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Lecture: Chemical Pathology > Urinalysis > Flashcards

Urinalysis Flashcards

1
Q

How is urine formed?

A

by kidneys as ultrafiltrate of plasma

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2
Q

How much filtered plasma does the body convert into urine?

A

~170,000 mL of filtered plasma to ~1,200 mL urine

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3
Q

What is urine composed of?

A

95% H2O and 5% Solute
- organic substances: urea, creatinine, uric acid
- inorganic solids: sodium, chloride, potassium
- vitamins, hormones, medications

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4
Q

What is the normal daily urine output?

A

1200 - 1500 mL per day

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5
Q

What factors affect urine volume?

A

fluid intake, loss from nonrenal sources, antidiuretic secretion, necessity to excrete glucose/salts

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6
Q

oliguria

A

decrease in normal daily output (<400 mL/day) from dehydration, vomit, diarrhea, burns

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7
Q

anuria

A

cessation of urine flow from renal damage

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8
Q

polyuria

A

increase in daily volume (>2.5 L/day) from diabetes mellitus/insipidus, alcohol, diuretics

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9
Q

diabetes mellitus

A
  • defect in pancreatic insulin production causes increased body glucose concentration
  • kidney won’t reabsorb excess glucose; excess excretion of water to remove
  • urine appears dilute with high specific gravity and glucose
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10
Q

diabetes insipidus

A
  • decrease in production/function of antidiuretic hormone; water not reabsorbed from plasma
  • urine appears dilute with a low specific gravity
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11
Q

How is urine collected and handled?

A

tested within in two hours of collection; well-mixed

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12
Q

What happens when urine is unpreserved?

A
  • increased bacteria
  • decreased glucose, ketone, bilirubin, urobilinogen, RBC/WBC
  • reduced clarity from bacterial growth and amorphous precipitation
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13
Q

What temperature is urine preserved at?

A

2-8 C

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14
Q

What is the benefit of refrigerating urine?

A
  • decreases bacterial growth
  • increases specific gravity
  • precipitates amorphous crystals
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15
Q

What chemical preservatives are used for urine?

A

boric acid, chlorohexidine

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16
Q

What is a random void used for?

A

screening test (diet/activity dependent)

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17
Q

What is a first morning void used for?

A

concentrated for pregnancy and proteinuria detection

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18
Q

What is a 24-hour timed void used for?

A

quantitative urine chemistries

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19
Q

What is a midstream clean catch used for?

A

best type for bacterial culture and urinalysis

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20
Q

What is the normal color of urine?

A

light yellow to amber (urochrome)

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21
Q

What does a dark yellow/amber/orange urine with foam indicate?

A

bilirubin or protein

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22
Q

What does a dark yellow/amber/orange urine without foam indicate?

A

high urobilinogen-urobilin

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23
Q

What does a red and cloudy urine indicate?

A

RBCs

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24
Q

What does a red and clear urine indicate?

A

hemoglobin or myoglobin

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25
Q

What does a red (port-wine) urine with negative blood test indicate?

A

porphobilinogen-porphyrin oxidation

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26
Q

What does a brown urine indicate?

A

RBC in acidic urine (hemoglobin > methemoglobin oxidation)

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27
Q

What does a brown/black urine indicate?

A

melanin (malignant melanoma), homogentistic acid (alkaptonuria)

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28
Q

What does a blue/green urine indicate?

A

Pseudomonas species UTI

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29
Q

What are some non-pathologic reasons for a change in urine color?

A

menstrual, diet, medications

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30
Q

What does the clarity of a normal urine look like?

A

clear with no visible particulates

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31
Q

What does the clarity of an abnormal urine look like?

A

hazy, cloudy, turbid, milky

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32
Q

What are the non-pathologic elements that can be found in a turbid urine?

A

squamous epithelial cells, mucus, amorphous urates, amorphous phosphates

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33
Q

What are the pathologic elements that can be found in a turbid urine?

A
  • cellular: RBC, WBC, renal-transitional epithelial cells
  • microorganisms: bacteria/yeast
  • abnormal crystals
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34
Q

What is specific gravity assessing?

A

the kidney’s ability to reabsorb essential chemicals/water from glomerular filtrate

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35
Q

What is specific gravity?

A

the density of a solution compared with density of distilled water at equal temperatures/volumes

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36
Q

How does the strip reaction for specific gravity work?

A
  • polyelectrolyte on strip release hydrogen ions in a proportion to number of ions in solution
  • utilizes bromothymol blue indicator to measure pH change
  • as specific gravity, indicator changes from blue to green-yellow
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37
Q

What affects pH?

A

kidneys regulate acid-base content through secretion of hydrogen and reabsorption of bicarbonate in convoluted tubules

38
Q

How does the strip reaction for pH work?

A

double dye indicator methodology
- methyl red and hydrogen ions causes red to yellow
- bromothymol blue and hydrogen ions causes yellow to blue

39
Q

What is the clinical significance of acidic urine?

A

respiratory/metabolic acidosis; starvation, dehydration, diarrhea

40
Q

What is the clinical significance of alkaline urine?

A

respiratory/metabolic alkalosis; hyperventilation, vomiting

41
Q

What is proteinuria associated with?

A

early renal disease; most reabsorbed by tubules

42
Q

What are the major proteins?

A

albumin, immunoglobulins, Tamm-Horsfall, prostatic/vaginal secretions

43
Q

How does the strip reaction for protein work?

A

albumin accepts hydrogen ions from indicator causing yellow to blue-green color change while pad is kept at a constant pH of 3

44
Q

What is the clinical significance of renal proteinuria?

A
  • glomerular damage - selective filtration impaired causing serum albumin, RBC, WBC to pass through membrane into urine
  • tubular disorders - defective protein reabsorption (Fanconi’s, heavy metal toxicity, viral infections)
  • transient disorders - exercise, dehydration, stress, exposure to cold
45
Q

What is prerenal proteinuria?

A

conditions affecting plasma prior to reaching kidney

46
Q

What is the clinical significance of prerenal proteinuria?

A
  • overflow of hemoglobin, myoglobin, acute-phase reactants in inflammation exceeds normal reabsorptive capacity
  • Bence Jones Protein (multiple myeloma)
47
Q

What is postrenal proteinuria?

A

lower urinary tract adds proteins

48
Q

What is the clinical significance of postrenal proteinuria?

A

bacterial/fungal infections, menstrual/sperm contaminates

49
Q

What is microalbuminuria?

A

denotes protein not detected by urinalysis

50
Q

What is the clinical significance of microalbuminuria?

A

diabetic nephropathy in diabetes mellitus leads to eventual renal failure

51
Q

How does the glucose strip test work?

A

double sequential enzymatic reaction; glucose oxidase catalyzes reaction of glucose to form gluconic acid and peroxide, peroxidase causes peroxide and chromagen to form colored compound

52
Q

What filters glucose?

A

glomerulus

53
Q

What reabsorbs glucose after it is filtered?

A

proximal convoluted tubules

54
Q

What is the clinical significance of glucose values?

A
  • diabetes mellitus detection and monitoring
  • gestational diabetes: placental hormones block insulin action
  • hormonal function issues associated with pancreatitis, Cushing’s, hyperparathyroidism
  • advanced renal disease and Fanconi’s
55
Q

What is the copper reduction test (Clinitest)?

A

any reducing substances change copper sulfate to cuprous oxide causing color change (blue to orange/red); non-specific/detects all sugars

56
Q

What could the clinical significance of ketones be?

A
  • inability to metabolize carbohydrates (diabetes mellitus)
  • diabetes monitoring: ketouria shows insulin deficiency and need to regulate dose
  • loss of carbohydrates (vomiting)
  • inadequate carbohydrate intake (diet, starvation, malabsorption)
57
Q

How does the strip reaction for ketones work?

A

only acetoacetic acids reacts with sodium nitroprusside to produce purple color

58
Q

What is hematuria?

A

intact RBC found in urine (red/cloudy)

59
Q

What causes hematuria?

A

renal calculi, glomerulonephritis, pyelonephritis, tumors, trauma

60
Q

What is hemoglobinuria?

A

free hemoglobin in urine (red/clear)

61
Q

What causes hemoglobinuria?

A
  • haptoglobin complexes normally prevent filtration
  • RBC rupture in dilute, alkaline urine
  • intravascular hemolysis from transfusion reactions, hemolytic anemias, burns cause overload of free hemoglobin
62
Q

How does the strip reaction for blood work?

A
  • pseudoperoxidase activity of hemoglobin catalyzes reaction between hydrogen peroxide and chromagen to produce green-blue color
  • uniform color in presence of free hemoglobin or myoglobin
  • intact RBCs lyse on pad causing speckled pattern
63
Q

What could the clinical significance of bilirubin be?

A
  • early indicator of liver damage (hepatitis, cirrhosis)
  • bile duct obstruction (gallstones, cancer)
64
Q

How does the strip reaction for bilirubin work?

A

bilirubin glucuronide and diazonium salt react to produce azodye (tan to pink-violet color)

65
Q

What test is used as confirmation for bilirubin?

A

Ictotest

66
Q

Why is the Ictotest a confirmation test?

A

less subject to interference and more sensitive than strip

67
Q

What is the clinical significance of urobilinogen?

A
  • early detection of liver disease (decreased ability to process recirculated urobilinogen from intestine)
  • hemolytic disorders
68
Q

How does the strip reaction on a Multistix for urobilinogen work?

A

ehrlich’s aldehyde reaction (urobilinogen and ehrlich’s reagent make red color)

69
Q

How does the strip reaction on a Chemstrip for urobilinogen work?

A

diazonium salt reaction (urobilinogen and diazonium slat react to form red azodye)

70
Q

What happens in bile duct obstruction?

A

disruption of normal degradation process causes leakage of conjugated bilirubin into circulation

71
Q

What results might signify bile duct obstruction?

A

high positive bilirubin and normal urobilinogen

72
Q

What results might signify liver damage?

A

positive or negative bilirubin and postive urobilinogen

73
Q

What happens in hemolytic disease?

A

serum unconjugated bilirubin not excreted by kidneys

74
Q

What results might signify hemolytic disease?

A

negative bilirubin and high positive urobilinogen

75
Q

What does Watson-Schwartz Differentiation Test help differentiate?

A

differentiates between urobilinogen and porphobilinogen

76
Q

How does the Watson-Schwartz Differentiation Test work?

A

ehrlich reagent is added to urine, producing a cherry red color; divided into two tubes with chloroform and butanol
- urobilinogen: extracted into chloroform (clear top, red bottom), extracted into butanol (red top, clear bottom)
- porphobilinogen: not extracted by chloroform or butanol; opposite of above

77
Q

What is the clinical significance of nitrite?

A

serves as rapid screening test for urinary tract infection; early detection while patient is asymptomatic or no culture ordered

78
Q

How does the strip reaction for nitrite work?

A

diazonium salt reaction forms pink-colored azo dye

79
Q

What is the clinical significance of leukocyte esterase?

A

test designed for detection and not quantitation; screening test is cost-effective over cultures

80
Q

How does the strip reaction for leukocyte esterase work?

A

action of leukocyte esterase to catalyze acid ester on test pad to form aromatic compound; compound combines with diazonium salt to produce purple azo dye

81
Q

What could interfere with the specific gravity test?

A
  • only measures ionic solutes, not large organic molecules (glucose, urea), radiographic x-ray dyes, plasma expanders which cause differences between methods
  • alkaline urine pH interferes with bromothymol blue indicator and falsely lowers specific gravity
82
Q

What could interfere with protein test?

A
  • highly buffered alkaline urine which overrides constant pH buffer system
  • pigmented urine samples (phenazopyridine)
  • quaternary ammonium compounds, detergents (chlorohexidine)
83
Q

What could cause a false positive for the glucose test?

A

peroxide/detergents

84
Q

What could cause a false negative for the glucose test?

A

high specific gravity, low temperature, old sample, ascorbic acid (Vitamin C)

85
Q

What could interfere with ketone test?

A
  • false positive: dyes, Levodopa, MESNA Medications
  • false negative: old and unpreserved urine (volatile/bacterial utilization)
86
Q

What could interfere with blood test?

A
  • false positive: menstrual, oxidizing detergents, bacterial peroxidases
  • false negative: high ascorbic acid, high specific gravity with crenated cells that don’t lyse, no mixing of specimen
87
Q

What could interfere with bilirubin test?

A
  • false positive: highly pigmented urine (phenazopyridine)
  • false negative: exposure to light, high ascorbic acid or nitrite levels
88
Q

What could interfere with urobilinogen test?

A
  • false positive: highly pigmented urine, “ehrlich reactive compounds” (porphobilinogen) on Multistix only
  • false negative: old samples (photo-oxidized to urobilin), high nitrite, formalin
89
Q

What could interfere with leukocyte esterase test?

A
  • bacteria don’t produce enzyme reductase (gram-positive, yeast)
  • bacteria not in contact with urine long enough to produce nitrite
  • lack of dietary nitrate from green vegetables
  • nitrite reduced to nitrogen with large numbers of bacteria
  • false negative: high specific gravity, high ascorbic acid, antibiotics
  • false positive: improperly preserved sample, highly pigmented urine
90
Q

What could interfere with leukocyte esterase test?

A
  • false positive: strong oxidizers, formalin, highly pigmented urine
  • false negative: high levels of protein, glucose, ascorbic acid

Lecture: Chemical Pathology (9 decks)

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