Urinalysis Parameters

There are several parameters that can be determined during urinalysis, which can help to diagnose any abnormalities and guide treatment decisions. The most commonly used of these parameters are outlined in more detail below.

Urine Color

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. There are various factors that may influence the color of the urine, including dietary intake, medications and health conditions.

Clarity/Turbidity

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 be indicative of health conditions such as chyluria, pyuria, or phosphate crystals. However, it can also be influenced by other factors, such as vaginal discharge, sperm or prostatic secretions.

Acidity:

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 acidity of the urine 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 to monitor the response to medical treatment

Specific Gravity

The specific gravity represents the kidneys ability to concentrate the urine by comparing the amount of urinary solutes with respect to pure water. The normal values range between 1.005-1.025.

Low specific gravity may be indicative of impaired ability to concentrate urine, due health conditions such as diabetes insipidis, sickle cells nephropathy or acute tubular necrosis. Conversely, high values may be indicative of high protein or ketoacid concentration in the urine.

Glucose

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

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 be indicative of uncontrolled diabetes, diabetic ketoacidosis, intense exercise, starvation, vomiting and pregnancy.

Nitrates

Nitrates are not normally detected in the using but may be evident when there are bacteria present in the urine that can convert the nitrates. Bacteria that are 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 cause by one of these bacteria.

Other Parameters

There are various other factors that 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

References

• http://emedicine.medscape.com/article/2074001-overview#showall
• http://www.highlands.edu/academics/divisions/scipe/biology/labs/cartersville/2122/urinalysis.htm
• http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1413-86702007000500008&lng=en&nrm=iso&tlng=en
• http://www.roche-diagnostics.ch/content/dam/corporate/roche-dia_ch/documents/broschueren/professional_diagnostics/urindiagnostik/12254620001_EN_EA_Compendium-of-urinanalysis_Brosch%C3%BCre_EN.pdf