PHYSICAL EXAMINATION OF URINE CHAPTER 4

Learning Objectives Upon completing this chapter, the reader will be able to List the common terminology used to report normal urine color. Discuss the relationship of urochrome to normal urine color. State how the presence of bilirubin, biliverdin, uroerythrin, and urobilin in a specimen may be suspected. Discuss the significance of cloudy, red urine and clear, red urine. Name two pathologic causes of black or brown urine.

Learning Objectives (cont’d) Discuss the significance of phenazopyridine in a specimen. State the clinical significance of urine clarity. List the common terminology used to report clarity. Describe the appearance and discuss the significance of amorphous phosphates and amorphous urates in freshly voided urine. List three pathologic and four nonpathologic causes of cloudy urine. Define specific gravity, and tell why this measurement can be significant in the routine analysis.

Learning Objectives (cont’d) Describe the principles of the refractometer, reagent strip, and osmolality for determining specific gravity. Given the concentration of glucose and protein in a specimen, calculate the correction needed to compensate for these high-molecular-weight substances in the refractometer specific gravity reading. Name two nonpathogenic causes of abnormally high specific gravity readings using a refractometer. Describe the advantages of measuring specific gravity using a reagent strip and osmolality. State possible causes of abnormal urine odor.

Introduction Physical examination of urine includes Results provide Color Clarity Specific gravity Results provide Preliminary information Correlation with other chemical and microscopic results

Physical Characteristics Provides preliminary information concerning disorders such as Glomerular bleeding Liver disease Inborn errors of metabolism Urinary tract infection Renal tubular function

Color Ranges from colorless to black Normal variations caused by Normal metabolic functions Physical activity Ingested materials Pathologic conditions Abnormal variations caused by Bleeding Liver disease Infection

Normal Urine Color Common terminology Pale yellow, yellow, dark yellow Should be consistent within institution Urochrome is pigment causing yellow color Normally excreted at a constant rate Increased in thyroid disorders and fasting Increases when specimen sits at room temperature Provides estimate of body hydration Pale yellow to dark yellow can be normal

Normal Urine Color (cont’d) Additional pigments uroerythrin, urobilin Color changes in older specimens Uroerythrin Pink pigment Attaches to amorphous urates formed in refrigerated specimens Urobilin Oxidation of normal constituent, urobilinogen Orange-brown color in older specimens

Abnormal Urine Color Many colors and causes Often reason patient comes to the physician Common abnormal colors Dark yellow/amber/orange Red/pink/brown Brown/black Blue/green

Dark Yellow/Amber/Orange Dark yellow and amber Normal = concentrated urine Abnormal = bilirubin Bilirubin indicates possible hepatitis virus present Standard precautions Foam Bilirubin produces yellow foam when shaken Normal urine produces small amount of white foam caused by protein

Dark Yellow/Amber/Orange (cont’d) Photooxidation of large amounts of urobilinogen produces yellow-orange urine No yellow foam when shaken Photooxidation of bilirubin to biliverdin produces yellow-green urine

Dark Yellow/Amber/Orange (cont’d) Phenazopyridine (pyridium) or Azo-Gantrisin for urinary tract infection produces thick orange pigment and yellow foam (no bilirubin) Thick pigment is noticeable, obscures natural color, and interferes with reagent strips

Red/Pink/Brown Blood is a common cause of red urine Methemoglobin Color can range from pink to brown Pink = small amount of blood Brown = oxidation of hemoglobin to methemoglobin Methemoglobin RBCs remaining in acid urine Fresh brown specimen can indicate glomerular bleeding Cloudy red urine = RBCs Clear red urine = hemoglobin/myoglobin Hemoglobin In vivo lysis of RBCs Patient’s plasma will also be red Consider in vitro lysis/specimen handling

Red/Pink/Brown (cont’d) Myoglobin Breakdown of skeletal muscle Fresh urine is often more reddish/brown Patient’s plasma is clear Port wine–colored urine Oxidation of porphobilinogen to porphyrias Nonpathogenic red urine Menstrual contamination Pigmented foods Medications (rifampin, pheno-compounds) Fresh beets Genetically susceptible people in alkaline urine Black raspberries in acid urine

Brown/Black Additional testing for specimens that Melanin Turn black after standing at room temperature Test negative for blood Melanin Excess in malignant melanoma Oxidation of melanogen to melanin Homogentisic acid Black color in alkaline urine Alkaptonuria Medications, levodopa, phenol derivatives, flagyl

Blue/Green Urinary and intestinal bacterial infections are the pathogenic cause Urinary: pseudomonas infection Intestinal: infection causing increased urinary indican oxidizing to indigo blue Catheter bags: purple color from Klebsiella, Providencia, and indican IV phenol medications cause green Clorets (green) medications: Robaxin, methylene blue, Elavil (blue)

Color and Clarity Procedure Use a well-mixed specimen View through a clear container View against a white background Maintain adequate room lighting Evaluate a consistent volume of specimen Determine color and clarity

Clarity Refers to the transparency or turbidity of a specimen Normal reporting Clear, hazy, cloudy, turbid, milky Visual examination Gently swirl specimen in a clear container in front of a good light source Automated turbidity readings are available Fresh clean-catch urine is normally clear

Urine Clarity Clear: No visible particulates, transparent Hazy: Few particulates, print easily seen through urine Cloudy: Many particulates, print blurred through urine Turbid: Print cannot be seen through urine Milky: May precipitate or be clotted

Nonpathogenic Turbidity Hazy female specimens with squamous epithelial cells and mucus Bacterial growth in nonpreserved specimens Refrigerated specimens with precipitated amorphous phosphates (white) and urates (pink) Contamination: fecal, talc, semen, vaginal creams, IV contrast media

Pathologic Turbidity Most common: RBCs, WBCs, bacteria Also: nonsquamous epithelial cells, yeast, abnormal crystals, lymph fluid, lipids The extent of turbidity should correspond to the amount of material observed in the microscopic examination Clarity is one of the criteria considered in determining the necessity of performing a microscopic examination

Specific Gravity (SG) Evaluation of urine concentration Determines if specimen is concentrated enough to provide reliable screening results Definition: the density of a solution compared with the density of an equal volume of distilled water at the same temperature

Specific Gravity (SG) (cont’d) Isosthenuric: SG of 1.010 (the SG of the plasma ultrafiltrate) Hyposthenuric: SG lower than 1.010 Hypersthenuric: SG higher than 1.010 Normal random specimen range 1.003 to 1.035; most common 1.015 to 1.025 Below 1.003 may not be urine Consistent low readings: further testing

Refractometer Measures velocity of light in air versus velocity of light in a solution Concentration changes the velocity and angle at which the light passes through the solution Prism in the refractometer determines the angle that light is passing through the urine and converts angle to calibrated viewing scale

Refractometer (cont'd)

Refractometer (cont’d) Advantages Temperature compensation not needed Light passes through temperature-compensating liquid Compensated between 15°C and 38°C Small specimen size: one or two drops

Glucose and Protein Corrections Subtract 0.003 for each gram of protein present Subtract 0.004 for each gram of glucose present Protein or glucose concentration can be determined from the chemical reagent strip tests

Correction Example A specimen containing 1 g/dL protein and 1 g/dL glucose has a specific gravity reading of 1.030 Calculate the corrected reading 1.030 – 0.003 (protein) = 1.027 – 0.004 (glucose) = 1.023 corrected specific gravity

Methodology Drop of urine placed on prism Focus on light source, and read scale Wipe off prism between specimens Calibration Distilled water should read 1.000; adjust set screw if necessary 5% NaCl should read 1.022 ± 0.001 9% sucrose should read 1.034 ± 0.001

Clinical Correlations Abnormally high results = >1.040 Radiographic contrast media (IVP) Dextran, other IV plasma expanders Check patient’s clinical course/history Reagent strip readings and osmometry not affected by high-molecular-weight substances Should be used as an alternative if possible

Osmolality A more representative measure of renal concentrating ability can be obtained Specific gravity depends on the number of particles present in a solution and the density of these particles Osmolality is affected only by the number of particles present Substances of interest are small molecules Sodium Chloride Urea

Osmole 1 g molecular weight of a substance divided by the number of particles into which it dissociates (= to MW of substance) Glu = 180 g/osm (C + H + O) NaCl = 58.5 g/osm (Na + Cl) The unit of measure used in the clinical laboratory is the milliosmole (mOsm)

Osmolarity Osmolality of a solution can be determined by measuring a property that is mathematically related to the number of particles in the solution Colligative property Changes in colligative properties Lower freezing point Higher boiling point Increased osmotic pressure Lower vapor pressure

Measuring Osmolality Measuring osmolality in the urinalysis laboratory requires an osmometer Additional step in the routine urinalysis procedure Automated osmometer utilizes freezing point depression to measure osmolality

Reagent Strip SG The reagent strip reaction is based on the change in pKa (dissociation constant) of a polyelectrolyte in an alkaline medium Releasing H ions in direct proportion to the number of ions in the solution The more hydrogen ions released, the lower is the pH Indicator bromothymol-LS blue on the reagent pad measures the change in pH Indicator changes from blue (1.000 [alkaline]), through shades of green, to yellow (1.030 [acid]) Not affected by nonionizing substances

Specific Gravity Dip Stick

Odor Not routinely reported Fresh urine: faintly aromatic Older urine: ammonia Metabolic disorders: maple syrup urine disease, ketosis (fruity), infection (ammonia/unpleasant) Food: garlic, onions, asparagus (genetic: only certain people can smell asparagus, but all produce odor)

Common Causes of Urine Odor Aromatic Normal Foul, ammonia-like Bacterial decomposition, urinary tract infection Fruity, sweet Ketones (diabetes mellitus, starvation, vomiting) Maple syrup Maple syrup urine disease Mousy Phenylketonuria Rancid Tyrosinemia Sweaty feet Isovaleric acidemia Cabbage Methionine malabsorption Bleach Contamination