| Introduction |
The kidneys filter creatinine, a byproduct of the breakdown of phosphocreatine, with just a tiny amount being actively released. Although there is some tubular reabsorption of creatinine, there is an almost comparable amount of tubular secretion. Any variations in blood creatinine levels indicate renal function since they are connected to excretion. The active secretion of creatinine, which makes up a higher portion of the total creatinine cleared, will cause creatinine clearance to be overstated in situations of severe renal failure. Dehydration may be indicated by elevated levels of blood urea nitrogen (BUN) and creatinine.
Tests for creatinine are used to determine the amount of a waste substance called creatinine in your blood and urine. Labs can use creatinine as a marker to determine how well your kidneys are operating since it is created during the regular breakdown of muscle tissue and does so at a pretty constant pace. The screening, diagnosis, and monitoring of kidney (renal) problems, such as chronic kidney disease and acute renal failure, are done using creatinine testing. They can also be used to assess how other illnesses, such those of the heart and liver, affect the kidneys.
| Purpose of Test |
If your symptoms are troubling, a doctor may prescribe a creatinine test to help diagnose or rule out renal disease. The tests may also be performed to determine whether another illness, such as heart failure, or medicinal intervention is harming your kidneys (such as exposure to certain chemotherapy drugs). Creatinine tests may also be used to assess your response to kidney treatment or to check that your kidneys are healthy prior to surgery.
One of the first tests a doctor will perform to assess kidney function is a creatinine test. They are quick, simple to use, and reasonably priced to complete. They may be utilized for both a standard physical exam and the diagnosis and treatment of diseases.
| How the Test Works |
Creatinine is continually produced by the body as part of normal bodily processes. It is produced when the chemical creatine, which is largely present in muscles, is transformed into energy. A byproduct of such procedure is creatinine.If your kidneys are healthy, creatinine will be eliminated from your body through urine. Creatinine cannot be eliminated as efficiently if the kidneys are damaged, and it will start to build up in the circulation.
The levels of creatinine in your blood and urine are assessed using two distinct tests:
A blood test called serum creatinine (SCr) can be used to determine how much creatinine is present in the circulation. Any rises over the predicted range can be taken as a reliable sign of renal impairment since the rate of production and excretion is essentially constant.
A urine test called creatinine clearance (CrCl) compares the SCr with the total quantity of creatinine expelled in urine over the course of 24 hours.
The estimated glomerular filtration rate may then be determined using serum creatinine data (eGFR). The efficiency of the kidney's filters is assessed using an algorithm that considers age, sex, race, height, and weight. Low serum creatinine output numbers may indicate probable renal impairment. The estimated glomerular filtration rate (eGFR) measures the amount of blood that passes through kidney filters once per minute. People with greater muscle would have higher SCr readings. Similar to how exercise causes more creatine to be turned into energy, intense physical activity can change both SCr and CrCl levels.
| Indications for Testing |
The basic metabolic panel (BMP), a common battery of tests that also includes albumin, blood urea nitrogen (BUN), calcium, electrolytes (sodium, potassium, chloride, and bicarbonate), glucose, and phosphorus, contains serum creatinine. The BMP can be used to test for renal disorders or to aid in their diagnosis.The older method, creatinine clearance, which required 24-hour urine collection, has mostly been replaced by the more recent algorithm, the eGFR, which just needs the SCr. Despite this, creatinine clearance is still often utilized for diagnosis, particularly when a 24-hour urine volume test is required for a more thorough analysis. If you have very big muscle mass or a noticeable decline in muscle mass, the test may offer more accurate information.
| Conditions it Helps Diagnose |
Any variety of kidney problems, which are generally categorized as either chronic renal disease or an acute kidney injury, can be diagnosed with the use of creatinine testing.
Renal function impairment that is gradual and irreversible is known as chronic kidney disease (CKD). It can also be brought on by other disorders such as lupus, polycystic kidney disease (PKD), and recurrent kidney infections, among others. In certain circumstances, CKD can progress to end-stage renal disease (ESRD), which necessitates dialysis or a kidney transplant in order to avoid death.
Acute kidney injury (AKI) is a term used to describe any disorder that damages and impairs the kidneys. An AKI can occasionally be reversed, unlike CKD. An injury or condition that occurs before, in, or after the kidneys (prerenal), kidneys (renal), or both may be the cause of an AKI (postrenal)..
Among the examples:
Dehydration, heart attacks, severe organ failure, sepsis, considerable blood loss, and the excessive use of NSAIDs are a few prerenal causes.
Among the causes of kidney disease include kidney cancer, renal damage, severe kidney infections, medication allergies, and vasculitis.
Kidney stones, obstructions in the ureters, urine retention, urologic malignancy (such as bladder cancer or prostate cancer), and any ailment that might compress a ureter from the outside are examples of postrenal causes.
Acute renal failure that results from an AKI can also be prevented or cured after the underlying injury or condition is addressed.
| Before the Test |
For a serum creatinine blood test, no preparations are required. Contrarily, you might need to avoid taking some drugs or engaging in certain activities if the 24-hour urine collection could affect the results.
Timing of Blood Test
The serum creatinine blood test can be done at any time of day. Planning is required if a creatinine clearance urine test is done in addition to a serum creatinine measurement.
Timing of Urine Test
You must pick up a specific container from the lab to bring home in order to do a creatinine clearance pee test. You are required to return the container as soon as you can the next day once the urine collection is finished.You must present your ID and personal information when picking up the collection kit from the lab so that a label with a generated code may be printed and adhered to the collection container. In order to expeditiously deliver the sample to the lab, your insurance or payment information can also be requested. In order to avoid having to move the container from one location to another, it is frequently ideal to complete the 24-hour urine collection on your day off. For students, you might choose to begin the collection on a Sunday and deliver the sample to the lab on Monday.
Location
The blood tests can be carried out in a doctor's office, clinic, hospital, or unaffiliated lab. A scheduled appointment is not necessary at all walk-in clinics. The collection of the urine is done at home. To keep the sample cold, you will need a cool location, such as a refrigerator or a transportable ice chest.
What to Wear
Wear short sleeves or a shirt with readily rollable sleeves for the serum creatinine blood sample.
Food and Drink
For either test, dietary restrictions are often not necessary. You could be requested to abstain from drinking the day before the test and throughout the 24-hour urine collection, though. You could also be told to stay away from intense activity because it can harm your outcomes.
Medications
For a serum creatinine blood test, you typically do not need to stop taking your prescriptions, but for the 24-hour urine collection, you might be recommended to. This is so that the urine test can accurately depict how your kidneys work without interference from any chemicals that can affect filtration. As a result, it's crucial to let your doctor know about any medications you're taking, whether they're prescription, over-the-counter, dietary, conventional, or recreational.
Problematic drugs may include:
Antacids like Tagamet (cimetidine)
Antibiotics like Bactrim (trimethoprim-sulfamethoxazole)
Anticonvulsants like Phenurone (phenacemide)
Calcitriol (biologically active vitamin D)
Corticosteroids
Salicylates, including aspirin
With that being said, never stop taking any medication without first speaking with a healthcare provider.
What to Bring
Be sure to bring your ID and health insurance cards with you when signing in at the lab.
| During the Test |
You may either collect the pee first and then have the blood test done when you drop off the sample, or you can do it the other way around.
Blood Test
Pre-Test: You will be led to an examination room on the day of the test after signing in and verifying your insurance information. There, your height and weight will be noted. Your body mass index (BMI) will then be determined using this information for the eGFR. Your age, sex, and ethnicity will also be taken into account in the analysis and confirmed.
Throughout the Test: The blood draw, done by a phlebotomist, is performed as follows：
1. You'll be requested to roll up your sleeves after being seated in a chair with an elevated armrest. Which arm has the fuller vein will frequently be checked by the phlebotomist.
2. To help the vein enlarge, a tourniquet made of elastic band is wrapped around your upper arm.
3.If your veins are narrow, blood may be obtained from your wrist instead of the median cubital vein in the crook of your arm.
4. An antiseptic swab is then used to clean the skin.
5. The vein is carefully poked with a needle. You might experience a little pressure or pain. If there is any severe pain, let the phlebotomist know.
6. A test tube with a vacuum seal is filled with about 3 mL of blood.
7. The tourniquet is then taken off after the needle.
8. Your arm is bandaged, and the pathologist examines the sample that was sent.
Post-Test: You will be free to go unless you feel lightheaded from the blood draw, in which case you may be asked to rest until you feel well.
24-Hour Urine Collection
Pre-Test: Assemble the lab-provided collection materials. A little plastic collection cup and one or more sizable containers with detachable lids that may or may not include preservatives are required. A preprinted form should be available for you to use to record the time and date of each urine. The 24-hour collection won't start until the morning unless a medical professional specifically states differently. It's critical to keep in mind that you cannot miss a sample because the urine volume influences the calculations for the CrCl and eGFR just as much as the creatinine content does.
Throughout the Test: To collection procedure can vary slightly but generally involves the same basic steps.
1. You won't save the urine from your first urinal when you wake up in the morning. While recording the date and time, flush the first specimen. Your starting time is now.
2.For the following 24 hours, use the plastic collection cup to collect all the pee you pass. A paper or glass cup may also be used, but not a metal one.
3. Fill the collecting container with the lid after each pee. Each time you use the collecting cup, rinse it. If you use a paper cup, discard it after just one usage.
4.Unless otherwise indicated, keep the urine in the fridge or an ice chest.
5. Note the time that each urine occurs.
6.To finish the process, try to urinate at the same time the next day, 24 hours after the start time.
7.If you can't, that's OK. Record the final (stop) time and date.
Post-Test: The sealed containers must be delivered to the lab as soon as feasible after the collection procedure is finished. Call the lab for instructions if you are running late for any reason.
| After the Test |
You can experience localized swelling or bruising at the location of the puncture after the serum creatinine blood draw. Call your doctor right away if you have severe discomfort or exhibit any signs of an infection, such as a fever, shivering, a quick heartbeat, or rapid breathing. However, infection is not prevalent. After a 24-hour urine collection, there is no extra maintenance required. You can resume taking any drugs you stopped taking and resume your regular daily activities unless a healthcare professional instructs you otherwise.
| Interpreting the Results |
The results of the creatinine tests can provide a very strong indication of how well your kidneys are functioning. The results are classified based on a reference range (RR) which delineates the range of numeric values considered normal for that test.Anything above the upper end of the RR is considered abnormally high (often described on the report with the letter "H"). Similarly, anything below the lower end of the RR is considered abnormally low (described with the letter "L").
The normal ranges for a serum creatinine (SCr) test are:
0.5 to 1.1. milligrams (mg) per deciliter (dL) in women
0.6 to 1.3 mg/dL in men
0.5 to 1.0 mg/dL for children ages 3 to 18 years
0.3 to 0.7 mg/dL for children under 3
The normal ranges for a creatinine clearance (CrCl) test are:
87 to 107 mL/minute for women
107 to 139 mL/minute for men
The CrCl range in children is not so straightforward. It relies on one of several different algorithms that calculate the CrCl based on age, weight, height, and SCr. As a baseline, newborns are expected to have a CrCl of 40 to 64 mL/minute.Normal value ranges may vary slightly among different labs. Some use different algorithms or test different samples. As such, you should try to use the same lab whenever monitoring kidney function to ensure accurate comparative results.