Urinalysis

UrinalysisWhat is Urine?

Urine is a product of kidney secretion through which the body eliminates waste products of metabolism, unnecessary and excess substances. In healthy individuals, urine liquid color ranges from clear to pale yellow, with a distinct odor.

Urinalysis

Urinalysis is a routine and one of the most common laboratory tests. The results provide valuable information about the overall condition of the body. It is used as a screening test during routine check-ups or for monitoring specific health conditions such as urinary tract infections, kidney diseases, liver disorders, and diabetes. When we refer to urinalysis, it typically means a general urine examination with sediment, which includes standard laboratory tests.

What is a General Urine Examination?

A general urine examination includes:

Physical examination of the urine
Semiquantitative chemical examination of the urine
Microscopic examination of the sediment

Physical Examination of Urine

Physical Examination of UrineUrine Appearance

Normal finding: Clear urine. If urine is cloudy, this may be due to the presence of salts, mucus, or other elements, or it could indicate an inflammatory process.

Physical Examination of UrineUrine Color

Normal finding: Yellow, ranging from light yellow to dark yellow. The color depends on the amount of fluid intake—more concentrated urine is darker. Urine color changes during acute conditions (fever, diarrhea, vomiting). In cases of elevated bilirubin in the blood, the urine may appear dark brown. If bleeding occurs in the urogenital tract, urine may be red, indicating hematuria (presence of blood in the urine).

Physical Examination of UrineUrine pH

Normal range: 4.6 to 8.0 pH units (acidic to slightly alkaline). The average pH value in healthy individuals is 6.0. The pH of urine depends on diet. For example, people who consume a lot of meat and protein tend to have acidic urine because the breakdown of proteins produces phosphoric and sulfuric acids, which are excreted as acidic salts (phosphates and sulfates). Individuals on a plant-based diet (e.g., vegetarians) tend to have alkaline urine, as carbonic acid is excreted as carbonates. Extremely alkaline urine can result from improper storage of the urine sample. Prolonged exposure to room temperature leads to a chemical reaction that converts urea into ammonia due to bacterial activity, increasing the pH of urine. Proper storage and transport of urine samples are crucial. Alkaline urine may also indicate a urinary infection.

Physical Examination of UrineSpecific Gravity of Urine (Relative Density)

Normal finding: Yellow, from light yellow to dark yellow. The color varies based on fluid intake—more concentrated urine is darker. The urine color can change during acute conditions (fever, diarrhea, vomiting). When blood bilirubin is elevated, the urine may become dark brown. Red urine, indicating hematuria (blood in urine), may occur when bleeding in the urogenital tract is present.

Semiquantitative Chemical Urinalysis

This test involves detecting the presence of certain substances that should not be present in the urine of healthy individuals or substances that cannot be detected by other means. For this purpose, test strips are used, primarily multiple reagent strips (for detecting several substances on one strip), which are based on dry chemistry and have good sensitivity and specificity. The following substances are detected in this way:

Proteins

Normal finding: Negative.
Positive protein results can occur during pregnancy or after intense physical activity, and may also be a sign of an inflammatory process if other indicators of inflammation are present.

Glucose

Normal finding: Negative.
A positive glucose result is observed when blood glucose levels exceed 10 mmol/L, which typically indicates Diabetes mellitus (diabetes).

Ketone Bodies (Acetone, Acetoacetate)

Normal finding: Negative.
Ketones are produced by the breakdown of fats and fatty acids when the body is deficient in carbohydrates, as this provides the necessary energy.
A positive result is commonly seen in individuals following high-protein, restrictive diets, after strenuous physical activity, prolonged fever, and most frequently in diabetics, indicating inadequate therapy.

Ascorbic Acid (Vitamin C)

Finding: Can be either positive or negative.
Excess vitamin C is excreted from the body through urine. A positive result is not pathological.
It is important for interpreting results because the presence of vitamin C in the urine can interfere with certain chemical reactions, such as the detection of glucose and hemoglobin in urine.

Bilirubin

Normal finding: Negative.
Bilirubin is a yellowish pigment produced by the breakdown of hemoglobin in the liver, passes into bile and into the small intestine.
A positive bilirubin result in urine is typically found in patients with liver disease or bile duct disorders.

Urobilinogen

Normal finding: Present in urine up to 0.2 mg/dL.
Urobilinogen is produced from bilirubin in the intestines.
Elevated urobilinogen levels occur due to liver diseases or conditions associated with increased breakdown of red blood cells (hemolysis).

Nitrites

Normal finding: Negative.
Positive nitrites in urine indicate an acute urinary infection. However, it is possible for nitrites to be negative even when a patient has a urinary infection. This occurs when bacteria that do not have the ability to convert nitrates to nitrites are present.

Hemoglobin

- Normal finding: Negative.
- The presence of hemoglobin in urine is a result of blood in the urine, known as hematuria.

Microhematuria refers to bleeding that is not visible to the naked eye and is only detected through microscopic examination.
Macrohematuria refers to more significant bleeding, which changes the urine color from yellow to red.

Microscopic Examination of Sediment

The microscopic examination of urine sediment includes both organized (biological) and unorganized (chemical) sediment.

Organized Sediment: Comprises blood cells (leukocytes and erythrocytes), epithelial cells, casts, and other forms such as fungi, spermatozoa, and bacteria.
Unorganized Sediment: Consists of crystals or amorphous deposits of various compounds.

Therefore, it is clear that the organized part of the sediment is far more significant than the chemical.

Erythrocytes

Normal finding: Should not be present in urine or may be present in very small numbers (1-2 erythrocytes per high-power field).
An increased number of erythrocytes in urine indicates hematuria (bleeding), which can originate from any part of the urinary tract.
Erythrocytes can be fresh or shriveled. Fresh erythrocytes may be due to the presence of urinary stones or sand. Shriveled erythrocytes typically indicate a past infection or chronic kidney disease.
Erythrocytes can also be found in patients who engage in intense physical activities or have experienced injuries.

Leukocytes

Normal finding: Up to 5 leukocytes per field of view (400x magnification).
An increased number of leukocytes or a positive test for leukocyte esterase indicates the presence of an inflammatory process.
In urinary infections, an elevated leukocyte count is typically accompanied by the presence of bacteria in the sediment, suggesting the need for a bacteriological examination of the urine, or a urine culture.

Epithelial Cells

Types: Squamous and round.
They originate from the mucosa of the urinary tract, covering the entire urinary and genital tract, and generally do not have clinical significance.
Normally present in small numbers in the sediment due to the constant shedding of the mucosa.

Casts

Formation: Casts are formed in the lumen of the renal tubules through the homogenization of proteins. These coagulated proteins are primarily observed in cases of proteinuria (elevated protein levels in urine). In some cases Hyaline Casts can be found in healthy individuals, often due to intense physical activity or dehydration. Cellular, Granular, and Waxy Casts usually indicate pathological conditions.

Bacteria

Urine is not a sterile liquid, so a small number of bacteria can be present. Results are reported as rare, few, moderate, or many bacteria. Moderate and many bacteria suggest a urinary infection.
It is crucial to collect the urine sample correctly to avoid contamination, which can lead to falsely elevated bacterial counts due to saprophytic flora from the mucosa being washed into the sample.

Fungi

Normal finding: Should not be present in urine sediment.
Presence of fungi indicates a fungal infection.

Spermatozoa

Normal finding: Should not be present.
Their presence, especially in older men, can indicate prostate damage.

The chemical component of sediment is less significant compared to the organized (biological) part but still provides information about the overall condition of the body.

Crystals and Salts

Some crystals that are normally found in urine sediment, and they are divided into acidic and alkaline normal crystals. Acidic crystals include amorphous urates, uric acid crystals, acid urates, calcium oxalate, etc. Normal alkaline crystals include amorphous phosphates, triple phosphate, calcium carbonate, calcium phosphate, etc. Crystals of cholesterol, tyrosine, bilirubin, leucine, cystine, and others may appear n pathological conditions.

Mucus

It has no significant clinical relevance.

To ensure the urine test results are valid and useful, every step of the pre-analytical phase as well as the analytical phase (i.e. laboratory work performed by skilled personnel) must be followed. The laboratory staff is responsible for informing the patient about the proper way to collect a urine sample for analysis. For a urine test, the first morning urine (midstream) should be taken after genital hygiene, and collected in a sterile container. It is crucial that the sample is delivered to the laboratory no later than two hours after urination, and until the sample should be kept cool (refrigerated). Urine sampling should not be performed during the menstrual cycle.