Recap: In the previous blog , we studied about the abnormalities/changes that are usually observed in urine and its properties and associated medical conditions.
Urine analysis (UA) is a set of tests performed on or using urine as a test sample. These tests help detect medical conditions related to kidneys, urinary tract and overall metabolic well-being of an individual. These tests are performed to detect illness or aids in diagnosis of kidney diseases, liver diseases, urinary tract infections (UTI), diabetes, etc. UA is a part of pregnancy checkups, too.
Urine analysis includes checking the appearance, concentration and contents of urine. Deviations from normal urine may indicate the presence of a medical condition or a health hazard.
UA comprises of the physical, chemical and microscopic examination of urine.
Process of Urine Collection
1. Drinking plenty of water prior to urine is recommended (not excess).
2. Administration of any medication is to be told to the physician, as drugs can alter the UA results.
3. The midstream urine is collected in a urine cup and is secured with a lid.
4. In some cases, catheter is used for urine collection.
Tests performed in Urine-analysis
A) Visual Examination- The color and turbidity of urine is examined in this test. Appearance of turbidity may indicate bacterial or fungal contamination. Cloudiness in urine is indicative of the presence of proteins in urine. Colored urine indicates kidney abnormalities, dehydration, and hematuria. E.g. Red urine is indicative of presence of RBCs in urine i.e. hematuria.
B) Microscopic examination- A small amount of urine is observed under a microscope. Sample is checked for red blood cells, white blood cells (or pus cells), bacteria (germs), or crystals (which later on become kidney stones after enlargement).
C) Rapid urine tests- These tests are also called as dip-stick tests. They test for the chemical composition of urine. A test strip is dipped into the urine and is compared with the colored fields on the packaging. Depending on the concentration of the particular substance being tested, the fields on the test strip change color. The color table on the urine test package indicates normal and abnormal values. Figure 1 shows a representation of tests performed by dipstick method for UA.
Figure 1. Test performed by Dipstick method
Figure 2 provides the normal and pathological values of various tests used in UA and their probable inferences.
Figure2. Normal and pathological values of various tests used in UA and their probable inferences.
24-hour urine test
Normally 100-250mL urine is collected in a urine cup. In 24 hour urine, patient needs to collect urine throughout the day (24-hour period of time) in a special container. Amounts of various substances in the urine changes during the course of a day. As a result, examining a 24-hour urine sample instead of a random urine sample becomes important. By collecting the urine completely for 24 hours, the amount of the substance being measured (like, protein, creatinine, urea, nitrogen, etc.) in the urine can be averaged over the entire day and will better indicate of what is happening in the body. This test tells the quantity of protein, hormones, salts and creatinine are present in the urine/excreted through the urine after it is collected for an entire day.
Urinary Creatinine
Creatinine is a waste product formed by muscle metabolism. A normally functional kidney filters creatinine from blood and is excreted through urine. Creatinine test is a crucial parameter indicating the state of kidney function. Figure 3 puts forth normal values of urine creatinine levels.
Figure 3. Normal urinary creatinine per 24 hours levels in males and females
Creatinine values above the normal range may be an indication of kidney disease, kidney infection, kidney failure, kidney stones, late-stage muscular dystrophy, myasthenia gravis or diabetes.
Urinary Protein
The extent of proteinuria is determined by testing the levels of proteins excreted through urine. For random/spot urine sample, the level of proteins should be less 11.9 mg/dl whereas for a 24-hour sample, the value should be less than 149.1 mg/24 hours.
Urinary Urea and Nitrogen
Proteins consumed through foodstuffs are broken down to nitrogen-based products and excreted through urine as urea. The test measures the levels of urea and nitrogen as the indicator of kidney function in the urine sample collected over the 24-hour period. 12-20 g/24-hour is considered as a normal range of urea and nitrogen in the urine sample.
Urinary Protein/Creatinine ratio
Urine protein/creatinine ratio is calculated as: (Urine protein (g/L) X 1000)/ Urine Creatinine (mmol/L)
Urine protein/creatinine ratio is an important indicator of kidney disease and follow-up testing is required for monitoring the progress of the disease. The ratio should be lower than 0.2 for a random urine sample/spot urine sample.
Urine culture
The urine sample is added into petri-plates with a growth medium and is incubated for 24-48 hours to observe for the growth of microorganisms. If there are bacteria or fungi in the urine, visible colonies of these microorganisms grow. This test is done to detect or confirm UTIs. The effective antibiotic for the infection can be determined on the basis of the results of this test. Figure 4 shows the representation of urine culture tests showing the growth of microbes on petri-plates.
Meaning of scientific terms
1. Catheter - A soft hollow tube passed into the bladder to drain urine.
2. Diabetic ketoacidosis - A serious complication of diabetes which occurs when body produces high levels of blood acids called ketones. The condition develops when body can't produce enough insulin.
3. Hepatitis - A viral infection that causes swelling of the liver tissue.
4. Midstream urine - Urine collected midway through the urination process.
5. Muscular dystrophy – A group of inherited diseases that damage and weaken muscles over time.
6. Myasthenia gravis - Neuromuscular disease which leads to skeletal muscle weakness.
7. mg - Milligram
8. ·mmol- Millimoles, denotes concentration
9. Petri-plates - Small glass dish covered with lids.
10. Colonies - An accumulation of microbes/cluster of microbes grown on the culture plate
References
6. https://www.ncbi.nlm.nih.gov/books/NBK279350/Understanding urine tests
About the author:
Janhavi is a graduate in Microbiology from Fergusson College, Pune and holds a post-graduate degree in Biological Sciences from NMIMS University, Mumbai. She had been a project trainee at ACTREC, Navi Mumbai and was formerly associated as Assistant Professor in Biotechnology at CKT college of ACS, Navi Mumbai. The science of cancer biology, therapeutics, nanomedicine and immunology fascinates her the most. Besides this, she loves to cook, exercise and travel.