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Renal System: Diagnostic Tests Part 1

Updated: Jul 17, 2021

This video will cover the Renal System: Diagnostic Tests Part 1

Before we start, be sure to download the free PDF study guide to enhance your learning. Link is listed here.

Serum Creatinine Level

Creatinine is an end product of protein and muscle absorption. This test measures the amount of creatinine in the blood. If there is a high presence of creatinine in the blood, this indicates that there is a loss of the renal function, specifically the Glomerular filtration rate.

Blood Urea Nitrogen Level

This test measures the amount of nitrogenous urea which is made by the liver after protein is metabolized. Important to know for exams is that an elevated BUN level does not indicate renal disease. It can also indicate dehydration, a high protein diet, infection and many other causes. So if the BUN is elevated, it would be best to also analyze other diagnostic test results for confirmation.

BUN/creatinine Ratio

If the BUN and creatinine is both low or high, then this suggests renal disease. If the values are high, this could indicate fluid volume excess. If they are low, this occurs because of fluid volume deficit, obstructive uropathy and a high protein diet.


This test is used to evaluate the renal system. When obtaining a sample there are very important steps to take as a nurse that is constantly asked on exams and the NCLEX.

How to Obtain a Basic Urinalysis

  1. Wash perineal area and use a clean container for collecting urine

  2. Obtain 10 to 15 mL of the first morning void if possible.

  3. Do not refrigerate the sample as this can alter results.

How to Obtain a 24 Hour Urine Collection

  1. Check the doctor's order about specific instructions for the client to follow such as dietary and medication restrictions.

  2. Provide instructions about the urine collection

  3. When the collection starts, remember the exact time and explain to the patient to discard their first void.

  4. Only after the first void is discarded can the patient start collecting the urine for the next 24 hours.

  5. Keep the urine specimen on ice or refrigerated.

  6. At the end of the 25 hour mark, the patient will add their final void into the collection container.

Specific Gravity

This test measures how well the kidneys work to concentrate urine. Factors that interfere with an accurate reading are cold specimens so never refrigerate specimens. The normal range reference is 1.005 to 1.030. An increase in specific gravity such as 1.040 indicates insufficient fluid intake or decreased renal perfusion. A decrease in specific gravity such as 1.001 indicates increased fluid intake or diabetes insipidus. This could also indicate renal disease or kidney issues.

Urine Culture and Sensitivity Testing

This test is used to identify the presence of bacteria and determines which specific antibiotics will treat the bacteria. Bacteria is known as culture and the antibiotic to kill the bacteria is known as sensitivity. Collecting a culture and sensitivity test correctly is vital and always asked on exams.

How to Collect a Urine Culture and Sensitivity Test

  1. Clean the perineal area and urinary meatus with a bacteriostatic solution. This will help to make sure the results of the type of bacteria are accurate.

  2. Have the patient collect a midstream sample which means the patient will void first then collect while voiding. This method is called a Clean Catch specimen.

  3. As soon as the sample is collected, it needs to be sent to the lab immediately.

  4. Most important thing to note is that the specimen needs to be free from containmates which include hair, skin or secretions. If there were any type of contamination, the sample must be discarded.

Creatinine Clearance Test

This test is used to measure how well the kidneys are able to remove creatinine from the blood. This test also measures the GFR which is known as the Glomerular filtration rate. The Creatinine Clearance Test is the best method to determine the GFR. A normal GFR is 125 mL/minute. With this test, the nurse would be collecting blood and urine samples. The urine sample is done like the 24 hour urine collection, then after 24 hours, blood labs are drawn.

Bladder Ultrasonography

This test is a way to scan the bladder. It is a non-invasive safe method that determines the volume of urine in the bladder. It can also be used to check for urinary frequency, inability to urinate and the amount of urine that stays in the bladder after voiding.

Intravenous Urography: Before the Test

This x-ray procedure involves IV injection of a radiopaque dye that helps visualize the vessels of the renal system. The most important concept to remember for exams is that the nurse must assess for allergies to iodine, seafood and dyes. This radiopaque will harm a patient with a history of allergies. If the patient does have a history, this procedure is a contraindication which means it cannot be performed.

Other contraindications include a positive pregnancy test, asthma and cardiac disease.

If the patient can undergo the procedure, food and fluids will be withheld. The doctor may prescribe laxatives. Before the procedure begins, it's important for the patient to know what to expect. Throat irritation, flushing of the face, warmth or a metallic taste is expected during the test.

Intravenous Urography: After the Test

After the test, there are important assessments that must be done.

  1. Monitor vital signs, making sure they are within the normal range, otherwise interventions must be made.

  2. Instruct the patient to drink at least 1 Liter of fluids to flush the dye out of their system. Fluids will also make the dye dilute and easier on the kidneys. This is vital to know.

  3. Monitor the urinary output. If the patient isn’t voiding, the dye will damage their kidneys.

  4. Monitor for signs of an allergic reaction.

  5. Educate the patient on signs of an reaction and to call their provider if it occurs.

  6. Please remember that the dye is very damaging to the kidney so there is a greater risk for older patients.

Well that concludes this video, join us in the next video as we cover part two of diagnostic tests. Thanks for watching!

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