

  • 30-100mg/dL
  • distinct turbidty, NO GRANULATION

++ (2+)

  • 100-200mg/dL
  • turbidity, granulation, NO FLOCCULATION

+++ (3+)

  • 200-400mg/dL
  • turbidity, granulation, flocculation

++++ (4+)

  • > 400mg/dL
  • clumps of protein
30
Q

a new method for microalbuminuria testing that is specific for albumin

A

Micral test
- patient at risk for renal disease can be monitored using random or 1st morning specimens

Manufacturer:
Roache Diagnostics

Principle:
EIA

Sensitivity:
0-10mg/dL (0-100mg/L)

Specificity:
albumin

Specimen:
1st morning urine

31
Q

application time, reading time & end color of micral test

A

Application time:
5 seconds

Reading time:
1 minute

Color range:
white to red

End color:
red

32
Q

compositions of the micral test reagent strip

A
  1. Zone 1
    - conjugate matrix fleece
    - reagent gold-labeled anti-human albumin-enzyme conjugate
    - enzyme: B-galactosidase
  2. Zone 2
    - capture matrix fleece
    - human serum albumin
  3. Detection pad
    - substrate: chlorophenol red galactoside
33
Q

micral test procedure

A
  1. dip the strip into the urine
    - dip up to a level marked on the strip
    - hold for 5 seconds
  2. allow excess urine to drain
    - place strip on a neon absorbent surface OR across the top of the collection cup
    - wait for 1 minute
  3. compare the color of the reaction pad on the strip with the color scale on the test strip vial
34
Q

identify the test:

principle: immunochromography
specimen: first morning
specificity: albumin

A

Immunodip

  • manufactured by Sekisui Diagnostic
  • reagents: blue latex particles coated with anti-human albumin
35
Q

rationale of immunodip

A

Migration of bound and unbound particles

  • migration is controlled by the size of the particles
  • a blue band is first formed by the unbound particles
  • bound particles continue to migrate up the strip to form a second blue band

Therefore,

Top blue band = bound particles

Bottom blue band = unbound particles

36
Q

procedure for immunodip

A
  1. place the test device in the urine sample
    - wait for 3 minutes
    - urine level must be above the mark on the test device
  2. read results after 3 minutes
    - compare the color intensity of the bands against the manufacturer’s color chart
37
Q

interpret:

top band = present, faint
bottom band = present, dark

A

NEGATIVE

- presence of <1.2mg albumin/dL

38
Q

interpret:

top band = present
bottom band = present
band colors equal

A

BORDERLINE

- 1.2-1.8mg albumin/dL

39
Q

interpret:

top band = present, dark
bottom band = present, faint

A

POSITIVE

- 2.0-8.0mg albumin/dL

40
Q

interpret:

top band = absent
bottom band = present

A

INVALID

- no bands present = also invalid

41
Q

done by comparing albumin excretion to the consistent excretion rate of creatinine

A

Albumin:Creatinine ratio

  • estimation of 24h microalbumin excretion
  • albumin reading can be corrected for over-hydration & dehydration in a random sample
  • method: reagent strip
      • Clinitek Microalbumin reagent strips
      • Multistix Pro reagent strips
42
Q

A:C ratio:

reagent strip reaction for albumin

A

Principle:
dye-binding reaction

Indicator:
bis(3’3”-diiodo-4’4”-dihydroxy-5’5”-dinitrophhenyl)-3,4,5,6-tetrabromosulphonphthalen (DIDNTB)

Sensitivity:
8-15mg/dL (80-150mg/L)

43
Q

interference/s in the reagent strip reaction for albumin

A
  • visibly bloody urine
  • abnormally colored urine

*interferences cause change of color in the reagent pad

44
Q

other compositions of the reagent strip for albumin

A
  1. polymethyl vinyl
    - increases specificity of the reagent pad to albumin by decreasing the nonspecific binding of polyamino acids to the albumin pad
  2. bis-(heptapropylene glycol) carbonate
    - treatment with said substance prevents reaction interference by highly buffered alkaline urine
45
Q

A:C ratio:

reagent strip reaction for creatinine

A

Principle:
pseudo-peroxidase activity of copper-creatinine complexes

Reagents:

  • CuSO4
  • 3,3’,5,5’-tetramethyl-benzidine (TMB)
  • diisopropyl-benzene-dihydroxyperoxide (DBDH)

Normal Value:
10-300mg/dL

46
Q

interference/s in the reagent strip reaction for creatinine

A
  • visibly bloody urine
  • abnormally colored urine
  • intake of gastric acid-reducing medication (cimetidine (Tagamet))
47
Q

T/F:

urine contains large amounts of glucose

A

FALSE

  • only MINUTE AMOUNTS are present in urine
  • glucose in the blood is readily filtered by the glomerulus
  • most of the glucose is reabsorbed by ACTIVE TRANSPORT
  • renal threshold: 160-180mg/dL
      • represents the blood level of glucose at which tubular reabsorption stops
48
Q

the body produces (insulin, glucagon) in response to increased blood glucose

A

Insulin
- converts glucose to glycogen

  • HI = High blood glucose, Insulin released
  • GLow = Glucagon is released when blood glucose is Low
49
Q

opposing hormones

A
  • hormones that work in opposition to insulin
  • break down glycogen to glucose by glycogenolysis, resulting in an excess of glucose excreted in urine
  • hormones include:
      • glucagon
      • epinephrine
      • cortisol
      • tyrosine
      • growth hormone
  • occurs in disorders affecting hormonal functions eg:
      • pancreatitis
      • acromegaly
      • Gaucher’s syndrome
      • hyperthyroidism
      • pheochhromocytome
      • thyrotoxicosis
50
Q

effect of severe stress in urine glucose levels

A
  • body releases epinephrine
  • breaks down glycogen to glucose by glycogenolysis
  • blocks the secretion of insulin –> excess glucose excreted
51
Q

gestational diabetes

A
  • occurs during pregnancy & disappears after delivery
  • hyperglycemia & glycosuria occurs normally around the 6th month of pregnancy
  • women with this condition are prone to developing TII DM
52
Q

macrosomia

A
  • when excess glucose presented to the the baby is stored as fat
  • the baby is fat; baby is at risk for obesity & diabetes
  • some of the excess glucose enters the placenta
      • insulin cannot enter the placenta, so glucose cannot be converted to glycogen
53
Q

happens when reabsorption of glucose by the renal tubules is compromised

A

Renal glycosuria

  • caused by diseases:
      • end stage renal disease
      • cystinosis
      • Fanconi syndrome
  • renal threshold may also be lowered in pregnancy
      • BUT reabsorption is not impaired
54
Q

methods of urine glucose determination

A
  1. reagent strip

2. copper reduction test

55
Q

identify the test:

Principle: double sequential enzymatic reaction

Specificity: glucose

A

Reagent strip

  • “glucose oxidase reaction”
  • an indirect method; does not directly measure glucose
      • glucose oxidase catalyzes a reaction between glucose & room air, producing gluconic acid & peroxide
      • peroxidase catalyzes the reaction between the peroxide & a chromogen, forming an oxidized colored compound that is directly proportional to glucose concentration
56
Q

reagents used in the reagent strip for glucose

A
  • glucose oxidase
  • peroxidase
  • chromogen (depends on the brand)
      • Multstix: potassium iodide (KI)
      • Chemstrip: TMB
  • buffer
57
Q

end color of glucose reagent strip

A

a. Multistix
(+) = green
(-) = brown

b. Chemstrip
(+) = yellow
(-) = green

58
Q

reading & interpretation of reagent strip for glucose

A

a. Qualitative
- negative, trace, +, ++, +++, ++++

b. Quantitative
- 100mg/dL (.1%) to 2g/dL (2%)

59
Q

T/F:

reagent strips for glucose provide semi-quantitative measurements

A

TRUE

- only an estimate of the amount of glucose in the urine

60
Q

possible cause/s of false positive or false high glucose results

A

containers contaminated with peroxide or strong oxidizing reagents

61
Q

possible cause/s of false negative or false low glucose results

A
  • presence of strong reducing agents (eg. ascorbic acid)
  • increased ketone, SG
  • decreased temperature
  • bacterial degradation of glucose
62
Q

what to do to minimize interference from ascorbic acid?

A

incorporate strips with additional chemicals (eg. iodate) to oxidize ascorbic acid

63
Q

these also cause false positive or high results

A

Increased ketone, SG & low temperature

  • high levels of ketones are usually accompanied by marked glycosuria
  • high SG & low temp. may decrease the sensitivity of the test
64
Q

the greatest source of false negative error

A

Bacterial degradation of glucose

- as a result of allowing the specimen to remain unpreserved at room temperature for extended periods

65
Q

Benedict’s test

A

Copper reduction test
- can also be in tablet form (Clinitest)

Principle:
CuSO4 is reduced to Cu2O by reducing substances in the presence of alkali & heat

Reagents:

  • Benedict’s solution
      • copper sulfate
      • sodium carbonate
      • sodium citrate (buffer)
  • sodium hydroxide (in Clinitest tablet)
66
Q

Clinitest procedure

A
  1. add 5 drops of urine into a thick glass test tube placed in a rack
  2. add 10 drops of distilled H2O
  3. drop 1 Clinitest tablet & observe reaction until cessation of boiling
  4. wait for 15 seconds after conclusion of effervescence (bubbles)
  5. shake tube gently
  6. compare results to the color chart
    - ranges from blue (negative) to orange (positive)
    - report results in mg/dL or %
67
Q

“pass through” phenomenon

A
  • occurs at high glucose levels
  • the color produced pass through the orange or red stage quickly & returns to green-brown –> (-) result may be reported
68
Q

sensitivity of Clinitest

A

200mg/dL

- cannot be used as confirmatory test for glucose

69
Q

interference/s for glucose

A
  • other reducing sugars (galactose, lactose, fructose, maltose, pentoses)
  • ascorbic acid
  • certain drug metabolites
  • antibiotics (cephalosporins)
70
Q

storage & handling of Clinitest tablets

A
  • should be stored in tightly closed packages
  • tablets are very hygroscopic
      • tend to absorb moisture from the air
      • a strong, blue color in unused tablets signifies deterioration due to moisture & vigorous tablet fizzing
71
Q

clinical significance of copper reduction tests in children

A
  • usually performed on children up to 2 years old
  • screening for galactosemia
      • galactose in newborns = “inborn error of metabolism”
      • lack of galactose-1-phosphate uridyl transferase
      • galactose breakdown is prevented –> complications –> death
72
Q

T/F:

the appearance of other reducing sugars is usually of medical significance

A

TRUE

- lactose is frequently found in the urine of nursing mothers

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