What is Urinalysis (UA)?
“Urinalysis is the physical, chemical, and
microscopic examination of urine. It involves
a number of tests to detect and measure
various compounds that pass through the
urine.”
UA is the best way to physically examine
the kidney
http://www.nlm.nih.gov/MEDLINEPLUS/ency/article/003579.htm
What is UA?
95 % water, 5 % solids
3 main components :
Water
Urea
NaCl
Urine color pigments urochrome + urobilin
Intensity of color parallels degree of contamination
Preparation
Clean catch: clean-voided midstream specimen into non-sterile
container External genitalia should be cleansed (at least in females)
Urine is a body fluid, and should be handled as such Lab examination should occur within 30-60 minutes if held at room temperature
Should be at least 10-15 ml in volume to investigate
Evaluation of un-spun urine (appearance, sp. gravity, chemical
testing)
Centrifugation (2000-3000 rpm for 3-5 minutes) Decant supernatant, resuspend sediment in the urine that remains on the sides of
the tube, and place a drop on a clean slide for microscopic evaluation of sediment
Indications for UA
Suspect or confirm Urinary Tract Infection (UTI)
Rule out primary renal disease
Rule out systemic disease with renal
manifestations
Assess complications of hypertension
Assess presence or amount of endogenous or
exogenous excreted substances
Components of the Basic UA
Color / appearance
Chemistries Protein
Glucose
Ketones
Bilirubin / urobilinogen
Hemoglobin / blood
Nitrite
Leukocyte esterase
Specific gravity
pH
Microscopic exam
Cells / casts
Bacteria
Other organisms
Crystals
Other Tests
Gram stain
Urine Culture
Acid-fast stain
Protein electrophoresis
Antigen detection (immunofluorescence)
Visual Inspection of Urine
Color: usually light to dark yellow, depending on
concentration of the urinary pigments urochrome,
urobilin, and uroerythrin Color can be altered by:
Disease
Drugs
Food
Appearance: Turbidity: Can be due to cells, bacteria, or mucous
Amorphous phosphates (white precipitate) in alkaline urine, or amorphous
urates (pink precipitate) in acid urine
Abnormal Colors in Urine
Red:
Heme pigment or hematuria, drugs and food can also affect
Brown:
Heme pigment--hemeglobin or myoglobin
Orange/Yellow:
Bilirubin, urobilin but also carrots, pyridium, nitrofurantoin
White:
Pyuria, phosphates, chyluria, propofol
Abnormal Colors in Urine
Blue/Green: Methylene blue, propofol, amitriptyline, pseudomonas
UTI)
Black Hemoglobinuria, ochronosis—alkaptonuria (due to
excretion of homogentisic acid)
Purple: Urinary tract infections in chronically catheterized pts,
with alkaline urine
Red or Brown Urine
Common causes are hemoglobin (either free or
contained in RBCs) and myoglobin
All will be heme positive on dipstick
Centrifugation of the urine differentiates whether the
pigment is:
Contained within cells (hematuria) or represents
hemoglobinuria or myoglobinuria
Heme negative red urine certain drugs, food dyes,
and abnormal metabolites
Red to Brown Urine: Heme-Neg Dipstick
Medications:
Doxorubicin, Chloroquine, Deferoxamine, Ibuprofen, Iron
sorbitol, Nitrofurantoin, Phenazopyridine,
Phenolphthalein, Rifampin
Food dyes:
Beets , Blackberries, Food coloring
Metabolites:
Bile pigments, Homogentisic acid, Melanin,
Methemoglobin, Porphyrin, Tyrosinosis, Urates (pink and
turbid)
Specific Gravity (SG)
SG is the ratio of urine density compared to a
water standard
Sp gravity = mass of Uvol/mass of equivalent dH2Ovol
SG indirectly measures renal concentrating ability
Normal range 1.003-1.035
Is measured by dipstick or refractometer
Specific Gravity – Falsely Elevated
Excretion of radiopaque contrast media
Excessive proteinuria (as in nephrosis or
diabetes)
Excessive glycosuria
Refrigerated urine
Diagnostic Clues From Urine Odor
Volatile acids responsible for normal urine
odor
Specific odors & diagnoses:
Acetone: Diabetic Ketoacidosis (DKA)
Ammonia : Infection with urea breakdown
Maple Syrup Urine Disease
Asparagus or garlic ingestion
Causes of Increased Turbidity
Urate crystals in acid urine
Phosphates in alkaline urine
RBC's
WBC's
Bacteria
Vaginal secretions
Fat globules
Urine pH
Range 4.6-8 ; normal =
6
Animal protein diet :
acid urine
Vegetable / fruit diet :
alkaline urineStones that develop in
acid urine: Uric acid Cysteine Calcium oxalate
Stones that develop in
alkaline urine:
Calcium phosphate
Calcium carbonate
Mg PO4
Protein Analysis
Normal urine contains small amounts of albumin &
globulin
Proteinuria exists if > 20 mg/dl Incidence 6 to 9 % in asymptomatic patients
Dipstick tests use tetrabromophenol blue indicator
system (yellow to green as concentration ↑)
React mainly with albumin
False positive with quaternary ammonia compounds &
phenazopyridine dyes
Sulfosalicylic Acid Test (SSA)
SSA detects all proteins in the urine
The acid denatures existing proteins and causes
them to come out of solution ↑ turbidity Useful for detecting immunoglobulin light chains
(multiple myeloma), especially where the albumin
dipstick is negative or trace
Radio-contrast agents can cause false positive results,
as can any substance precipitated by acid
(cephalosporins, penicillins, sulfonamides)
Glucose Analysis
Based on reduction of metal ions by glucose
False positive reactions due to : Hypochlorite or chlorine
Other sugars (galactose, lactose, fructose, maltose, as during
pregnancy)
Enzyme - based tests (glucose oxidase) are more
specific for glucose
Can have false negative results with ascorbic acid,
tetracycline, or high uric acid
Reading Glucose mg/dl
Negative 0
Trace 100
1+ 250
2+ 1000
3+ 2000
4+ >2000
Correlation of Urine Glucose Readings
Hemoglobin Analysis
Dipsticks for hemoglobin can detect 1-2 RBC per
hpf Detects heme protein: both hemoglobin and myoglobin
Uses pseudoperoxodase activity of Hgb to oxidize a
chromogen
Free Hgb gives uniform color; intact RBC give a
speckled pattern
False positive results can occur with alkaline urine,
contamination with oxidizing agents, presence of semen
Ketones
Choices are: Acetest, test tube, dipstick
All use reaction between acetoacetic acid &
nitroprusside to make a violet dye complex
Acetone reaction is < 5 % of color change
Beta-hydroxybutyrate not detected
Causes of False Positive Ketones
Levodopa
Phenolphthalein (in laxatives)
Insulin
Pyridium (phenazopyridine)
Phenformin
Phenylketonuria
Nitrate Analysis
Nitrites are absent from normal urine
Most UTI bacteria reduce urinary nitrates to nitrites
Dipstick uses aromatic amine & diazonium compound to
produce pink color in presence of nitrite
False negatives :
High urine flow (dilutional) ; Frequent or continuous (foley)
voiding
Ascorbic acid
Bacterial inhibition with antibiotics
Leukocyte Analysis
Any purple color on dipstick indicates > 5
WBC's/hpf
Detects intact & lysed WBC's + WBC casts
False negatives : Cephalexin, gentamicin, nitrofurantoin
Up to 97 % sensitivity & 90 % specificity for
culture - proven UTI's
Bacterial Counts
< 1000 colonies per/ml implies only
contamination
Counts > 1000 and < 100,000 per/ml may
imply infection
Counts > 100,000 / ml imply infection
Cellular Casts
Represents contents of renal tubules
discharged into urine
Cast types & associated diseases :
Broad, epithelial, fatty, granular, or waxy :
parenchymal renal disease
RBC : acute glomerulonephritis
WBC : pyelonephritis
Cellular Casts
RBC casts Usually represent significant glomerular disease
Can occur after very strenuous exercise
Hyaline casts Clear, colorless ; due to protein precipitation
Occurrence depends on urine flow, pH, degree of proteinuria
Granular casts Result from disintegration of cell material into particles
Form waxy casts when renal failure is advanced
Urinary Crystals
Normal crystals in acid pH: amorphous urates,
uric acid, calcium oxalate, sodium urate, hippuric
acid
Normal crystals in alkaline pH: amorphous
phosphate, triple phosphate, calcium phosphate,
ammonium biurate, calcium carbonate
Abnormal crystals in urine found in acid pH:
cystine, cholesterol, tyrosine , leucine, billirubin
Urine Electrolytes
Clinical situations where measurements useful :
Sodium
Volume depletion, acute oliguria, hyponatremia (R/O SIADH)
Chloride
Determine if metabolic alkalosis is chloride resistant or
sensitive
Potassium
Determine site of K+ loss in hypokalemia (if < 10 meq/liter,
implies GI tract as source)
Urine Culture
All children (age < 14) and all males
Women with history of : Immunocompromised
Renal abnormalities
Diabetes mellitus
Recent instrumentation and indwelling catheter
Prolonged Symptoms before seeking care
3 or more ( ? > 5 ) UTI's in last year
Recent pyelonephritis
Recent hospitalization