Urinalysis: Composition and Examination

Urine Composition

• Urine is a complex aqueous mixture consisting of 95% water and 5% dissolved substances.
• Nitrogenous wastes in urine: urea, uric acid, and creatinine.
• Other normal solutes in urine: Na+, Cl-, K+, PO34-, SO42-, Ca2+, Mg2+, HCO3-.
• Abnormally high concentrations of any urinary constituents may indicate pathology.

Urine Composition: Urea

• Urea is a water-soluble compound, CO(NH2)2, that is the major nitrogenous end product of protein metabolism.
• Breakdown of proteins by the body, during which amino groups are removed from amino acids and converted into ammonia, which is then converted into urea by the liver.
• High urea excretion results from high protein diet or conditions associated with an increased protein catabolism (e.g., diabetes mellitus).

Urine Composition: Uric Acid

• Uric acid is the end product of purine metabolism.
• 75% of uric acid is excreted in urine by the kidneys, while the remaining 25% is secreted into the gastrointestinal tract.
• Uric acid exists mainly as urate in synovial fluid and plasma, and can combine with sodium to form monosodium urate crystals.

Urine Composition: Creatinine

• Creatinine is a breakdown product of creatine and will be excreted by the kidneys in the urine at a constant rate, depending on muscle mass.
• Creatine is a naturally occurring amino acid found in the muscle.

Collection and Preservation of Urine Sample

• Type of urine specimens: first morning, random, postprandial, midstream clean catch, 24-hour, catheter, suprapubic aspiration, and pediatric.
• Each type of urine specimen has its own specific purpose and collection method.

FEME Analysis

• Urinalysis consists of physical observation, chemical analysis, and microscopic examination.
• FEME Chemistry test uses dipstick method.
• FEME Microscopic observation examines particles such as cells, bacteria, casts, and crystals.

Physical Observation

• Physical properties of urine include: volume, color, transparency, odor, and specific gravity.
• Normal urine volume: 1.2–1.5L.
• Abnormalities in urine volume: oliguria, polyuria, anuria, and nocturia.
• Normal urine color: pale yellow to deep amber.
• Abnormalities in urine color: due to pathologic conditions, certain foods, and drugs.
• Normal urine transparency: clear or transparent.
• Abnormalities in urine transparency: due to epithelial cells, mucus, sperm, prostatic fluid, RBCs, WBCs, or bacteria.
• Normal urine odor: faint aromatic odor.
• Abnormalities in urine odor: due to certain metabolites, such as acetone, ammonia, and phenylketonuria.
• Normal urine specific gravity: 1.005 – 1.030.
• Abnormalities in urine specific gravity: due to dehydration, diabetes mellitus, proteinuria, overhydration, chronic renal diseases, and renal tubular damage.

FEME Chemical Observation

• Chemical properties of urine include: pH, protein, glucose, ketone, blood, bilirubin, urobilinogen, nitrite, and leukocyte esterase.
• Normal urine pH range: 4.6 – 8.0 (average 6.0).
• Abnormalities in urine pH: due to diabetes, starvation, systemic acidosis, or a diet high in meat products and cranberries, and bacteria, urinary tract infection, or a diet high in citrus fruits and vegetables.

Learn about the composition of urine, urine sample collection and preservation, types of urine specimens, and FEME analysis including physical, chemical, and microscopic examination of urine.