Chapter03 (2) - Tagged
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Title
Urinalysis and Body Fluids, Seventh EditionAuthors: Susan King Strasinger, Marjorie Schaub Di Lorenzo
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Learning Outcomes
Upon completing this chapter, the reader will be able to:
List three major organic and three major inorganic chemical constituents of urine.
Describe a method for determining whether a fluid in question is urine.
Recognize normal and abnormal daily urine volumes.
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Learning Outcomes (continued)
Describe the characteristics of the specimen containers recommended for urine.
Describe the correct procedure for labeling urine specimens.
State four possible reasons why a laboratory would reject a urine specimen.
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Learning Outcomes (continued)
List changes in a urine specimen that remains at room temperature for more than 2 hours.
Discuss the actions of bacteria on unpreserved urine.
Discuss five methods for preserving urine specimens, including the advantages and disadvantages of each.
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Learning Outcomes (continued)
Instruct a patient on the correct procedure for collecting various specimen types (random, first morning, 24-hour timed, etc.).
Describe the type of specimen needed for optimal results in specific urinalysis procedures.
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History and Importance
Beginning of laboratory medicine:
Cavemen and Egyptians noted urine's color, turbidity, odor, volume, viscosity, sweetness.
5th century BC, Hippocrates wrote uroscopy book.
AD 1140 introduced color charts for urine.
1694: albuminuria determination by boiling.
Charlatans known as “pisse prophets” led to the first medical licensure laws.
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History and Importance Continued
17th century: invention of the microscope for evaluating sediment.
By 1827, urinalysis became part of routine physical exams:
Urine is readily available and easily collected.
It contains information that can assess metabolic functions via inexpensive tests.
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Definition and Reasons to Perform Urinalysis
CLSI defines urinalysis as testing urine with reliable and cost-effective procedures.
Reasons for urinalysis include:
Aiding disease diagnosis, screening for asymptomatic diseases, monitoring disease progression and therapy effectiveness.
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Urine Formation
Urine is formed as an ultrafiltrate of plasma.
Kidneys convert approximately 170,000 mL of filtered plasma, resulting in an average daily output of around 1200 mL.
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Urine Composition
Urine is composed of 95% water and 5% solutes.
Composition varies due to:
Diet, activity, metabolism, and endocrine functions.
Major organic solute is urea, accounting for half of dissolved solids.
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Urine Composition Continued
Inorganic solutes include: chloride, sodium, and potassium.
Urine may also contain cells, casts, crystals, mucus, and bacteria.
Increased levels may indicate disease.
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Urine Volume
Urine volume reflects the body’s hydration state.Influenced by:
Fluid intake, non-renal fluid loss, ADH variations, excretion of large dissolved solids.
Usual daily volume: 1200 to 1500 mL; normal range: 600 to 2000 mL.
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Urine Volume (continued)
Oliguria: decreased urine output—<1 mL/kg/h in infants, <0.5 mL/kg/h in children, <400 mL/day in adults.
Causes: vomiting, diarrhea, perspiration, severe burns.
Nocturia: increased urine output at night—normally 2-3 times more during the day.
Polyuria: >2.5 L/day in adults and >2.5 to 3 mL/kg/day in children.
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Polyuria in Diabetes Conditions
Diabetes Mellitus: increased volume due to excessive glucose excretion, leading to dilute urine with high specific gravity.
Diabetes Insipidus: results in decreased ADH production, leading to dilute urine with low specific gravity.
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Specimen Collection Guidelines
Use gloves when handling urine.
Containers should be clean, dry, leak-proof; ideally disposable with a wide mouth.
Recommended characteristics: clear containers capable of holding at least 50 mL; minimum of 12 mL for analysis.
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Specimen Collection Equipment
BD Vacutainer Urinalysis Transfer Straw and other specified collection kits.
Urine preservatives and their components are listed (e.g., Sodium Propionate).
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Specimen Labeling Requirements
Label should include:
Patient’s name, ID number, date, time, and possibly additional info such as age and healthcare provider's name.
Ensure label is placed on the container, not the lid.
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Specimen Labeling (continued)
Must accompany a requisition form (manual or computerized) containing matching information.
Include specifics such as type of specimen and any interfering medications.
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Specimen Rejection Reasons
Reasons specimens may be rejected:
Unlabeled specimens, urine in stool, incorrect container, wrong preservative, mismatched labeling.
Contaminated surfaces, insufficient quantity, improper transport.
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Specimen Rejection Continued
Labs should have written policies for rejecting specimens to maintain integrity and reliability.
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Specimen Handling Overview
Changes in urine composition occur both in vivo and in vitro.
Test specimens within 2 hours of collection or refrigerate for storage.
Bacterial growth can compromise results.
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Changes in Unpreserved Urine
Table 3-2 Changes in Unpreserved Urine
Color: modified/darkened due to oxidation.
Clarity: decreased due to bacterial growth.
Odor: increased from bacterial breakdown of urea.
pH: increased from urea breakdown.
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Changes in Unpreserved Urine (continued)
Glucose: decreased due to glycolysis.
Ketones: decreased due to volatilization.
Bilirubin: decreased due to light exposure.
Nitrite: increased due to bacterial multiplication.
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Specimen Preservation Techniques
Routine: refrigeration at 2°C to 8°C to limit bacterial growth.
Use of chemical preservatives that are bactericidal and useful during transport.
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Preservatives
Table 3-3 Urine Preservatives
Refrigeration: prevents bacterial growth but can precipitate phosphates; effective for 24 hours.
Boric acid: stabilizes pH but may interfere with drug analyses.
Formalin: excellent for sediment preservation but interferes with certain tests.
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Preservatives Continued
Sodium fluoride: good for drug analyses but affects reagent strip tests.
Commercial preservative tablets are convenient for transportation if refrigeration is not feasible.
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More on Preservatives
Light gray and gray C&S tube: stable for 48 hours at room temperature.
Yellow UA Plus tube: requires refrigeration within 2 hours and is instrument-compatible without preservatives.
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Continued on Preservatives
Cherry red/yellow Preservative Plus tube: remains stable for 72 hours at RT but sensitive to light.
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Preservatives Continued
Final notes on preservative options and their impacts on urine components.
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Urine Composition Variability
Composition of urine depends on:
Patient's metabolic state, collection timing, dietary intake, and medicinal use.
Specific instructions are critical for accurate collection.
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Random Specimen
Most common urinalysis specimen, can be collected at any time.
Suitable for routine screenings, but must record collection time.
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First Morning Specimen
Ideal for screening; collected immediately upon waking.
More concentrated than random specimens, used for various tests.
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Glucose Tolerance Specimens
Collect at the same intervals as corresponding blood samples, varying from fasting to 3, 4, or even 6-hour intervals.
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24-Hour (Timed) Specimen
Provides accurate quantitative results, requires strict hydration and collection protocols.
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24-Hour (Timed) Specimen (continued)
Must mix thoroughly before measurement and refrigerate during the collection.
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Common Errors in 24-Hour Specimen Collection
Loss of specimen, incorrect timing, inaccurate volume measurement, and transcription errors.
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Catheterized Specimens
Sterile specimens obtained via catheter for bacterial cultures.
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Midstream Clean-Catch Specimen
Safer option compared to catheterization.
Requires instruction for proper handling to minimize contamination.
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Midstream Clean-Catch Specimen (continued)
Instruction details for patients on how to collect a clean-catch sample to minimize contamination.
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Midstream Clean-Catch Specimen (continued)
Confirm correct labeling and handling of the specimen container after collection.
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Suprapubic Aspiration
Direct needle aspiration from bladder, ensuring no contamination for culture and cytology.
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Prostatitis Specimen
Requires collection across three containers for analysis of prostate health.
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Prostatitis Specimen (continued)
Specific testing for stem identification of conditions affecting the prostate versus the urinary tract.
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Pediatric Specimens
Use of hypoallergenic collection bags and proper instructions for collection from pediatric patients.
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Drug Specimen Collection
Emphasizes the importance of documentation and chain of custody from collection to lab receipt.
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Drug Specimen Collection (continued)
Considerations for ID verification and security, including witnessed versus unwitnessed collection.
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Drug Specimen Collection (continued)
Details on temperature checks and unusual color observations in drug testing specimens.