The major function of the urinary system is to remove waste products from our bodies and help regulate the volume and composition of blood by the production and excretion of urine. The urinary system consists of two kidneys, two ureters, one bladder, and one urethra..
The composition of urine can vary greatly and constantly fluctuates with dietary intake (food and water) and metabolic activity. Urine consists mostly of water with various organic and inorganic substances such as urea, uric acid, creatine, sodium chloride, ammonia, sulfates, and phosphates as its principal ingredients. A clinical examination of urine can provide a convenient, cost effective and non-invasive means of assessing kidney function and providing an overall assessment of our body's health.
Typically, a complete urinalysis involves an examination of the physical characteristics of urine, a chemical analysis and a microscopic examination of urine sediment. Urine should be collected in a clean container, stored in a cool place, and tested as soon as possible.
NOTE: Please use caution in the handling of urine specimens. Only handle your own urine! Discard cups, urine, and dipsticks as indicated by the instructor. Disinfect all equipment and tabletops with 10 percent bleach following the exercise. Latex gloves may be used. READ ALL OF THE FOLLOWING REFERENCE MATERIALS AND INSTRUCTIONS BEFORE PERFORMING ANY PART OF THE URINALYSIS. THEN RECORD YOUR DATA IN THE FOLLOWING CHART:
|color and odor|
|bacteria or yeast|
A. PHYSICAL CHARACTERISTICS OF URINE
The physical characteristics of urine include observations and measurements of color, turbidity, odor, specific gravity, pH and volume. Visual observation of a urine sample can give important clues as to evidence of pathology.
The color of normal urine is usually light yellow to amber. Generally the greater the solute volume the deeper the color. The yellow color of urine is due to the presence of a yellow pigment, urochrome. Deviations from normal color can be caused by certain drugs and various vegetables such as carrots, beets, and rhubarb.
Slightly aromatic, characteristic of freshly voided urine. Urine becomes more ammonia-like upon standing due to bacterial activity.
Normal urine is transparent or clear; becomes cloudy upon standing. Cloudy urine may be evidence of phosphates, urates, mucus, bacteria, epithelial cells, or leukocytes.
Ranges from 4.5 - 8.0. Average is 6.0, slightly acidic. High protein diets increase acidity. Vegetarian diets increase alkalinity. Bacterial infections also increase alkalinity.
5. SPECIFIC GRAVITY
The specific gravity of urine is a measurement of the density of urine - the relative proportions of dissolved solids in relationship to the total volume of the specimen. It reflects how concentrated or dilute a sample may be. Water has a specific gravity of 1.000. Urine will always have a value greater than 1.000 depending upon the amount of dissolved substances (salts, minerals, etc.) that may be present. Very dilute urine has a low specific gravity value and very concentrated urine has a high value. Specific gravity measures the ability of the kidneys to concentrate or dilute urine depending on fluctuating conditions. Normal range 1.005 - 1.035, average range 1.010 - 1.025.
Low specific gravity is associated with conditions like diabetes insipidus, excessive water intake, diuretic use or chronic renal failure.
High specific gravity levels are associated with diabetes mellitus, adrenal abnormalities or excessive water loss due to vomiting, diarrhea or kidney inflammation. A specific gravity that never varies is indicative of severe renal failure.
Specific gravity can be
determined by either of two methods using a refractometer or a
a. Refractometer - measures the refractive index of urine which parallels the specific gravity.
1. Collect mid-stream sample of urine in collection cup.
2. Pipette 1-2 drops of urine into the plastic chamber located on the top of the refractometer. Be sure that the plastic is pressed firmly down in place on the refractometer.
3. Determine the specific gravity of the urine by looking through the refractometer and determining the value on the scale on the left hand side. The specific gravity value is where the light and dark intersect on the scale.
4. Clean the refractometer with kimwipes.
b. Urinometer - Is a weighted, bulb shaped device that has a specific gravity scale on the stem end.
1. Fill the cylinder with enough urine so that the urinometer will float in the urine and not touch the bottom.
2. Be careful not to drop the urinometer in the cylinder! Gently release it in order not to break or burst the cylinder. It should NOT touch the sides or bottom of cylinder.
3. The specific gravity can be read on the scale on the stern of the urinometer at the meniscus.
4. The specific gravity of water is 1.000 with respect to temperature. The urinometer can be checked periodically against this standard to ensure quality control at that temperature.
(* For very precise and exacting measurements of specific gravity, corrections should be made +/- .001 for each 3° C above or below 25° C. Add .001 if above 25° C, subtract .001 if below 25°C.
B. CHEMICAL ANALYSIS
For routine chemical analysis of urine there are several brands of chemical test strips (dip sticks) that are commercially available. These urinalysis test strips have small test patches impregnated with various chemicals in order to detect the presence or absence of certain substances. Qualitative and/or quantitative results can be obtained depending on the particular test.
Take a specimen cup from the lab to the bathroom; void into the cup and return to the lab.
- Briefly (one second or less) dip the test strip into the urine. Make sure that all test
squares are immersed.
- Draw the edge of the strip along the rim of the specimen cup to remove excess urine.
- After the appropriate times (as indicated on the vial of strips) read the tests by
comparing to the color chart on the edge of the vial.
PLEASE DO NOT TOUCH THE TEST STRIP TO THE COLOR CHART. IF YOU DO SO
ACCIDENTALLY, IMMEDIATELY WIPE THE VIAL WITH DISINFECTANT.
- NOTE: For convenience, all values on the strip may be read between 1 and 2 minutes after immersion. The colors are stable for up to 120 seconds after immersion. Color changes that occur after 2 minutes from immersion are not of diagnostic value. Color changes that occur only along the edge of the test area should be ignored.
- Results are obtained by direct visual comparison with the color scale printed on the vial
label. No calculations are necessary. Record your results.
- NOTE: For such a test to be considered clinically acceptable for a valid diagnosis, careful quality control should be maintained, i. e. expiration dates respected, environmental conditions stabilized, etc. In a teaching lab these conditions are not met. You can learn the procedure and see some variable results among the class members, but do not base any clinical assumptions on the results obtained in this lab. If you have any
reason to suspect a clinical problem, go to a licensed medical laboratory for a urinalysis.
|ABNORMAL CONSTITUENT:||ASSOCIATED CAUSES:|
|Protein (albumin) –||Albumin is normally too large to pass through glomerulus. Indicates abnormal increased permeability of the glomerulus membrane. Non-pathological causes are: pregnancy, physical exertion, increased protein consumption. Pathological causes are: glomerulonephritis bacterial toxins, chemical poisons.|
|Glucose –||Glycosuria is the condition of glucose in urine. Normally the filtered glucose is reabsorbed by the renal tubules and returned to the blood by carrier molecules. If blood glucose levels exceed renal threshold levels, the untransported glucose will spill over into the urine. Main cause: diabetes mellitus|
|Ketones –||Ketone bodies such as acetoacetic acid, beta-hydroxybutyric acid, and acetone can appear in urine in small amounts. These intermediate by-products are associated with the breakdown of fat. Causes: diabetes mellitus, starvation, diarrhea|
|Bilirubin –||Bilirubin comes from the breakdown of hemoglobin in red blood cells. The globin portion of hemoglobin is split off and the heme groups of hemoglobin is converted into the pigment bilirubin. Bilirubin is secreted in blood and carried to the liver where it is conjugated with glucuronic acid. Some is secreted in blood and some is excreted in the bile as bile pigments into the small intestines. Causes: liver disorders, cirrhosis, hepatitis, obstruction of bile duct|
|Urobilinogen –||Bile pigment derived from breakdown of hemoglobin. The majority of this substance is excreted in the stool, but small amounts are reabsorbed into the blood from the intestines and then excreted into the urine. Causes: hemolytic anemias, liver diseases|
|Hemoglobin –||Hemoglobinuria is the presence of hemoglobin in the urine. Causes: hemolytic anemia, blood transfusion reactions, massive bums, renal disease|
|Red blood cells –||Hematuria is the presence of intact erythrocytes. Almost always pathological. Causes: kidney stones, tumors, glomerulonephritis, physical trauma|
|White blood cells –||The presence of leukocytes in urine is referred to as pyuria (pus in the urine). Causes: urinary tract infection|
|Nitrite –||Presence of bacteria. Causes: urinary tract infection|
C. MICROSCOPIC EXAMINATION
Examination of urine sediment may reveal the presence of different types of cells such as epithelial cells, leukocytes, erythrocytes, or renal cells. Different types of crystals, yeast, bacteria, or casts may also be present. Casts are cylindrical structures created by protein precipitation in the renal tubules.
1. Transfer urine sample to a conical centrifuge tube.
2. Centrifuge your sample at a moderate speed for 5 minutes. BE SURE TO
3. Discard the supernatant (fluid off the top) by quickly pouring off fluid.
4. Tap tube with index finger to mix sediment with remaining fluid.
5. Make a wet mount of sample by transferring 1 drop of material to a slide and
covering with a coverslip.
6. Examine the sample under the microscope under low and high power.
7. Identify what you see by comparing to charts. Draw a few of your observations.
FOR THE PRACTICAL, BE ABLE TO RECOGNIZE ANY OF THE EQUIPMENT USED, NAME IT, AND DESCRIBE ITS FUNCTION. BE ABLE TO NAME A POSSIBLE CAUSE OF A HIGH READING FOR ANY OF THE MATERIALS EVALUATED. BE ABLE TO NAME A COMMON ITEM FOUND IN THE URINE BY MICROSCOPIC EXAMINATION. BE ABLE TO RELATE A SPECIFIC GRAVITY VALUE TO THE CONCENTRATED/DILUTE STATUS OF URINE.