Several parameters can be determined during urinalysis, which can help diagnose any abnormalities and guide treatment decisions. The most commonly used of these parameters are outlined in more detail below.
The color of the urine appears due to the urochrome pigment and can change according to the concentration and chemical composition of the urine.
Urine color can vary from pale yellow when it is more diluted to a dark amber color when it is highly concentrated. Various factors may influence the color of the urine, including dietary intake, medications, and health conditions.
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The clarity of the urine if affected by substances in the urine, such as cellular debris, casts, crystals, bacteria or proteins. It is normally described as clear, cloudy, or turbid.
Cloudy or turbid urine may indicate health conditions such as chyluria, pyuria, or phosphate crystals. However, other factors can also be influenced, such as vaginal discharge, sperm or prostatic secretions.
The pH of the urine typically ranges from 4.5–8, which is slightly acidic due to the excretion of H+ ions via the renal system to maintain regular acid-base balance. Therefore, the urine's acidity will change according to the environment in the body and adjust to keep the rest of the body in balance.
Consumption of some foods (e.g., cranberries) can lead to more acidic urine, whereas other foods (e.g., citrus fruits) will reduce the acidity in the urine.
The urinary pH is a useful indicator for renal conditions such as infections, stones or renal tubular acidosis and can also help monitor the response to medical treatment.
The specific gravity represents the kidneys' ability to concentrate the urine by comparing the amount of urinary solutes concerning pure water. The normal values range between 1.005-1.025.
Low specific gravity may indicate impaired ability to concentrate urine due to health conditions such as diabetes insipidus, sickle cells nephropathy, or acute tubular necrosis. Conversely, high values may be indicative of high protein or ketoacid concentration in the urine.
The presence of glucose in the urine is known as glucosuria and is often indicative of diabetes mellitus, although it may be present in other circumstances (e.g., pregnancy). Normal levels are ≤130 mg/dL.
Ketones should not normally be present in the urine. However, they may accumulate when dietary intake of carbohydrates is low and the body relies on the metabolism of fats for energy. This process releases ketones such as acetone, acetoacetic acid and B-hydroxybutyric acid.
The presence of ketones in the urine may indicate uncontrolled diabetes, diabetic ketoacidosis, intense exercise, starvation, vomiting, and pregnancy.
Nitrates are not normally detected in the urine but may be evident when bacteria present in the urine can convert the nitrates. Bacteria capable of performing this conversion include E. coli, Klebsiella, Proteus, Enterobacter, Citrobacter, and Pseudomonas. For this reason, the presence of nitrates in the urine may indicate a urinary tract infection caused by one of these bacteria.
Various other factors may be determined in a urinalysis. The normal values for these are as follows:
- Leukocyte Esterase: Negative
- Bilirubin: Negative
- Urobilirubin: Small amount 0.5-1 mg/dL
- Blood: ≤3 red blood cells
- Protein: Protein: ≤150 mg/d
- Red Blood Cells: ≤2 RBCs/hpf
- White Blood Cells: ≤2-5 WBCs/hpf.
- Squamous epithelial cells: ≤15-20 squamous epithelial cells/hpf
- Casts: 0-5 hyaline casts/lpf
- Crystals: Occasionally
- Bacteria: None
- Yeast: None
Urinalysis - OSCE Guide