1. Urinalysis
Urinalysis Overview
Urinalysis is a widely used screening test.
It provides valuable information quickly and economically.
The analysis includes physical, chemical, and microscopic evaluation of urine.
A test strip is utilized which is dipped in a urine specimen (straight void or mid-stream).
A color reaction occurs on these "pads" and is then observed or read by an analyzer.
Purposes of Urinalysis
Aids in the diagnosis of diseases.
Screens populations for asymptomatic, congenital, or hereditary diseases.
Monitors the progress of diseases.
Assesses effectiveness or complications of therapy.
Conducted for various reasons including routine health checks.
Preanalytical Stage of Urinalysis
Initiated by a doctor’s request for urinalysis.
Collection of the specimen can be MSU (mid-stream urine) or voided urine, depending on patient's age.
The specimen must be properly labeled with patient’s name and identifier, and the date and time of collection.
Proper transportation to the lab is crucial.
The specimen is treated as infectious and must be handled according to standard precautions.
Patients are instructed to wash hands before collection and to avoid touching the inside of containers to prevent contamination.
Errors during this preanalytical phase can significantly affect results.
Types of Urine Samples
Routine Urinalysis
Specimen should be collected in a clean, dry container.
First morning specimen is preferred due to higher concentration of analytes.
Ideally examined within two hours for optimal evaluation.
Random Urine
Most common type of sample, collected at any time.
May result in dilution and lower analyte levels, potentially skewing health assessments.
First Morning Urine
Preferred for analysis and microscopic exam.
Typically more concentrated due to overnight bladder retention.
Higher levels of cellular elements and analytes such as glucose and protein are present.
Midstream Clean Catch Urine
Best for culture and sensitivity testing, reduces cellular and microbial contamination.
Patients must clean the urethral area, void the initial portion into the toilet, collect midstream in a container, and finish voiding into the toilet.
24-Hour or Timed Specimens
Necessary for measuring substances like creatinine, urea, glucose, etc., affected by diurnal variations.
The bladder must be emptied before the collection starts, subsequent urine is collected for 24 hours.
Requires refrigeration during the collection period.
Catheter Collection Specimen
Conducted for patients unable to urinate on their own; involves inserting a Foley catheter through the urethra.
Suprapubic Aspiration Specimen
Method used for bedridden patients requiring sterile specimens; urine is collected via needle aspiration through the abdominal wall into the bladder.
Pediatric Specimen
Special collection bag adhered to skin for infants and small children.
Urine is later poured into a collection cup or transferred back into an evacuated tube.
Urine Containers
Containers for urine collection must be clean, dry, and free from contaminants.
Reusing containers is inadvisable; disposable, inert plastic containers with leak-proof lids are standard.
Urine Volume
Minimum volume for routine analysis is around 12 mL, 50 mL preferred.
12 mL is necessary for testing and concentration ratios (12:1).
Allows standardized assessment of physical properties, while smaller volumes may be used for children and renal patients.
Preservatives in Urine Collection
Urine samples should be analyzed within two hours.
Delayed analysis can result in changes due to bacterial activity, such as ammonia production and pH increase.
If analysis within two hours is not possible, preservatives may be utilized (HCl, boric acid, acetic acid, toluene, formaldehyde, thymol).
Preservation duration varies: 24-72 hours.
Physical Properties of Urine
Properties Assessed
Volume, color, clarity, odor (occasionally).
Volume is typically noted during 24-hour tests.
Urine Volume
Normal 24-hour urine volumes: 1200-1500 mL, may range from 600-1600 mL.
Water intake and urine volumes have a direct relationship.
Urine Color
Influenced by pigments:
Urochrome (primary yellow pigment).
Uroerythrin (red pigment).
Urobilin (orange-yellow pigment).
Normal urine colors range from pale yellow to amber; variations indicate concentration levels (light suggests dilution, darker indicates concentration).
Urine Clarity
Urine is expected to be clear when voided.
Cloudiness may indicate abnormality; classifications include clear, slightly cloudy, cloudy, turbid.
Cloudiness can result from sediments, crystals, bacteria, mucous, or cellular components like WBCs and RBCs.
Urine Odor
Urine typically has a faintly aromatic scent.
Standing urine acquires a strong ammonia odor due to bacterial action on urea.
Specific Gravity
A measure indicating concentration of dissolved substances in urine.
Normal range: 1.003 to 1.035.
Specific gravity is important for evaluating kidney function and hydration status.
Higher specific gravity indicates concentrated urine; lower specific gravity reflects diluted urine often due to high water intake.
Specific Gravity Measurement: can be assessed via Multistix or refractometer (a tool measuring solute concentration through refractive index).
Osmolality
Another method of measuring kidney's concentrating ability.
Typically ranges between 500-800 mOsm/kg; in cases of renal failure, can be around 285 mOsm/kg.
Assesses both kidney function and hydration.
More complex and costly than specific gravity; thus, less commonly performed.
Chemical Tests in Routine Urinalysis
Reagent Strip Tests
Utilizes multiple dry reagent strips for urinalysis methods.
Strips are impregnated with chemicals that react upon contact with urine, indicated by color changes.
Analyzer processes the color change to quantify analyte levels.
Advantages of Dry Multi Sticks
Offer rapid results, cost-effectiveness, stability, and ease of use.
Require appropriate conservation and handling to avoid errors.
pH Measurement
Kidney regulates extracellular fluid acidity; normal blood pH: 7.4.
Urinalysis shows average pH of 4.6 to 8.
Methyl red and bromothymol blue used as indicators.
Fresh samples are necessary to avoid falsely alkaline pH results.
Protein Testing
Used for renal disease detection (proteinuria); fundamental abnormal finding in urinalysis.
Conditions causing proteinuria include glomerular and tubular damage, prerenal disorders, and urinary tract disorders.
Presence of casts distinguish upper urinary tract from lower urinary tract disorders.
Blood Testing (Hemoglobin and Myoglobin)
Indicates status of kidney and urinary tract health; detects hematuria (presence of blood).
Differentiation between free hemoglobin and intact RBCs is essential.
Conditions leading to findings include kidney lesions, tumors, and infections.
Nitrite Testing
Utilized for rapid UTI detection and diagnosis alongside leukocytes.
Positive nitrite indicates bacterial conversion of nitrates; common UTI causing organisms include E. coli.
Leukocyte Esterase Testing
Detects urinary tract infections; indicates the presence of neutrophils (WBCs).
Utilizes diazo reaction; positive results are useful in conjunction with nitrite findings.
Glucose Testing
Helps diagnose and manage diabetes mellitus (presence of glucosuria).
High glucose levels lead to glucose spilling into urine once renal threshold is exceeded.
Ketone Testing
Measures ketone bodies: acetone, acetoacetic acid, β-hydroxybutyric acid.
Elevated levels indicative of fat metabolism for energy due to diabetes or starvation.
Bilirubin and Urobilinogen Testing
Serve as indicators of liver function; bilirubin indicates breakdown of RBCs.
Detection is critical for diagnosing liver diseases and any obstruction of bile flow.
Quality Control Procedures
Two levels of quality controls are run to ensure analyzers work properly: one normal level and one abnormal level.
QC vials must fall within specified ranges before proceeding with patient samples.
Actions taken if QC fails include checking vial date and mixing.
If both vials fail or issues persist, analyzer maintenance or recalibration may be necessary.