Urinalysis Flashcards
How is urine formed?
by kidneys as ultrafiltrate of plasma
How much filtered plasma does the body convert into urine?
~170,000 mL of filtered plasma to ~1,200 mL urine
What is urine composed of?
95% H2O and 5% Solute
- organic substances: urea, creatinine, uric acid
- inorganic solids: sodium, chloride, potassium
- vitamins, hormones, medications
What is the normal daily urine output?
1200 - 1500 mL per day
What factors affect urine volume?
fluid intake, loss from nonrenal sources, antidiuretic secretion, necessity to excrete glucose/salts
oliguria
decrease in normal daily output (<400 mL/day) from dehydration, vomit, diarrhea, burns
anuria
cessation of urine flow from renal damage
polyuria
increase in daily volume (>2.5 L/day) from diabetes mellitus/insipidus, alcohol, diuretics
diabetes mellitus
- 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
diabetes insipidus
- decrease in production/function of antidiuretic hormone; water not reabsorbed from plasma
- urine appears dilute with a low specific gravity
How is urine collected and handled?
tested within in two hours of collection; well-mixed
What happens when urine is unpreserved?
- increased bacteria
- decreased glucose, ketone, bilirubin, urobilinogen, RBC/WBC
- reduced clarity from bacterial growth and amorphous precipitation
What temperature is urine preserved at?
2-8 C
What is the benefit of refrigerating urine?
- decreases bacterial growth
- increases specific gravity
- precipitates amorphous crystals
What chemical preservatives are used for urine?
boric acid, chlorohexidine
What is a random void used for?
screening test (diet/activity dependent)
What is a first morning void used for?
concentrated for pregnancy and proteinuria detection
What is a 24-hour timed void used for?
quantitative urine chemistries
What is a midstream clean catch used for?
best type for bacterial culture and urinalysis
What is the normal color of urine?
light yellow to amber (urochrome)
What does a dark yellow/amber/orange urine with foam indicate?
bilirubin or protein
What does a dark yellow/amber/orange urine without foam indicate?
high urobilinogen-urobilin
What does a red and cloudy urine indicate?
RBCs
What does a red and clear urine indicate?
hemoglobin or myoglobin
What does a red (port-wine) urine with negative blood test indicate?
porphobilinogen-porphyrin oxidation
What does a brown urine indicate?
RBC in acidic urine (hemoglobin > methemoglobin oxidation)
What does a brown/black urine indicate?
melanin (malignant melanoma), homogentistic acid (alkaptonuria)
What does a blue/green urine indicate?
Pseudomonas species UTI
What are some non-pathologic reasons for a change in urine color?
menstrual, diet, medications
What does the clarity of a normal urine look like?
clear with no visible particulates
What does the clarity of an abnormal urine look like?
hazy, cloudy, turbid, milky
What are the non-pathologic elements that can be found in a turbid urine?
squamous epithelial cells, mucus, amorphous urates, amorphous phosphates
What are the pathologic elements that can be found in a turbid urine?
- cellular: RBC, WBC, renal-transitional epithelial cells
- microorganisms: bacteria/yeast
- abnormal crystals
What is specific gravity assessing?
the kidney’s ability to reabsorb essential chemicals/water from glomerular filtrate
What is specific gravity?
the density of a solution compared with density of distilled water at equal temperatures/volumes
How does the strip reaction for specific gravity work?
- 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
What affects pH?
kidneys regulate acid-base content through secretion of hydrogen and reabsorption of bicarbonate in convoluted tubules
How does the strip reaction for pH work?
double dye indicator methodology
- methyl red and hydrogen ions causes red to yellow
- bromothymol blue and hydrogen ions causes yellow to blue
What is the clinical significance of acidic urine?
respiratory/metabolic acidosis; starvation, dehydration, diarrhea
What is the clinical significance of alkaline urine?
respiratory/metabolic alkalosis; hyperventilation, vomiting
What is proteinuria associated with?
early renal disease; most reabsorbed by tubules
What are the major proteins?
albumin, immunoglobulins, Tamm-Horsfall, prostatic/vaginal secretions
How does the strip reaction for protein work?
albumin accepts hydrogen ions from indicator causing yellow to blue-green color change while pad is kept at a constant pH of 3
What is the clinical significance of renal proteinuria?
- 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
What is prerenal proteinuria?
conditions affecting plasma prior to reaching kidney
What is the clinical significance of prerenal proteinuria?
- overflow of hemoglobin, myoglobin, acute-phase reactants in inflammation exceeds normal reabsorptive capacity
- Bence Jones Protein (multiple myeloma)
What is postrenal proteinuria?
lower urinary tract adds proteins
What is the clinical significance of postrenal proteinuria?
bacterial/fungal infections, menstrual/sperm contaminates
What is microalbuminuria?
denotes protein not detected by urinalysis
What is the clinical significance of microalbuminuria?
diabetic nephropathy in diabetes mellitus leads to eventual renal failure
How does the glucose strip test work?
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
What filters glucose?
glomerulus
What reabsorbs glucose after it is filtered?
proximal convoluted tubules
What is the clinical significance of glucose values?
- 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
What is the copper reduction test (Clinitest)?
any reducing substances change copper sulfate to cuprous oxide causing color change (blue to orange/red); non-specific/detects all sugars
What could the clinical significance of ketones be?
- 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)
How does the strip reaction for ketones work?
only acetoacetic acids reacts with sodium nitroprusside to produce purple color
What is hematuria?
intact RBC found in urine (red/cloudy)
What causes hematuria?
renal calculi, glomerulonephritis, pyelonephritis, tumors, trauma
What is hemoglobinuria?
free hemoglobin in urine (red/clear)
What causes hemoglobinuria?
- haptoglobin complexes normally prevent filtration
- RBC rupture in dilute, alkaline urine
- intravascular hemolysis from transfusion reactions, hemolytic anemias, burns cause overload of free hemoglobin
How does the strip reaction for blood work?
- 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
What could the clinical significance of bilirubin be?
- early indicator of liver damage (hepatitis, cirrhosis)
- bile duct obstruction (gallstones, cancer)
How does the strip reaction for bilirubin work?
bilirubin glucuronide and diazonium salt react to produce azodye (tan to pink-violet color)
What test is used as confirmation for bilirubin?
Ictotest
Why is the Ictotest a confirmation test?
less subject to interference and more sensitive than strip
What is the clinical significance of urobilinogen?
- early detection of liver disease (decreased ability to process recirculated urobilinogen from intestine)
- hemolytic disorders
How does the strip reaction on a Multistix for urobilinogen work?
ehrlich’s aldehyde reaction (urobilinogen and ehrlich’s reagent make red color)
How does the strip reaction on a Chemstrip for urobilinogen work?
diazonium salt reaction (urobilinogen and diazonium slat react to form red azodye)
What happens in bile duct obstruction?
disruption of normal degradation process causes leakage of conjugated bilirubin into circulation
What results might signify bile duct obstruction?
high positive bilirubin and normal urobilinogen
What results might signify liver damage?
positive or negative bilirubin and postive urobilinogen
What happens in hemolytic disease?
serum unconjugated bilirubin not excreted by kidneys
What results might signify hemolytic disease?
negative bilirubin and high positive urobilinogen
What does Watson-Schwartz Differentiation Test help differentiate?
differentiates between urobilinogen and porphobilinogen
How does the Watson-Schwartz Differentiation Test work?
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
What is the clinical significance of nitrite?
serves as rapid screening test for urinary tract infection; early detection while patient is asymptomatic or no culture ordered
How does the strip reaction for nitrite work?
diazonium salt reaction forms pink-colored azo dye
What is the clinical significance of leukocyte esterase?
test designed for detection and not quantitation; screening test is cost-effective over cultures
How does the strip reaction for leukocyte esterase work?
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
What could interfere with the specific gravity test?
- 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
What could interfere with protein test?
- highly buffered alkaline urine which overrides constant pH buffer system
- pigmented urine samples (phenazopyridine)
- quaternary ammonium compounds, detergents (chlorohexidine)
What could cause a false positive for the glucose test?
peroxide/detergents
What could cause a false negative for the glucose test?
high specific gravity, low temperature, old sample, ascorbic acid (Vitamin C)
What could interfere with ketone test?
- false positive: dyes, Levodopa, MESNA Medications
- false negative: old and unpreserved urine (volatile/bacterial utilization)
What could interfere with blood test?
- 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
What could interfere with bilirubin test?
- false positive: highly pigmented urine (phenazopyridine)
- false negative: exposure to light, high ascorbic acid or nitrite levels
What could interfere with urobilinogen test?
- false positive: highly pigmented urine, “ehrlich reactive compounds” (porphobilinogen) on Multistix only
- false negative: old samples (photo-oxidized to urobilin), high nitrite, formalin
What could interfere with leukocyte esterase test?
- 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
What could interfere with leukocyte esterase test?
- false positive: strong oxidizers, formalin, highly pigmented urine
- false negative: high levels of protein, glucose, ascorbic acid
