Kidney function tests





Definition

Kidney function tests is a collective term for a variety of individual tests and procedures that can be done to evaluate how well the kidneys are functioning. A doctor who orders kidney function tests and uses the results to assess the functioning of the kidneys is called a nephrologist.


Purpose

The kidneys, the body's natural filtration system, perform many vital functions, including removing metabolic waste products from the bloodstream, regulating the body's water balance, and maintaining the pH (acidity/alkalinity) of the body's fluids. Approximately one and a half quarts of blood per minute are circulated through the kidneys, where waste chemicals are filtered out and eliminated from the body (along with excess water) in the form of urine. Kidney function tests help to determine if the kidneys are performing their tasks adequately.


Precautions

The doctor should take a complete history prior to conducting kidney function tests to evaluate the patient's food and drug intake. A wide variety of prescription and over-the-counter medications can affect blood and urine kidney function test results, as can some food and beverages.

Description

Many conditions can affect the ability of the kidneys to carry out their vital functions. Some conditions can lead to a rapid (acute) decline in kidney function; others lead to a gradual (chronic) decline in function. Both can result in a build-up of toxic waste substances in the blood. A number of clinical laboratory tests that measure the levels of substances normally regulated by the kidneys can help to determine the cause and extent of kidney dysfunction. Urine and blood samples are used for these tests.

The nephrologist uses these results in a number of ways. Once a diagnosis is made that kidney disease is present and what kind of kidney disease is causing the problem, the nephrologist may recommend a specific treatment. Although there is no specific drug therapy that will prevent the progression of kidney disease, the doctor will make recommendations for treatment to slow the disease as much as possible. For instance, the doctor might prescribe blood pressure medications, or treatments for patients with diabetes. If kidney disease is getting worse, the nephrologist may discuss hemodialysis (blood cleansing by removal of excess fluid, minerals, and wastes) or kidney transplantation (surgical procedure to implant a healthy kidney into a patient with kidney disease or kidney failure) with the patient.


Laboratory tests

There are a number of urine tests that can be used to assess kidney function. A simple, inexpensive screening test—a routine urinalysis—is often the first test conducted if kidney problems are suspected. A small, randomly collected urine sample is examined physically for things like color, odor, appearance, and concentration (specific gravity); chemically, for substances such a protein, glucose, and pH (acidity/alkalinity); and microscopically for the presence of cellular elements (red blood cells [RBCs], white blood cells [WBCs], and epithelial cells), bacteria, crystals, and casts (structures formed by the deposit of protein, cells, and other substances in the kidneys's tubules). If results indicate a possibility of disease or impaired kidney function, one or more of the following additional tests is usually performed to pinpoint the cause and the level of decline in kidney function.

  • Creatinine clearance test. This test evaluates how efficiently the kidneys clear a substance called creatinine from the blood. Creatinine, a waste product of muscle energy metabolism, is produced at a constant rate that is proportional to the individual's muscle mass. Because the body does not recycle it, all creatinine filtered by the kidneys in a given amount of time is excreted in the urine, making creatinine clearance a very specific measurement of kidney function. The test is performed on a timed urine specimen—a cumulative sample collected over a two to 24-hour period. Determination of the blood creatinine level is also required to calculate the urine clearance.
  • Urea clearance test. Urea is a waste product that is created by protein metabolism and excreted in the urine. The urea clearance test requires a blood sample to measure the amount of urea in the bloodstream and two urine specimens, collected one hour apart, to determine the amount of urea that is filtered, or cleared, by the kidneys into the urine.
  • Urine osmolality test. Urine osmolality is a measurement of the number of dissolved particles in urine. It is a more precise measurement than specific gravity for evaluating the ability of the kidneys to concentrate or dilute the urine. Kidneys that are functioning normally will excrete more water into the urine as fluid intake is increased, diluting the urine. If fluid intake is decreased, the kidneys excrete less water and the urine becomes more concentrated. The test may be done on a urine sample collected first thing in the morning, on multiple timed samples, or on a cumulative sample collected over a 24-hour period. The patient will typically be prescribed a high-protein diet for several days before the test and be asked to drink no fluids the night before the test.
  • Urine protein test. Healthy kidneys filter all proteins from the bloodstream and then reabsorb them, allowing no protein, or only slight amounts of protein, into the urine. The persistent presence of significant amounts of protein in the urine, then, is an important indicator of kidney disease. A positive screening test for protein (included in a routine urinalysis ) on a random urine sample is usually followed up with a test on a 24-hour urine sample that more precisely measures the quantity of protein.

There are also several blood tests that can aid in evaluating kidney function. These include:

  • Blood urea nitrogen test (BUN). Urea is a byproduct of protein metabolism. Formed in the liver, this waste product is then filtered from the blood and excreted in the urine by the kidneys. The BUN test measures the amount of nitrogen contained in the urea. High BUN levels can indicate kidney dysfunction, but because BUN is also affected by protein intake and liver function, the test is usually done together with a blood creatinine, a more specific indicator of kidney function.
  • Creatinine test. This test measures blood levels of creatinine, a by-product of muscle energy metabolism that, similar to urea, is filtered from the blood by the kidneys and excreted into the urine. Production of creatinine depends on an person's muscle mass, which usually fluctuates very little. With normal kidney function, then, the amount of creatinine in the blood remains relatively constant and normal. For this reason, and because creatinine is affected very little by liver function, an elevated blood creatinine level is a more sensitive indicator of impaired kidney function than the BUN.
  • Other blood tests. Measurement of the blood levels of other elements regulated in part by the kidneys can also be useful in evaluating kidney function. These include sodium, potassium, chloride, bicarbonate, calcium, magnesium, phosphorus, protein, uric acid, and glucose.

Results

Normal values for many tests are determined by the patient's age and gender. Reference values can also vary by laboratory, but are generally within the following ranges:


Urine tests

  • Creatinine clearance. For a 24-hour urine collection, normal results are 90 mL/min–139 mL/min for adult males younger than 40, and 80–125 mL/min for adult females younger than 40. For people over 40, values decrease by 6.5 mL/min for each decade of life.
  • Urine osmolality. With restricted fluid intake (concentration testing), osmolality should be greater than 800 mOsm/kg of water. With increased fluid intake (dilution testing), osmolality should be less than 100 mOSm/kg in at least one of the specimens collected. A 24-hour urine osmolality should average 300–900 mOsm/kg. A random urine osmolality should average 500–800 mOsm/kg.
  • Urine protein. A 24-hour urine collection should contain no more than 150 mg of protein.
  • Urine sodium. A 24-hour urine sodium should be within 75–200 mmol/day.

Blood tests

  • Blood urea nitrogen (BUN) should average 8–20 mg/dL.
  • Creatinine should be 0.8–1.2 mg/dL for males, and 0.6–0.9 mg/dL for females.
  • Uric acid levels for males should be 3.5–7.2 mg/dL and for females 2.6–6.0 mg/dL.

Low clearance values for creatinine indicate a diminished ability of the kidneys to filter waste products from the blood and excrete them in the urine. As clearance levels decrease, blood levels of creatinine, urea, and uric acid increase. Because it can be affected by other factors, an elevated BUN, alone, is suggestive, but not diagnostic for kidney dysfunction. An abnormally elevated plasma creatinine is a more specific indicator of kidney disease than is BUN.

Low clearance values for creatinine and urea indicate a diminished ability of the kidneys to filter these waste products from the blood and to excrete them in the urine. As clearance levels decrease, blood levels of creatinine and urea nitrogen increase. Since it can be affected by other factors, an elevated BUN alone is certainly suggestive for kidney dysfunction. However, it is not diagnostic. An abnormally elevated blood creatinine, a more specific and sensitive indicator of kidney disease than the BUN, is diagnostic of impaired kidney function.

The inability of the kidneys to concentrate the urine in response to restricted fluid intake, or to dilute the urine in response to increased fluid intake during osmolality testing, may indicate decreased kidney function. Because the kidneys normally excrete almost no protein in the urine, its persistent presence, in amounts that exceed the normal 24-hour urine value, usually indicates some type of kidney disease.


Patient education

Some kidney problems are the result of another disease process, such as diabetes or hypertension. Doctors should take the time to inform patients about how their disease or its treatment will affect kidney function, as well as the different measures patients can take to help prevent these changes.


Resources

BOOKS

Brenner, Barry M. and Floyd C. Rector Jr., eds. The Kidney, 6th Edition. Philadelphia, PA: W. B. Saunders Company, 1999.

Burtis, Carl A. and Edward R. Ashwood. Tietz Textbook of Clinical Chemistry. Philadelphia, PA: W.B. Saunders Company, 1999.

Henry, J. B. Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia, PA: W. B. Saunders Company, 2001.

Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis, MO: Mosby, Inc., 1998.

Wallach, Jacques. Interpretation of Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams & Wilkens, 2000.


ORGANIZATIONS

National Kidney Foundation (NKF). 30 East 33rd Street, New York, NY 10016. (800)622-9020. http://www.kidney.org .

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). National Institutes of Health, Building 31, Room 9A04, 31 Center Drive, MSC 2560, Bethesda, MD 208792-2560. (301) 496-3583. http://www.niddk.nih.gov/health/kidney/kidney.htm .

OTHER

National Institutes of Health. [cited April 5, 2003]. http://www.nlm.nih.gov/medlineplus/encyclopedia.html .

National Institutes of Health. [cited June 29, 2003] <http://www.nlm.nih.gov/medlineplus/ency/article/003005.htm ; .


Paula Ann Ford-Martin
Mark A. Best, M.D.



User Contributions:

osama
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Apr 23, 2006 @ 3:15 pm
How we calculate urine osmolality . what is the equation?
Anuj
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Jun 2, 2006 @ 2:02 am
Simple and informative from a paients perspective. wish there were also some precautionary measures for patients listed as well. Thanks
Muffaddal
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Jul 23, 2007 @ 3:03 am
my kid had puj obstruction. doc's sugested pyloplasty and that has been done.. the renogram result before operation was showing impared fucntion as 25% - 75% later for a followup test it showed 21% - 79% and lastly after 1 year the renal test was done and it showed 19 and 81.. what treatment would be recommended

thxn
Aga chimaobi
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Nov 3, 2007 @ 6:06 am
kidney problem has been a mproblem in many countries and we should have more nephrologist in mary parts of the world and also educate people more about the desease,
thanks
Robert
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Jan 25, 2008 @ 8:08 am
I have a blood creatinine level of 1.7. I am scheduled for hernia surgery. Any problems I need to be aware of?
Dingha sama
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Apr 21, 2008 @ 12:12 pm
.I just wish to appriciate this work and to enquire if there are any journals on the relationship setween creat leveland diabetes.Thanks
zerihun
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Oct 3, 2008 @ 2:02 am
I AM VERY INTERESTED BY THE INFORMATION YOU GAVE ABOUT KIDNEY FUNCTION TESTS. IN THE FUTURE, I HOPE YOU WILL PROVIDE ME WITH MORE UPDATED INFORMATION.

THANK YOU
Ahamandi
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Apr 18, 2009 @ 2:14 pm
i got this nephritis almost from 5 years & i hope for c cure.i know there is one ,cause there is cure for each disease in this world.GOD gave each problem with cure,time is the challenge.dear friends i hope each & everyone in this world who has a problem to be cured from it.i am very very patient with mine,forbiding my self from the most dilicious food only 2 protect my kidneys.hope all the patients get well(regards from the lovliest weather on planet - Lebanon - beirut) salam
G Srinivasa Rao
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Aug 18, 2009 @ 7:07 am
I have some kidney probs. The blood creatine level has gone up to 6. Doctor has suggested not to take any protine food. And I am following the same. Will I required to go for dialysis. For going for dialysis minimum what creatine level has to be there ?

Kindly reply.
Saleh
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Jan 1, 2010 @ 2:14 pm
I Thank you to all very important information you gave
I like to know the roll of electrolytes in the kidney function
thank you
Saurabh Dangre
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Jan 11, 2010 @ 9:21 pm
My father is having Kidney disease.
He is on regular dialysis(twice a week),
we are taking aayrvedic and homeopathic treatment..
But, now his serum creatinine level is increase from 8 to 12.20.
plz suggest the treatment and diet for control the same
plz guide me
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Apr 3, 2010 @ 8:20 pm
Very good explanation. I would like to cite this page in my paper. There is no date it was written. I can not use it in my paper.
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Apr 5, 2010 @ 2:02 am
I'm a medical student.I have a brother who is 45 years old feeling pain at the ioin region for one month specially when he bend his body. He is patient of hypertension and he takes antihypertensive drugs regularly.Recently he has done serum creatinine test and the value was 1.35gm/dl.Is it indicate kidney disiease? Which test he sholud do further?
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May 12, 2010 @ 5:05 am
What do the letters and word Alb/Creat ratio mean in my Renal Function tests please.also the letters eGFR mean.
many thanks

Helyn
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Sep 24, 2010 @ 8:08 am
Does microscopic blood add to the level of protein that is reported on a 24 hr urine protein test?
Thanks for the help.
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Sep 27, 2010 @ 10:10 am
what are the conditions affecting the function of the kidneys??
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Oct 20, 2010 @ 10:22 pm
Dear sir/ mdm

If my urine found a layer kind of syrub at the bottom of the bottle.
Does it mean I have kidney problem? My left back ard the waist sometime
can feel ached when I sit. Is it a sign of kidney problem?
Please kindly advise what I should do!
Thank you for your kind attention!

Best Regards
Joselyn
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Oct 25, 2010 @ 3:03 am
from india
my blood test result-
Urea-22
cratinine- 1.07

Please tell me the condition of my kidney.

Thank you
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Nov 10, 2010 @ 3:03 am
I have atrial fibrillation and take digoxin, warfarin, lisinopril and metoprolol. About a year ago I started to experience infrequent, sharp and sudden chest pains. The pains last only a few seconds. I am 45 years old, so I thought maybe I had a plaque build up on my arteries. I did some research and due to not having health insurance, I wanted to take a natural approach for this problem, which I thought was plaque/calcium build up. I eat a very generous amount of raw fruits and vegetables, including pomegranate concentrate, which I have been taking for about a year. Approximately two months ago I started taking 1250 mg. of EDTA along with 1000 mg. of L-Arginine a day. Less than a week ago I had some blood work done and the next day the nurse called and informed me, I need to get to the nearest emergency room because my potassium serum level is dangerously high. She wouldn't tell me over the phone what the results are. I did some research and looked into symptoms and possible causes and it seems the underlying cause could be a kidney dysfunction. I don't have any of the severe high potassium level symptoms, but I was having some about a week prior to the test. Without going into detail I believe my system got overloaded with a few toxins I was exposed to. In addition, I have herpes and just two days ago I have broken out again, perhaps due to worrying and stress. I never did go to the emergency room, but I significantly reduced my potassuim intake. I feel much better and don't have any of the symptoms I had a week prior to the blood test. I also slowed my chelation theraphy down to 625 mg. every 4 to 5 days. Any ideas on what could have been the cause of my apparent high potassium level? And since I am not having any diffculty urinating, and as I increase my water intake my urine is clearer, which is to assume my kidney function must not be severly impaired, if impaired at all, therefore did my potassium level decrease, and is it possible or as cells die and I eat more food with potassium, does it mean it will only go up, not down?
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Nov 24, 2010 @ 6:06 am
THIS STUFF IS AWESOME.I THINK THE WRITER OF THIS ARTICLE DID QUITE WELL IN THE RESEARCH AND THE RESULT HAS A GREAT IMPACT.
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Dec 7, 2010 @ 3:03 am
what is the significance of performing various serum & blood biochemical parameters??
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Jan 14, 2011 @ 9:09 am
My father is having Kidney disease.
now his serum creatinine level is 3.5
plz suggest the treatment and diet for control the same
plz guide me
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Feb 17, 2011 @ 8:08 am
Freguent urination during night or when cold.
I wake up 3-4 time at night. What is the cause? How to decrease the frequency?
christine
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Feb 17, 2011 @ 9:09 am
I found this about kidney function it seems to explain it very well.
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Feb 17, 2011 @ 2:14 pm
thank you for answer me about quation, can you tell me the equation of esstimation (24 hr. protein in urine collection )plz.
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Feb 23, 2011 @ 8:08 am
iam 19 year old boy living in delhi i have the problem of kidney failure .i go for dialysis twice a weak please tell me some solution for this.
Karen
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Jul 4, 2011 @ 10:10 am
I recently got a blood test done and it came back showing UREA at 7.2. I am female aged 45. What does this mean and what can I do to get it lower or is that possible?
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Sep 5, 2011 @ 7:07 am
HELLO;
MY MOTHER is suffering from high creatinine and uric acid,creatinine is about 12.4 and uric acid is 157.
her gfr is 19mil/min...
so please tell me the easy way for her treatment, she didn't want to do dialysis...can she improve her disease with medicines.i am very thankful t you please tell me soon.
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Sep 6, 2011 @ 4:04 am
i m getting heavy pain at kidney portion.i did sonograpy urine nd blood test also but still m getting little pain.plz give me some solution for that.thank u.
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Sep 10, 2011 @ 10:22 pm
info for the kidney function test for your perusal alos for the next 24 hours it will take tototo ccl bbhytrv
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Sep 23, 2011 @ 2:14 pm
what is the name of the test that mussures amount of bicarbonate?
Thank you
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Oct 2, 2011 @ 4:04 am
just a question about the kidney levels what if normal is level is at 3 what is at 4 and what does it mean for a male.

thank you very much
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Oct 20, 2011 @ 3:15 pm
what is the problem if that dog blood report come? blood urea nitrogen 26 and serum creatinine 18
romy
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Nov 30, 2011 @ 10:10 am
my father's serum cretenine level is 4.3 .please suggest me weather it can be cured by medicine and by proper diet or he should go for dylasis.
swathi
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Dec 6, 2011 @ 11:23 pm
My fatehr's serum cretenine level is 2.94. please suggest me is there any treatment which can be curred by only medicines he is diabetic & High BP.he is taking treament for that for one week but is serum level is not comming doem is this is an seriuos problem. what is diet he has to take pls suggest me.
Kevin
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Jan 17, 2012 @ 9:09 am
My dad recently got test results back from kidney doctor. Doctor said one result went from 1.45 from test done 6 months ago to 1.7 now. And this was not good...values going in wrong direction. I cannot remember what this test was or how serious a 1.7 was (although doctor seemed concerned). Do you know what this test may have been for? Thanks.
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Feb 15, 2012 @ 11:23 pm
i have high 47 value of urea in my blood analysis , is something fishy?

sudesh khokAR
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May 7, 2012 @ 9:09 am
hi friends
The normal Creatinine TEST RESULTS should be min - 0.6, max 1.5( NORMAL HUMAN BODY )
my father having a kidney problem... today his test result have increased from 1.8 to 3.04..
really .. i was shocked by seeing this ...
I DONT KNOW WHAT THE REASON ..

I HOPE THIS WILL REDUCE TO AS 1.8..

can any one suggest any measures to be taken.. about the the food .. what is the best food menu to control this .. ANY SUGGESSIONS PLZ SEND IT TO MY MAIL ID ..
abhay
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May 29, 2012 @ 6:06 am
If report show 1.7 & diabitic patient what is liquid intake limit in ml.,

& type of food intake
Aki
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May 29, 2012 @ 10:10 am
What if diabetic patient having creatinine report
1.7 ? What food can be taken & is there any liquid intake
Limitation in ml.
serene
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Jun 7, 2012 @ 5:05 am
Hi evryone
My name is serene, am from canada. My husband has been sick for the past 11yrs now and the doctor demand that my husband needs surgery, that his kidney is bad and he need a kidney transplant. so just 2weeks ago a family relation introduce a female spell caster online (priestessmunak@gmail.com) to that did a spell for my husband's health. she casted the spell and also sent a potion and a soap for my husband to bath with for 3good days.
The greatest miracle that happened was my husband wakeup on the 3rd day morning very bright and he said he is feeling different and strong.
when we went for checkup, the doctor was surprised and was asking several questions.
right now as i write, my husband is well and health just as the Priestess Munak has mention.
I cant thank her enough for restoring my husband's health and bringing our family together.
Godbless you priestess munak.
I would also want you to meet her just as i did with faith on priestessmunak@gmail.com.

Regards.
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Jul 5, 2012 @ 6:18 pm
My 88 years old father's blood test result-

BUN:=23
Creatonin= 1.7
Potassium =4

Could you please tell me the condition of his kidney. How dangerous it is?

Thank you in advance,
Irina
nany
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Jul 14, 2012 @ 4:04 am
hi i am nany from india , my mother is sick from last many years.now the doctor declair her an an orthropores patient.after taking lots of medicens now she did some tests & reports shows high creatinine level=1.19 ;uric acid=4.60 and protein=7.84 which is higher than normal rang.
could u please tell me the condition of his kidney. how dangerous it is
mary
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Jul 23, 2012 @ 4:04 am
I am very greateful for the informative content of this article.
jeanne
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Aug 8, 2012 @ 3:15 pm
my mother in laws test results are cr493 and urea 9803 help please
amit kumarc das
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Aug 14, 2012 @ 12:12 pm
hi,my problem, 24 hour urine protein test result 1100mg.cretin=.7
so,please help me.
Rick
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Oct 16, 2012 @ 3:03 am
My clinic called with my blood and urine results concerning my kidney disease. Their numbers don't come close to matching anything I've found on the Internet. Maybe someone can help? Here's what they told me:

Microalbumin: Normal 0-17, Mine is 27

Creatinin 1: Normal 22-32, Mine is 40.1

Creatinin 2: Normal 0-30, Mine is 67.3

Nurse didn't explain difference in the two Creatinin tests. If anyone can make sense of this, please let me know. Thanks.
anu
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Oct 20, 2012 @ 10:10 am
hello,
my aunt test results ain't good ,creatinin was coming out to be 23.
Dialysis is recommended.Please help me out.Thanks
melese
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Dec 10, 2012 @ 6:06 am
NICE DOCTORS EXPLANATION!!! CAN I HAVE PPT DOCUMENT OF IT? I AM MEDICAL STUDENT PLEASE HELP ME?
rodah
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Dec 21, 2013 @ 1:01 am
out of ten symptoms of kidney disease given seven are experienced on my body plz advice me
salman
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Jun 27, 2014 @ 7:07 am
hi its salman here well i just asking to u dr sir my mother blood test is not well coz her blood ure is 142mgl please in this type of case what we do. becouse sir her potasiam test is hight please you guide me what we do thanx..
ranvir
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Sep 27, 2014 @ 6:06 am
Slow and steady pranayam (inhalation & exhalation) is very useful kidney problems. Specially anulom - vilom pranayam
manzoor
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Oct 7, 2014 @ 10:10 am
My urea level is 17.2. & creatine is 1.1 BUN 8.5 . Are my kidneys normal?

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