Urinalysis: Understanding Urine Tests and Results
Urinalysis: A Comprehensive Examination
A urinalysis, or complete urine examination, involves the physical and chemical analysis of urine, along with a microscopic examination of sediment obtained from centrifuged urine under standard conditions.
Urine Sample Integrity
The analysis can be compromised by delays or alterations that affect test quality:
- pH changes
- Lysis of leukocytes
- Loss of cylinders and cells
- Bacterial growth
- Decreased glucose
- Oxidation of bilirubin and urobilinogen
Preservation of Urine Samples
Proper preservation is crucial for accurate results. Here are some methods:
- Cooling: Store at 2-8°C at the bottom of the refrigerator.
- Toluene: 2 ml/100 ml – Suitable for quality control substances, but not for routine urinalysis.
- Formalin: 1 drop/30 ml – Good for preserving urinary sediment proteins.
- Thymol: A small amount – Interferes with protein precipitation.
- Conservative Tablets: 1 tablet/30 ml – Formaldehyde interferes with reducing substances and density, altering it by -0.005.
- Chloroform: Inhibits bacterial growth but modifies cellular sediment characteristics.
Normal Urine Volumes
- Normal urine volume: 1200-1500 ml/24 hours
- Polyuria: > 2500 ml/24 hours
- Oliguria: < 500 ml/24 hours
- Anuria: < 100 ml/24 hours
Urinalysis Components
A complete urinalysis includes:
- Physical Examination: Appearance, color, density
- Chemical Examination: pH, protein, glucose, ketone bodies, bilirubin, urobilinogen, hemoglobin
- Urinary Sediment Examination: Erythrocytes, leukocytes, pus cells, bacteria, cells, casts, crystals, other elements
Physical Examination: Appearance
Normal urine appearance is clear or transparent.
Causes of Turbidity
Turbidity may be due to:
- Precipitation of urate or amorphous phosphate crystals
- Large numbers of desquamated epithelial cells
- White blood cells or bacteria
Physical Examination: Color
Urine color can indicate various conditions:
- Chyluria: White
- Bilirubinuria: Coffee-Orange-Green
- Melanomas: Black
- Hematuria: Red
- Rifampicin: Red
- Crystalluria: Pink
- Myoglobinuria: Red
- Beets: Red
- Alkaptonuria: Black
- Porphyria: Red
- Nitrofurantoin: Brown
- Pyridium: Orange
Density Reference Values
Reference values for urine density:
- Random urine: 1.003 to 1.035
- 24-hour urine: 1.015 to 1.025
- Hyposthenuria: < 1.007
- Hypersthenuria: > 1.035
- Isosthenuria: = 1.010
Chemical Examination
Proteins
Normal protein excretion is 150 mg/24 hours. Elevated levels may indicate glomerular or tubular diseases, diabetes mellitus, SLE, vasculitis, etc.
Protein error of indicators: Tetrabromophenol Blue (3′,3″,5′,5″-tetrabromophenol sulfonphthalein). Color change: Yellow to green-blue.
Benign Proteinuria: Can be caused by fever, emotional stress, salicylate treatment, or intense exercise.
Glucose
Glucose should not normally be present in urine. Glycosuria is observed in conditions such as Diabetes Mellitus, Cushing’s syndrome, Acromegaly, Pancreatic Diseases, and Fanconi syndrome.
Renal threshold: ≈ 170 mg%
Glucose oxidase reaction: Light Green to Brown
pH
- Morning urine: 5 to 6
- 24-hour urine: 4.6 to 8
Indicator: Methyl red and bromothymol blue – yellow-green to blue
Acidic Urine
- Respiratory acidosis
- Metabolic acidosis
- Diabetic ketosis
- Infection with E. coli
Alkaline Urine
- Respiratory alkalosis
- Metabolic alkalosis
- Infection by Proteus and Pseudomonas
Ketones
Ketones appear in uncontrolled diabetes mellitus, vomiting and diarrhea, metabolic diseases, congenital metabolic disorders, febrile states, and fasting.
Ketone Bodies:
- Acetic acid
- Beta-hydroxybutyrate
- Acetone
Techniques to detect acetoacetic acid use sodium nitroprusside and alkaline buffer (pink-brown).
Increased ketosis is associated with reduced carbohydrate intake and Diabetes Mellitus.
Blood
Indicator: 3,3′,5,5′-tetramethylbenzidine – peroxide: HYDROPEROXIDE. Color change: Cumene blue-green to green.
False Positives: Hypochlorite, peroxidases, bacteria, menstrual blood.
False Negatives: High concentrations of ascorbic acid and red cells settling at the bottom of the container.
Hematuria
May indicate acute glomerulonephritis, lupus nephritis, renal tuberculosis, nephrotic syndrome, renal tumors, or Yellow Fever.
Hemoglobin
May appear in multiple pathologies, kidney stones, nephritis, and infections. Should be correlated with the urinary sediment.
Bilirubin
Not normally found in urine. Appears in biliary obstruction, pancreatitis, and hemolysis.
Contains salt 2 to 4 dichloro aniline diazonium. — Acre-purple
Reaction of iodine Smith:
False Positives: Chlorpromazine.
False Negatives: Ascorbic acid, nitrite, and biliverdin.
Increased Bilirubin: Hepatitis, Obstruction of the common bile duct.