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Health Library : Lab Tests & Results Print [PDF]
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Creatinine measurement, 24 hour urine

What is this test?

This test measures creatinine (a product of protein breakdown) in urine and blood. It is used to determine glomerular filtration rate, which helps to measure how well the kidney functions[1][2]. This test may be used in suspected cases of gout[3], impaired kidney function[4][5]and kidney disease in diabetic patients[4][6][7].

Why do I need this test?

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. The following are possible reasons why this test may be done:

  • Diabetic kidney disease
  • Impaired kidney function

When and how often should I have this test?

When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.

Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.

The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.

How should I get ready for the test?

Venous blood:

Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.

24 hour urine collection:

During a 24-hour urine collection, follow your usual diet and drink fluids as you ordinarily would, unless healthcare workers give you other instructions. Avoid drinking alcohol before and during the urine collection.

Tell the person doing the test if you are pregnant[8].

Do not exercise before this test[8].

How is the test done?

A sample of blood and urine may be collected for this test.

Venous blood:

When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.

24 hour urine collection:

For a 24-hour urine collection, all of the urine that you pass over a 24-hour time period must be collected. If you are in the hospital, a healthcare worker will collect your urine. You will receive a special container to collect the sample in if you are doing the collection at home. The following are directions for collecting a 24-hour urine sample while at home:

  • In the morning scheduled to begin the urine collection, urinate in the toilet and flush away the first urine you pass. Write down the date and time. That is the start date and time for the collection.

  • Collect all urine you pass, day and night, for 24 hours. Use the container given to you to collect the urine. Avoid using other containers. The urine sample must include the last urine that you pass 24 hours after starting the collection. Do not allow toilet paper, stool, or anything else to be added to the urine sample.

  • Write down the date and time that the last sample is collected.

  • The urine sample may need to be kept cool during the 24-hour collection period. If so, keep the closed container in a pan on ice. Do not put ice in the container with the urine.

How will the test feel?

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

Venous blood:

During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.

24 hour urine collection:

This test usually causes no discomfort.

What should I do after the test?

Venous blood:

After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.

24 hour urine collection:

When 24-hour urine collection is complete, close the container and seal the lid tightly. Return the sample in the urine container to the facility or healthcare worker as instructed. If you had the sample in an ice bath, return the sample within two hours after removing the container from the ice bath.

What are the risks?

Blood: During a blood draw, a hematoma (blood-filled bump under the skin) or slight bleeding from the puncture site may occur. After a blood draw, a bruise or infection may occur at the puncture site. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this test.

Urine: A urine test is generally considered safe. Talk to your healthcare worker if you have questions or concerns about this test.

What are normal results for this test?

Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following are considered to be normal results for this test:

  • Males (20 to 29 years): 94-140 mL/min/1.73 m2 (0.91-1.35 mL/s/m2) [2]
  • Females (20 to 29 years): 72-110 mL/min/1.73 m2 (0.69-1.06 mL/s/m2) [2]
  • Males (30 to 39 years): 59-137 mL/min/1.73 m2 (0.57-1.32 mL/s/m2) [2]
  • Females (30 to 39 years): 71-121 mL/min/1.73 m2 (0.68-1.17 mL/s/m2) [2]
  • Note: For each decade after the fourth decade in both sexes, values decrease approximately 6.5 mL/min based on 1.73 m2 body surface (0.06 mL/s per m2) [2]
  • Infant (0 to 1 year): 72 mL/min/1.73 m2 (0.69 mL/s/m2) [2]
  • Infant (1 year): 45 mL/min/1.73 m2 (0.43 mL/s/m2) [2]
  • Infant (2 years): 55 mL/min/1.73 m2 (0.53 mL/s/m2) [2]
  • Children (3 years): 60 mL/min/1.73 m2 (0.58 mL/s/m2) [2]
  • Children (4 years): 71 mL/min/1.73 m2 (0.68 mL/s/m2) [2]
  • Children (5 years): 73 mL/min/1.73 m2 (0.70 mL/s/m2) [2]
  • Children (6 years): 64 mL/min/1.73 m2 (0.62 mL/s/m2) [2]
  • Children (7 years): 67 mL/min/1.73 m2 (0.65 mL/s/m2) [2]
  • Children (8 years): 72 mL/min/1.73 m2 (0.69 mL/s/m2) [2]
  • Children (9 years): 83 mL/min/1.73 m2 (0.80 mL/s/m2) [2]
  • Children (10 years): 89 mL/min/1.73 m2 (0.86 mL/s/m2) [2]
  • Children (11 years): 92 mL/min/1.73 m2 (0.89 mL/s/m2) [2]
  • Children (12 years): 109 mL/min/1.73 m2 (1.05 mL/s/m2) [2]
  • Children (13 to 14 years): 86 mL/min/1.73 m2 (0.83 mL/s/m2) [2]

What might affect my test results?

  • Results decreased in:
    • Advanced age (ie, greater than 80 years) [9]
      • GFR can decrease at a rate of 13 mL/decade after ages 45 to 50 years [8]
    • Acute and chronic renal failure [1]
    • Inadequate urine flow rate (ie, due to dehydration or incomplete voiding) [10].
    • Exercise [8]
    • Muscle wasting [9]
  • Results increased in:
    • Creatinine clearance can overestimate GFR by 10% to 20% at all levels of renal function [8]
    • Pregnancy (rises rapidly in early pregnancy and remains elevated until term; returns to normal quickly following delivery) [8]
  • Other:
    • Gender (males have higher GFR, as compared to females) [8]
    • Diet can influence renal function [8]
    • Diurnal variation (ie, GFR typically lower at night and highest in late morning) [8]

What follow up should I do after this test?

Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.

Where can I get more information?

Related Companies

References

  1. Nicoll D, McPhee SJ, Pignone M, et al (Eds): Pocket Guide to Diagnostic Tests, 3rd. McGraw-Hill, New York, NY, United States, 2001.
  2. Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.
  3. Wortmann RL: Management of hyperuricemia. In: Koopman WJ (Ed): Arthritis and Allied Conditions, 14. Williams and Wilkins, Baltimore, 2001, pp 2073-84.
  4. Kramer H & Molitch ME: Screening for kidney disease in adults with diabetes. Diabetes Care 2005; 28:1813-1816.
  5. Segura J, Campo C, & Gil P: Development of chronic kidney disease and cardiovascular prognosis in essential hypertensive patients. J Am Soc Nephrol 2004; 15:1616-1622.
  6. Steinke JM, Sinaiko AR, Kramer MS, et al: The early natural history of nephropathy in type 1 diabetes. Diabetes 2005; 54:2164-2171.
  7. Knobler H, Zornitzki T, Vered S, et al: Reduced glomerular filtration rate in asymptomatic diabetic patients: predictor of increased risk for cardiac events independent of albuminuria. J Am Coll Cardiol 2004; 44(11):2142-2148.
  8. Duarte CG & Preuss HG: Assessment of renal function--glomerular and tubular. Clin Lab Med 1993; 13(1):33-52.
  9. Rimon E, Kagansky N, Cojocaru L, et al: Can creatinine clearance be accurately predicted by formulae in octogenarian in-patients. QJM 2004; 97(5):281-287.
  10. Haycock GB `: Old and new tests of renal function. J Clin Pathol 1981; 34(11):1276-1281.

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