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Urinalysis

Urinalysis referred as urine analysis or urine test is a procedure wherein the urine from an individual is studied to identify the presence or to rule out certain underlying disorders or conditions.

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These disorders may be specific to the urinary system or being a general disorder such as diabetes.

Types of Urinalysis

Urine is one of the end products of the body’s metabolic processes. Normally, urine has a specific appearance and contains traces of various by products. Any variations in these characteristics may suggest an abnormality though certain variations are noted normally.

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There are different methods to analyze a urine sample and the method followed is based on the provisional diagnosis and the disorder suspected.

These methods can be categorized as:

  • Macroscopic urinalysis
  • Chemical urinalysis
  • Microscopic urinalysis
  • Urine culture1,2

Macroscopic Urinalysis

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This is usually the first step in urinalysis wherein the urine sample is visualized directly with naked eye to check for the color, presence of any particles and for turbidity or cloudiness of the urine.  

Normal urine is pale to dark yellow or amber colored, devoid of any particles and clear. Abnormal conditions such as macroscopic hematuria are  characterized by reddish urine owing to the presence of red blood cells in the urine. However, certain foods, dyes and medications may also result in change in the color of the urine.

Chemical Urinalysis

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This process involves introducing certain chemicals or reagents to the urine sample to identify a specific condition. These chemicals may either be added manually or through certain specialized instruments known as dipsticks. The pregnancy kit is one of the examples of chemical urinalysis wherein the presence of a hormone in pregnant women activates the chemical present in the kit resulting in a change of color to confirm pregnancy.

The chemical analysis is usually advised to:

  • Know the pH of urine (whether it is acidic or alkaline).
  • Measure the specific gravity of urine (helps in identifying the functioning ability of the kidneys).
  • Detect the presence of certain substances such as proteins, glucose, ketones, bilirubin, nitrites, etc. (these may either be absent under normal circumstances or may be at certain normal levels in urine)  

The chemical analysis may serve the purpose of specifically identifying the underlying disorder or may prove vital clues for other investigations.

Microscopic Urinalysis

This type of analysis is considered as an indispensable tool for the detection of certain disorders those otherwise remains asymptomatic. A single drop or a few drops of the urine is studied under the microscope to detect the presence of cells, casts, crystals and bacteria. Presence of cells such as blood cells and other varieties of cells that may point to the underlying disorder is verified. Casts are certain types of proteins when present indicate the specific area of the urinary system that may have been affected.

Normally, the urine consists of crystals such as calcium oxalate crystals. In certain abnormal cases such as formation of kidney stones, increased number and certain specific types of crystals diagnostic of the condition are noted. Identification of the presence and the type of bacteria present in the urine can also be done during microscopic urinalysis.

Urine Culture   

Urine culture may be advised if an infection of the urinary system is suspected. In certain instances, it is also advised to identify the specific group of organism in order to plan the treatment appropriately.1 - 4

Urine Collection Methods

The urine sample may be collected in different methods, which include:

Random sample

Urine collected at any time of the day without any specific instructions.

Early morning sample

Urine is collected as soon as an individual wakes up in the morning and before taking any fluids.

Clean catch, midstream sample

This method is followed to prevent false interpretations due to the presence of certain pathogens in the area around the genitals. The urine is collected after first half of the urine is discarded.

Surgical collection

Urine may be collected by introducing a catheter or a needle in certain special circumstances.2,5

Conditions for Which Urinalysis is Advised

Urinalysis may be advised for a wide variety of conditions/disorders either as a specific diagnostic test or as a routine test to rule out the presence of any underlying pathologies.

Some of the conditions or disorders for which urinalysis is commonly advised include:

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References:

1. Simerville JA, Maxted WC, Pahira JJ. Urinalysis: A Comprehensive Review. Am Fam Physician. 2005; 71: 1153–1162.

2. Available at: http://library.med.utah.edu/WebPath/TUTORIAL/URINE/URINE.html. Accessed on: 02-07-2008

3. Ochoa Sangrador C, Conde Redondo F; Grupo Investigador del Proyecto. Utility of distinct urinalysis parameters in the diagnosis of urinary tract infections. An Pediatr (Barc). 2007; 67(5): 450–460.

4. Whitfield HN. Urological evaluation. BMJ 2006;333:432–5.

5. Ochoa Sangrador C, Brezmes Valdivieso MF; Grupo Investigador del Proyecto. Sample collection methods for urine culture and analysis. An Pediatr (Barc). 2007;67(5): 442–449.

6. Smellie WS, Forth JO, McNulty CA, Hirschowitz L, Lilic D, Gosling R, et al. Best practice in primary care pathology: Review 2. J Clin Pathol. 2006; 59: 113–120.