Urinalysis - Specimen Collection PDF 2024

Urinalysis - Specimen Collection Upon completion of the section, you will be able to discuss the components and procedures for selecting appropriate specimen types, collection methods and preservatives. Learning Objectives 1. State at least three clinical reasons for performing a routine urinalysi...

Urinalysis - Specimen Collection Upon completion of the section, you will be able to discuss the components and procedures for selecting appropriate specimen types, collection methods and preservatives. Learning Objectives 1. State at least three clinical reasons for performing a routine urinalysis 2. Describe three types of urine specimens and state at least one diagnostic use for each type 3. Explain the importance of accurate timing and complete collection of timed urine specimens 4. Describe the collection technique used to obtain the following specimens: a. Random void b. Midstream “clean catch” c. Catheterized d. Pediatric collection 5. Describe materials and procedures used for proper collection and identification of urine specimens 6. Identify five reasons for rejecting a urine specimen 7. State the changes possible in unpreserved urine and explain the mechanisms for each 8. Discuss urine preservatives, including their advantages, disadvantages, and uses 9. List and justify at least three tests that assist in determining whether a fluid is urine References: Strasinger, SK. Lorenzo, MS. Urinalysis and Body Fluids. 7th ed. Philadelphia, PA: F.A. Davis Company; 2021, pg 93-100 MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 1 of 6 Urinalysis - Specimen Collection Urine is a fluid biopsy of the kidney and provides great information. It is a non-invasive, readily available, easy to collect specimen to evaluate the kidney. The purposes of performing a routine urinalysis are: 1) To aid in the diagnosis of disease 2) To screen for asymptomatic, congenital or hereditary disease 3) To monitor disease progression 4) To monitor therapy effectiveness Urine Composition Affected by food and fluid intake, activity, medication, hormones, time of collection and contaminants; therefore, care must be given to ensure that the appropriate sample is ordered, collection techniques are closely followed and the specimens are handled correctly. Urine is normally 95% water and 5% solutes (majority urea, creatinine, uric acid, inorganic Cl, Na, & K). Urine Volume: Determined by body’s state of hydration Influenced by fluid intake, non-renal fluid loss, antidiuretic hormone (ADH) variations, excretion of large amounts of dissolved solids (e.g., glucose) Usual daily volume = 1200 to 1500 mL (RI = 600 to 2000 mL) Polyuria – volume > 2500 mL per 24 hrs o Diabetes mellitus (metabolic) – excretion of excess glucose with large amt of water (osmotic effect of glucose) o diabetes insipidus (renal) – ADH not secreted normally in response to ↓ blood vol, ↓ blood pressure, ↑ plasma osmolality and thirst. Kidney excretes lots of dilute urine. Oliguria – volume < 500 mL per 24 hrs o Dehydration, excess perspiration, renal disease, ↓blood to kidney Anuria – volume < 100 mL per 24 hrs o Renal failure, obstruction (calculi, enlarged prostate) Specimen Containers Single specimen collection The best container is clean, dry, disposable, and flat bottom. Usually, plastic is used It should have a wide mouth for ease of collection, a capacity of 50-100 mL and a tightly sealing lid A sterile disposable container is required for bacterial culturing If containers are reused, they must be clean and free of cleansing agents, which may interfere with chemical tests Time specimens Larger containers are required. Ideally those for 24-hour collections should have a capacity of 3L A wide mouth with a leak proof screw cap is essential Containers may be clear plastic, or opaque brown to preserve light sensitive substances such as bilirubin and urobilinogen Specimen Types MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 2 of 6 There are basically three types of urine specimens; random, first morning, and timed. 1. Random (spot) Specimen The most used specimen in the laboratory Collected at any time during daytime hours Easy and convenient to obtain Specimen is more dilute, therefore casts and cells are not as stable and some chemical constituents may not be detected Most affected by hydration, physical activity and diet of patient 2. First Morning Specimen Patient voids before going to bed and then a specimen is collected upon rising from the overnight sleep (8-hour specimen) Usually, the specimen of choice for routine screening The most concentrated Gives valuable information about the kidney’s ability to concentrate the glomerular filtrate Preserves formed elements such as casts and cells Deliver to laboratory within 2hrs or keep refrigerated. 3. Timed Specimen Because of normal fluctuations in excretion of specific substances (diurnal or circadian variation) some samples are collected over specified time periods. Specimens may also be collected during a specific time of day. Timed samples are required for quantitative analysis. Suitability of these specimens depends on strict adherence to the timing procedures. Example: 24-hour collections Eliminates the need to determine peak excretion Minimizes the effect of exercise, hydration, diet and metabolism on excretion of a substance Sample is useful for quantifying hormones, protein, evaluating glomerular filtration or renal reabsorption. The procedure for a 24-hour collection includes: 1. Giving clear written instructions for the patient 2. When starting the collection the first morning specimen is discarded 3. Recording the date and time of the start of collection 4. Saving all urine voided after the first discarded sample in a suitably large container and properly preserved. Store in refrigerator during collection period. 5. Collecting the first morning specimen at the end of the 24-hour period and adding it to the container 6. Recording the date and time of completion 7. Total compliance by the patient is necessary 8. Once specimen has been sent to the lab: MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 3 of 6  Mix well and total volume is accurately measured with graduated cylinder and recorded If more than one container, pool containers in bucket and measure total volume A sufficient aliquot must be poured off and saved for testing. Aliquot may be poured off for urinalysis as well. Possible errors:  addition of urine formed before the start of collection period will falsely elevate results  failure to include urine produced at the end of the collection period will falsely decrease results. Collection Techniques Routine Void A routine voided urine specimen requires no patient preparation and is collected by having the patient urinate into an appropriate container. Midstream Clean-Catch method The most common approach for collecting first-morning or random samples is the midstream clean catch method. The midstream clean catch sample minimizes vaginal and urethral contamination. This sample is also suitable for bacterial culture if collected in a sterile container. This procedure requires additional preparedness. The patient is given cleansing towelettes and specific instructions for washing and collecting. The procedure includes: 1. Thorough cleansing of the urethra of the female or the urethral opening 2. Collect midstream urine by a. passing some urine into the toilet b. interrupting the stream c. then collecting a portion into the container 3. The last portion of the urine stream is passed into the toilet  To prevent contamination of the specimen and container, the interior of the container must not come in contact with the patient’s hand or the urethral area of the body. Catheterized Specimen Urine is withdrawn under sterile conditions with a sterile flexible tube inserted through the urethra into the bladder. A bacterial culture is the most requested test on a catheter specimen. Pediatric Specimen An alternative to catheterization in very young patients is the use of disposable sterile plastic bags. After the urethra is cleansed, the bag is attached by its adhesive backing. The bag is checked often to ensure adequate urine has been collected. The bag is removed, labelled and sent to the laboratory. Alternatively, transfer specimen into sterile container, label, and send to the lab. MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 4 of 6 Labeling All containers must be labelled immediately upon collection The patient identification information must be on the container, NOT the lid. The labels must adhere during refrigeration or if the container becomes wet For safety, labels indicating chemical preservatives that have been added are required. Preservatives Ideally, urine specimens should be analyzed within 2 hours. If it cannot be analyzed within 2 hours, i.e. requires transportation or if the specimen is a collection over a period, preservation is required. The methods of preservation must not interfere with the testing procedure or alter constituents. The following characteristics may change in unpreserved urine: Physical properties – color, odor, clarity Chemical properties – pH, glucose, ketones, bilirubin, urobilinogen and nitrates Microscopic properties – RBCs, WBCs, casts and bacteria Refrigeration The best preservation is refrigeration at 4°C because it does not interfere with any chemical tests or physical properties; it preserves microscopic elements and inhibits bacterial growth. Because some screening tests are temperature sensitive, the specimen should return to room temperature before testing. If a lengthy period of transportation or delay in testing is required, the specimen may be frozen, however microscopic elements will be destroyed. One disadvantage of refrigeration is the tendency for crystals to come out of solution and precipitate, changing the clarity of the specimen and adding formed elements to the microscopic report Formaldehyde Formaldehyde is excellent for preserving formed elements for microscopic analysis; however, it interferes with glucose, blood, and leukocyte esterase. Sodium fluoride Sodium fluoride preserves glucose by inhibiting glycolysis. It is the ingredient in commercial preservative tablets used when refrigeration is not possible. Acidification Acids may be added to 24-hour specimen containers to keep certain solutes in solution and prevents bacterial growth & metabolism. Commonly used acids include hydrochloric acid (for Ca2+, Mg 2+ & PO4-), boric acid (for hormones and proteins) and acetic acid (for hormones). Care is required by the patient and laboratory personnel when handling these containers. Written instructions may be given to the patient. Potential changes in unpreserved urine at room temperature for longer than 2 hours MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 5 of 6  Physical Changes Color Due to oxidation/reduction i.e. bilirubin to biliverdin, urobilinogen to urobilin Clarity Decreases – bacterial proliferation, crystal precipitation Odor Increased ammonia – breakdown of urea by bacteria on standing Chemical Changes pH Increase – bacterial decomposition of urea to ammonia Glucose Decrease – cellular or bacterial glycolysis Ketones Decrease – bacterial metabolism of acetoacetate to acetone Bilirubin Decrease – photo oxidation of bilirubin to biliverdin Urobilinogen Decrease – oxidation urobilinogen to urobilin Nitrite Increase – bacterial production following specimen collection Microscopic Changes RBC, WBC, and Casts Decrease – disintegration of cellular & formed elements, esp. in dilute alkaline urine Bacteria Increase – bacterial proliferation following specimen collection Trichomonas Decreased – loss of motility, death. Rejecting a Specimen include: Unlabeled urine specimen container Mislabelled urine specimen container o Label on container and requisition don’t match Poor collection technique – ie. contaminants Wrong specimen type for test requested Not properly preserved Insufficient volume Is the Fluid Urine? Example - labs that perform urine testing for illicit drugs. A fluid is urine if it has: o pH 4.0 – 8.0 o Specific gravity 1.002 – 1.035 o Temperature 32.5 – 37.5°C immediately following collection o Creatinine [c] ~ 50 times that of plasma o Glucose and protein should be negative MLSC 2325, Fall 2024, Prepared by Nancy Tam Page 6 of 6