What Tests Are Performed for Red & White Blood Cells in Urine?

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What Tests Are Performed for Red & White Blood Cells in Urine?
Normal urine speciman. (urine bottle image by alma_sacra from Fotolia.com)

Back pain and painful, frequent urination can send you racing to your doctor--or the nearest emergency room. The cause could be anything from a kidney stone to a urinary tract infection. Based on your symptoms, the doctor orders a urinalysis to see if there are many red cells--hematuria--or many white cells--leukocyturia--present in your urine. An occasional red or white cell in urine is normal--larger numbers are not normal and require treatment.

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Physical Exam for Red and White Cells in Urine

Physical examination is the first part of any urinalysis. The technician checks your sample for colour and appearance--clarity, turbidity, haziness or cloudiness. Normal urine is pale to dark yellow or amber in colour and clear. Red cells may tint the urine pink, red or brown, depending on the number of red cells present. If the red cells are broken or "lysed," the appearance may be clear; if the red cells are whole or "intact," the appearance may be hazy or turbid. White cells can cause the urine to appear cloudy without changing the colour.

The visual exam is the first step. Some foods and medications can cause the urine to appear abnormal, but the tech wouldn't discover that until the next step--the chemical exam of the urine.

Chemical Exam for Red and White Cells in Urine

Where the physical exam suggests the presence (or absence) of red and white cells in urine, the chemical test confirms or negates their presence. Chemical testing is carried out through the use of commercial reagent strips. The reagent strips are narrow plastic strips about 2 to 3 inches long with individual reagent impregnated test pads affixed along the length of the strip. The chemical reaction occurs when the strip is dipped in the urine sample. The pad that indicates the presence of blood on this strip will react with red cells and turn from yellow to green if red cells are present. The pad that indicates leukocyte esterase will react with white cells and turn from beige to violet if white cells are present.

Sometimes, there are not enough red or white cells to cause a colour change, and the only way to note their presence is by direct viewing as in the final--or microscopic--phase of a urinalysis.

What Tests Are Performed for Red & White Blood Cells in Urine?
Reagent strips for chemical testing of urine. (urine test image by Keith Frith from Fotolia.com)

Microscopic Exam for Red & White Cells in Urine

When all else fails, the microscopic examination, which is the final phase of a urinalysis, will allow the technician to see if red and white cells are present. After the chemical exam is done, the urine sample is spun down in a centrifuge. The supernatant--or top layer--is discarded, and a drop of the sediment--or bottom layer--is placed on a microscope slide on the microscope. The high-power objective is used to observe and count red and white cells per high-power field. Red cells show up as smooth biconcave disks, while white cells show up slightly larger, have a nucleus and, depending on which of the five possible white cell types are present, may be spherical or irregular-shaped.

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