Urine Specimen Types, Collection, and Preservation Study and Preservation Notes
Purposes and Diagnostic Significance of Routine Urine Analysis (UA)
Purposes of Routine Urine Analysis:
To aid in the diagnosis of various diseases.
To screen for diseases that are asymptomatic, congenital, or hereditary.
To monitor the progression of a disease.
To monitor the effectiveness of a therapy or identify potential complications.
Why Study Urine?
Urine analysis (UA) is considered a "fluid biopsy" of the kidney.
It provides a noninvasive means to evaluate the kidney and its functions.
Specimens are usually readily available from the patient.
Urine is an ultra-filtrate of plasma, making it a valuable tool to evaluate and monitor body homeostasis and numerous metabolic diseases.
Urine Specimen Types and Collection Methodologies
Routine Void:
Requires no specific patient preparation.
First Morning Specimen:
The patient must empty their bladder at night before going to bed.
The specimen is collected first thing in the morning.
This is the most concentrated specimen and is often the preferred specimen for testing.
Random Specimen:
Used for routine screening.
Results can be affected by excess fluid intake or physical exercise.
Timed Specimens:
Collections occurring for a predetermined length of time.
Collections performed at a specified time of day.
Specialized Collection Techniques
Midstream "Clean Catch":
Primary use: For bacterial cultures or to prevent vaginal contamination.
Requires specific cleaning supplies and detailed instructions to the patient.
A sterile container may be required.
Procedural steps:
Thoroughly clean and rinse the glans penis or urethral meatus before beginning the collection.
The patient begins urination into the toilet.
The midstream portion is collected in the specimen container.
The patient finishes voiding into the toilet.
Catheterized Specimens:
A sterile specimen collected directly from the bladder using a hollow tube called a catheter.
The most common test performed on these specimens is a bacterial culture.
Suprapubic Aspiration:
Allows for a specimen completely free of contamination, used for culture and cytology.
Involves the external introduction of a needle into the bladder for aspiration.
Often utilized as a pediatric specimen collection method.
Pediatric Specimens:
Soft, clear, plastic bags featuring hypoallergenic tape are applied to the genital area.
A clean-catch method using a sterile bag can be implemented for microbiology specimens.
Bags equipped with tubes leading to a larger container are available for timed specimen collections.
The 24-Hour Timed Urine Collection
Purpose: Tests for specific chemicals and hormones by collecting all urine voided in a continuous window.
Protocol and Timing:
The process usually begins in the morning and ends the following morning.
Collection starts after discarding the first morning urine of day one; this exact time is noted.
The collection ends at that same exact time the next morning.
Procedure: After the resident/patient voids, their individual container is emptied into the large specimen container.
Critical Requirements:
If any urine is discarded or improperly collected, the entire collection process must restart from the beginning.
The specimen label must be placed on the container itself, not on the lid.
The label should include name, room number, dates, and times of collection.
The container may be stored on ice to maintain the temperature of the specimen.
Specimen Rejection and Integrity
Reasons for Specimen Rejection:
Unlabeled or mislabeled specimens.
A mismatch between the specimen name or identification (ID) number and the order slip.
The collection technique was inappropriate for the specific test ordered.
The specimen was not properly preserved or there was a significant time delay in receipt at the lab.
The sample is visibly contaminated.
Insufficient volume was provided for the tests ordered.
Changes in Unpreserved Urine:
Changes result from bacterial growth, solute precipitation, or the alteration of urine solutes into a different form.
Expected physical and chemical changes include:
Decreased urine clarity and increased odor.
Possible color changes due to solute alteration.
False-negative glucose results.
Increased nitrite levels and increased pH.
Disintegration of formed elements.
Handling and Preservation Methods
Preservation Guidelines:
Proper techniques are required to preserve specimen integrity if testing is delayed by or more.
Preservative choice depends on the type of collection, tests to be performed, and the time delay before testing.
Refrigeration is the most common technique but should not be used for routine testing if analysis occurs within .
Preservative Characteristics:
Refrigeration:
Advantages: Does not interfere with chemical tests; preserves glucose and sediments well.
Disadvantages: Raises specific gravity when measured by hydrometer; precipitates amorphous phosphates and urates.
Additional Info: Prevents bacterial growth for .
Thymol:
Advantages: Preserves protein and formed elements well.
Disadvantages: Interferes with acid precipitation tests for protein.
Boric Acid:
Advantages: Does not interfere with routine analyses except for pH.
Disadvantages: May precipitate crystals if used in large amounts.
Additional Info: Keeps pH at approximately ; is bacteriostatic at (can be used for culture transport).
Formalin (Formaldehyde):
Advantages: Excellent preservative for sediment.
Disadvantages: Acts as a reducing agent; interferes with chemical tests for glucose, blood, leukocyte esterase, and copper reduction.
Additional Info: Rinse container with formalin to preserve cells and casts.
Toluene:
Advantages: Does not interfere with routine tests.
Disadvantages: Floats on the surface and clings to pipettes and testing materials.
Sodium Fluoride:
Advantages: Prevents glycolysis and is good for drug analyses.
Disadvantages: Inhibits reagent strip tests for glucose, blood, and leukocytes.
Additional Info: Sodium benzoate may be used instead for reagent strip testing.
Phenol:
Advantages: Does not interfere with routine tests.
Disadvantages: Causes a change in odor.
Additional Info: Use 1 drop per ounce of specimen.
Commercial Preservative Tablets:
Advantages: Convenient for when refrigeration is not possible; controlled concentrations minimize interference.
Disadvantages: Tablet composition must be checked for effects on specific tests.
Commercial Kits (e.g., Becton Dickinson):
Gray C&S tube: Contains boric acid; sample stable at room temperature (RT) for ; preserves bacteria. Do not use for UA.
Yellow plain UA tube: Used on automated instruments; round or conical bottom.
Cherry red/yellow top tube: Contains sodium propionate; stable for at RT; conical bottom.
Saccomanno Fixative: Used specifically for cytology studies to preserve cellular elements.
Urine Culture and Sensitivity (C&S) and MCS Testing
Definitions:
Culture: Determining if bacteria are growing.
Sensitivity: Determining which antibiotics are effective against the bacteria.
Testing Parameters:
Readings are taken after , , and .
Specimen source: Midstream urine or sterile catheter specimen (never collect from a catheter bag).
MCS Result Classifications:
Sensitive (S)
Intermediate (I)
Resistant (R)
Materials:
Blood Agar
CLED Agar
Clinical Identification: Is the Fluid Urine?
Verification: Often required in drug screenings or for specimens collected by needle aspiration.
Chemical Markers:
Creatinine concentration in urine is higher than in plasma.
Urea, sodium (Na), and chloride (Cl) levels are significantly higher in urine than in other body fluids.
Physiologic Ranges for Urine:
Specific Gravity: to
pH: to
Analyte Presence:
Urine from healthy individuals contains no protein or glucose, unlike many other body fluids.
Purposes of Routine Urine Analysis:
To aid in the diagnosis of various diseases, including renal disorders, urinary tract infections, and metabolic diseases.
To screen for diseases that are asymptomatic, congenital, or hereditary, thus enabling early intervention.
To monitor the progression of a disease, such as diabetes or chronic kidney disease, by assessing changes in urine composition over time.
To monitor the effectiveness of a therapy or identify potential complications; for example, checking protein levels in nephrotic syndrome patients following steroid treatment.
Why Study Urine?
Urine analysis (UA) is considered a "fluid biopsy" of the kidney, providing insight into kidney function.
It provides a noninvasive means to evaluate the kidney and its functions without the need for invasive procedures.
Specimens are usually readily available from the patient, ensuring that samples can be collected quickly in various clinical settings.
Urine is an ultra-filtrate of plasma, making it a valuable tool to evaluate and monitor body homeostasis and numerous metabolic diseases, as it reflects changes in hydration status, electrolyte imbalances, and metabolic byproducts.
Urine Specimen Types and Collection Methodologies
Routine Void:
Requires no specific patient preparation, making it the most convenient type for general screening.
First Morning Specimen:
The patient must empty their bladder at night before going to bed.
The specimen is collected first thing in the morning when the urine is most concentrated, often preferred for tests such as pregnancy tests and proteinuria assessments.
Random Specimen:
Used for routine screening where timing is not crucial; however, results can be affected by excess fluid intake or physical exercise which may dilute or alter the composition of the urine.
Timed Specimens:
Collections occurring for a predetermined length of time, such as 24-hour collections, are essential for assessing kidney function and quantifying substances like creatinine or protein.
Collections performed at a specified time of day can provide targeted information on specific biological processes.
Specialized Collection Techniques
Midstream "Clean Catch":
Primary use: For bacterial cultures or to prevent vaginal contamination, thus increasing the accuracy of test results.
Requires specific cleaning supplies and detailed instructions to ensure the sample remains uncontaminated.
Procedural steps include thorough cleansing of the genital area, initiating urination into the toilet, and collecting the midstream portion in a sterile container, which reduces the chance of external contaminant presence.
Catheterized Specimens:
A sterile specimen collected directly from the bladder using a hollow tube called a catheter, ideal for patients who are unable to independently void their bladder.
The most common test performed on these specimens is a bacterial culture, as it provides direct access to urine in the bladder, minimizing contamination.
Suprapubic Aspiration:
Allows for a specimen completely free of contamination, critically important for accurate culture and cytological analysis.
Involves the external introduction of a needle into the bladder for aspiration, which is an invasive procedure typically used when other methods are impractical, often utilized as a pediatric specimen collection method.
Pediatric Specimens:
Soft, clear, plastic bags featuring hypoallergenic tape are applied to the genital area, designed to capture urine in infants and young children.
A clean-catch method using a sterile bag can be implemented for microbiology specimens, providing a non-invasive alternative for accurate results.
Special bags equipped with tubes leading to a larger container are available for timed specimen collections, ensuring precise volume measurements and reducing contamination risks.
The 24-Hour Timed Urine Collection
Purpose: Tests for specific chemicals and hormones by collecting all urine voided in a continuous window, crucial for conditions requiring precise quantification of metabolic substances.
Protocol and Timing:
The process usually begins in the morning and ends the following morning, enabling accurate tracking of physiological output over a full day.
Collection starts after discarding the first morning urine of day one; this exact time is noted to ensure accurate tracking of the collection period.
The collection ends at that same exact time the next morning, ensuring all urine produced in the specified time frame is captured.
Procedure: After the resident/patient voids, their individual container is emptied into the large specimen container, making it crucial to maintain the integrity of the sampling throughout the duration.
Critical Requirements:
If any urine is discarded or improperly collected, the entire collection process must restart from the beginning, emphasizing the importance of diligence in sample collection.
The specimen label must be placed on the container itself, not on the lid to avoid mislabeling.
The label should include name, room number, dates, and times of collection for clear identification and tracking.
The container may be stored on ice to maintain the temperature of the specimen and prevent metabolic changes that could alter test results.
Specimen Rejection and Integrity
Reasons for Specimen Rejection:
Unlabeled or mislabeled specimens significantly hinder testing processes.
A mismatch between the specimen name or identification (ID) number and the order slip can lead to diagnostic errors.
The collection technique was inappropriate for the specific test ordered, affecting the validity of the results.
The specimen was not properly preserved or there was a significant time delay in receipt at the lab, which can alter the chemical composition.
The sample is visibly contaminated, which compromises the test results.
Insufficient volume was provided for the tests ordered, leading to the inability to perform necessary analysis.
Changes in Unpreserved Urine:
Changes that occur result from bacterial growth, solute precipitation, or the alteration of urine solutes into a different form, impacting the reliability of results.
Expected physical and chemical changes include:
Decreased urine clarity and increased odor due to bacterial activity.
Possible color changes due to solute alteration, which can lead to misinterpretation of results.
False-negative glucose results often observed if the sample is left at room temperature for an extended period.
Increased nitrite levels and increased pH can signal infection or other underlying conditions.
Disintegration of formed elements may occur, leading to the loss of important diagnostic information.
Handling and Preservation Methods
Preservation Guidelines:
Proper techniques are required to preserve specimen integrity if testing is delayed by or more, ensuring that results remain accurate and reliable.
Preservative choice depends on the type of collection, tests to be performed, and the time delay before testing, requiring the laboratory staff to be knowledgeable about these factors.
Refrigeration is the most common technique but should not be used for routine testing if analysis occurs within as it may impact some tests.
Preservative Characteristics:
Refrigeration:
Advantages: Does not interfere with chemical tests; preserves glucose and sediments well, making it a standard practice for short-term storage.
Disadvantages: Raises specific gravity when measured by hydrometer; precipitates amorphous phosphates and urates, potentially affecting certain assays.
Additional Info: Prevents bacterial growth for , extending the time window for testing viability.
Thymol:
Advantages: Preserves protein and formed elements well, allowing accurate results for protein-related tests.
Disadvantages: Interferes with acid precipitation tests for protein, which can lead to misleading outcomes.
Boric Acid:
Advantages: Does not interfere with routine analyses except for pH, maintaining versatility in many testing scenarios.
Disadvantages: May precipitate crystals if used in large amounts, thus limiting its use in high-concentration scenarios.
Additional Info: Keeps pH at approximately ; is bacteriostatic at , making it suitable for culture transport when necessary.
Formalin (Formaldehyde):
Advantages: Excellent preservative for sediment, preserving cellular and particulate elements effectively.
Disadvantages: Acts as a reducing agent; interferes with chemical tests for glucose, blood, leukocyte esterase, and copper reduction, which can lead to test inaccuracies.
Additional Info: Rinse container with formalin to preserve cells and casts prior to sampling.
Toluene:
Advantages: Does not interfere with routine tests, ensuring reliability across various analyses.
Disadvantages: Floats on the surface and clings to pipettes and testing materials, complicating the test procedure and requiring careful handling.
Sodium Fluoride:
Advantages: Prevents glycolysis and is excellent for drug analyses, particularly useful in toxicology assessments.
Disadvantages: Inhibits reagent strip tests for glucose, blood, and leukocytes, thus requiring alternative testing methods in some cases.
Additional Info: Sodium benzoate may be used instead for reagent strip testing when necessary.
Phenol:
Advantages: Does not interfere with routine tests, maintaining accuracy across various assays.
Disadvantages: Causes a change in odor, which may lead to concerns over sample integrity.
Additional Info: Use 1 drop per ounce of specimen to ensure proper preservation levels.
Commercial Preservative Tablets:
Advantages: Convenient for when refrigeration is not possible; controlled concentrations minimize interference, facilitating usage in varying environments.
Disadvantages: Tablet composition must be checked for effects on specific tests to avoid erroneous outcomes.
Commercial Kits (e.g., Becton Dickinson):
Gray C&S tube: Contains boric acid; sample stable at room temperature (RT) for ; preserves bacteria. Do not use for UA due to potential interferences.
Yellow plain UA tube: Used on automated instruments; designed with a round or conical bottom for efficient processing.
Cherry red/yellow top tube: Contains sodium propionate; stable for at RT; designed with a conical bottom to facilitate sample collection.
Saccomanno Fixative: Used specifically for cytology studies to preserve cellular elements, ensuring accurate analysis of cellular morphology and patterns.
Urine Culture and Sensitivity (C&S) and MCS Testing
Definitions:
Culture: Determining if bacteria are growing, essential for diagnosing infections and guiding treatment.
Sensitivity: Determining which antibiotics are effective against the bacteria, assisting in tailored therapeutic approaches.
Testing Parameters:
Readings are taken after , , and , allowing adequate time for bacterial growth and antibiotic response.
Specimen source: Midstream urine or sterile catheter specimen (never collect from a catheter bag), ensuring samples are uncontaminated and representative of the urinary tract.
MCS Result Classifications:
Sensitive (S): Indicates that the bacteria are likely to be inhibited by the antibiotic.
Intermediate (I): Suggests potential effectiveness, but could vary based on drug concentration in the body.
Resistant (R): Indicates that the bacteria are likely to survive despite the antibiotic treatment, necessitating alternative therapies.
Materials:
Blood Agar: A rich medium that supports the growth of many bacteria, useful for detecting hemolytic properties.
CLED Agar: A culture medium that enables identification of certain pathogens while preventing swarming of Proteus species., thereby enhancing diagnostic accuracy.
Clinical Identification: Is the Fluid Urine?
Verification: Often required in drug screenings or for specimens collected by needle aspiration to confirm sample integrity and validity.
Chemical Markers:
Creatinine concentration in urine is higher than in plasma, serving as a key indicator of kidney function.
Urea, sodium (Na), and chloride (Cl) levels are significantly higher in urine than in other body fluids, cementing its role as a principal means of metabolic waste elimination.
Physiologic Ranges for Urine:
Specific Gravity: to , an important measure of urine concentration and hydration status.
pH: to , indicative of metabolic processes and dietary influences on urine composition.
Analyte Presence:
Urine from healthy individuals contains no protein or glucose, unlike many other body fluids, which aids in differentiating between normal and pathological states.