Urinalysis and other Renal Labs
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
 Specific gravity
 Chemistries
 pH

Protein

Glucose

Ketones

Bilirubin / urobilinogen

Hemoglobin / blood


 Microscopic exam

Cells / casts

Bacteria
Nitrite

Other organisms
Leukocyte esterase

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 urine
 Stones 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
Correlation of Urine Glucose Readings
Reading
Negative
Trace
Glucose mg/dl
0
100
1+
250
2+
1000
3+
2000
4+
>2000
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


Chloride


Volume depletion, acute oliguria, hyponatremia (R/O SIADH)
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
Renal Function Tests
Physiology of Creatinine
 Is the breakdown product of creatine (the storage source
for high-energy phosphate in muscle cells)
 CPK acts to add high energy phosphate to creatine from
ATP
 Creatine-phosphate transfers the phosphate to re-make
ATP when energy is needed for metabolism