MN

Urine Collection and Specimens (Introduction through Chapter 6)

Urine: overview and clinical relevance

  • Urine is an ultrafiltrate of plasma and is used to evaluate and monitor homeostasis and metabolic disease processes. It contains solutes that have been either reabsorbed or excreted, including electrolytes, glucose, protein, and other substances. The composition depends on the person’s activity, health, diseases, and diet; urine volume also varies.
  • Urine as a noninvasive, fluid biopsy of the kidney provides information about kidney status and disease processes.
  • Reasons to study urine:
    • Aid in diagnosis (e.g., urinary tract infections, diabetes, pregnancy).
    • Screen for asymptomatic diseases (e.g., metabolic diseases, Buerger's disease, pregnancy).
    • Monitor disease progression (e.g., chronic diabetes).
    • Monitor effectiveness of therapy and potential therapy-related complications.
  • Practical aspects:
    • Urine is easily collected and readily available.
    • Tests are typically inexpensive and accurate.
  • Key concepts:
    • Urine reflects a snapshot of renal function and systemic metabolism; changes in solute concentrations can indicate pathology or physiologic variation.
    • Environmental and behavioral factors (activity level, hydration, timing of meals, exercise) influence urine composition.

Types of urine specimens

  • Three main types:
    • First morning specimen: collected right after waking; urine has been in the bladder about 8\,\text{hours}.
    • Random (spot) specimen: collected at any time during the day.
    • Timed specimen: collected over a defined period (e.g., 24\,\text{hours}) or at specified times.
  • First morning specimen details:
    • Often tested for nitrates (bacteria breakdown product), protein; can assess red blood cells (RBC), white blood cells (WBC), and casts; cytology studies are favored due to a larger number of epithelial cells in this concentrated sample.
  • Random specimen details:
    • Most common type; used for routine screening; convenient but may not reflect the patient’s typical status as accurately as timed collections.
    • Can be used for cytology.
  • Timed collections details:
    • Two main forms:
    • Time-period collections: 2\,\text{hour}, 12\,\text{hour}, or 24\,\text{hour} collections.
    • Specified-time collections: samples collected at particular times (e.g., 6\,\text{AM} or 2\,\text{hours after}\, \text{medication}).
    • Circadian and diurnal variations can affect excretion; timed collections help capture evidence across variation.
    • Why collect timed samples: to ensure you capture evidence across the variation in excretion and to standardize collection for comparison.
  • Types of timed collection instructions:
    • Start by voiding completely and discarding that urine.
    • Note the start date and time.
    • Collect all urine produced during the specified time frame.
    • At the end of the period, void again and collect that final portion (and discard if applicable per protocol).
    • Record end date and time, label, and refrigerate during collection.
    • Bring the refrigerated specimen to the lab for analysis.
  • Other specimen types:
    • Fasting specimens: urine collected after a defined fasting period.
    • 2‑hour postprandial specimens: collected 2\,\text{hours} after a meal to monitor glucose and insulin therapy.
    • Glucose tolerance specimens: urine collected after glucose ingestion; typically paired with a blood glucose test to assess metabolic response.

Urine collection techniques (outline of techniques studied)

  • Routine void (routine urinalysis):
    • Also called routine void; collected for screening or monitoring without special preparation.
    • Can be first morning or random; suitable for monitoring conditions like diabetes (glucose and protein in urine).
    • Not ideal for detecting infection (urine may be contaminated less with a clean catch; see clean catch below).
  • Midstream (clean catch) collection:
    • Most ideal for bacterial culture to detect urinary tract infections or kidney infections; reduces skin contamination and epithelial cells.
    • Uses for routine urinalysis and cytology as well.
    • Procedure/instructions:
    • Wash hands with soap and water to reduce hand bacteria contamination.
    • Open a sterile urine container without contaminating its interior.
    • Cleanse the genital area with a mild antiseptic towelette (provided); discard towelette.
    • Begin urinating into the toilet; after a few seconds, insert the collection container to collect the midstream portion.
    • Collect until the container is at least half full, then finish urinating into the toilet.
    • Screw the lid on tightly, wash hands, label the container, and deliver to the lab promptly.
  • Catheterized specimen:
    • Performed by a physician or nurse; sterile collection under sterile conditions; reduces skin contamination and helps determine which kidney is involved when needed.
    • Indicated when patient cannot void or when precise sampling is required.
    • Types of catheters:
    • Straight catheter: inserted to collect urine then removed.
    • Indwelling (Foley) catheter: remains in place to collect urine over time.
    • Procedure context: clean the area, insert sterile catheter through the urethra into the bladder; urine flows into collection container; ensure catheter is removed if a straight catheter was used.
  • Suprapubic aspiration:
    • Urine collection through the abdominal wall directly from the bladder.
    • Mostly used in infants; eliminates contamination risk.
    • Indicated for anaerobic bacterial cultures and when other methods are not feasible.
    • Performed by trained physicians; obstrewn limitations for laboratory personnel to perform.
    • Procedure: cleanse abdomen, puncture the abdominal wall, access the bladder with a needle/syringe to collect urine; collect into sterile container; ensure needle is removed and container is properly labeled.
  • Pediatric collections:
    • Challenges include limited cooperation; techniques include:
    • PD bag method (perineal area dressed with a PD bag attached around the penis or around the vagina using a skin adhesive); monitor every ~15\,\text{min} to ensure adequate volume; transfer to a leak-proof container and label.
    • Hats for diapered or non-toilet-trained children for routine urinalysis (less ideal for cultures due to contamination).
  • Drug specimen collection and chain of custody:
    • Requires extensive documentation to ensure legal admissibility; proper patient identification and chain-of-custody by which personnel handled the specimen.
    • Collection can be observed or unobserved; observed collection provides higher assurance that the sample is urine from the patient.
    • If urine identity is suspicious, a creatinine test may be used to confirm that the sample is urine (creatinine level test).

Handling, storage, and timing of urine specimens

  • Timeliness is critical:
    • Ideally, urine should be tested within 2\,\text{hours} of collection.
    • If testing cannot occur within 2\,\text{hours}, refrigerate the specimen during transport and storage.
  • Why timing matters:
    • Bacteria can grow if urine is left at room temperature, altering color, clarity, solutes, and chemical composition (e.g., glucose decreases as bacteria metabolize it).
  • Preservatives if refrigeration is unavailable:
    • Hydrochloric acid (HCl) is used as a preservative when refrigeration is not possible.
  • Practical notes:
    • When performing chemical and microscopic urinalysis, refrigeration helps maintain sample integrity and reduces alterations due to bacterial growth.

Key terms and concepts to remember

  • Nitrates: breakdown product of bacteria; their presence in urine can indicate bacterial infection in the urinary tract.
  • Epithelial cells: higher numbers in first morning samples can reflect shedding; in clean catch, fewer epithelial cells indicate a cleaner sample.
  • Casts: structures formed in the kidney tubules; more stable in concentrated samples like the first morning specimen.
  • Diurnal and circadian variations: natural fluctuations in urine composition over the day; important for timed collections.
  • Creatinine: a waste product used to verify that a urine sample is indeed urine, especially in drug testing or questionable samples.

Summary: practical workflow and implications

  • Urine analysis is a versatile, noninvasive tool for diagnosing, screening, and monitoring kidney function and systemic metabolic processes.
  • Choose the specimen type based on the clinical question: routine screening vs. infection culture vs. metabolic monitoring.
  • Follow meticulous collection procedures to minimize contamination (especially for bacterial cultures) and ensure sample integrity (timing, handling, labeling).
  • When collecting timed specimens, carefully coordinate start and end times, document dates and times, and ensure proper refrigeration during collection.
  • In drug testing and chain-of-custody scenarios, emphasize documentation and sample integrity; use confirmatory tests (e.g., creatinine) if needed.
  • Be mindful of practical considerations for special populations (pediatric, elderly, catheterized patients) and adjust collection methods accordingly while maintaining sterile technique and patient safety.

Formulas and time references (LaTeX)

  • First morning urine collection duration: \approx 8\text{ hours} in bladder prior to collection.
  • Timed-collection durations:
    • 24\text{ hours}
    • 12\text{ hours}
    • 2\text{ hours} after events (meals/medications)
  • Observational timing examples:
    • Start at \text{noon}; end at the following \text{noon} for a 24-hour collection.
  • Storage time requirement: urine should be tested within 2\text{ hours} or refrigerated.
  • Pediatric collection monitoring interval: every 15\text{ minutes} during PD bag collection.