Top 7 Kidney Tests To Measure Your Kidney Function

Time has flown by once again, and therefore it is well and truly time to write my next article to help those with kidney disease. Today I wanted to cover a very important topic: kidney tests.

Kidney tests are the first stage of any great treatment program. There is no point coming in with “guns a blazing” (diets and treatments) if you don’t know exactly what has caused your condition, what degree of deterioration your condition is at, and a general reference point of where you are beginning with treatment – this is particularly important, as you want to know if all the good work is paying off!

As you are probably aware kidney disease is known as a “silent killer”. Typically because of late diagnosis, coming well after the damage has already been caused – giving little time to treat. So if you are reading this right now with only a ‘suspicion’ that something is afoot with your kidney/urinary tract health, please take this friendly suggestion and “go and have your kidneys tested this week”. This is of great importance; it may just save your life, or better yet, give you a disease-free, vital life (I’m all about quality, not quantity).

One simple way to do this (and a great place to start) is getting it done as part of your yearly check-up. There is a test known as a Comprehensive Metabolic Panel which will test many aspects of your health: liver health, heart health, nutrition levels, and of course, kidney health. Most good doctors will do this as part of your ‘yearly check-up’, but don’t take that as a given, it is not. Therefore it is always a good idea to request this test or give your doctor a friendly reminder to do so.

Kidney Tests – Overview 

Now there are many specific kidney tests available to check your kidney function, and most of these are very easy to do – simply requiring a blood sample. The most important kidney tests available are as follows:

1.    Estimated Glomerular Filtration Rate (eGFR)
2.    Creatinine
3.    24hr Creatinine Clearance
4.    Urinalysis
5.    BUN
6.    Kidney Biopsy
7.    Imaging

Kidney Tests – In Detail

What I would like to do now is just go through each of these kidney tests in detail; what they test for, how the test is performed, and any other practical information you need to know about each test:

1. Estimated Glomerular Filtration Rate (eGFR)

The eGFR kidney test is a test that estimates the total blood filtered through the kidneys every minute. Healthy kidneys filter 90ml to 120ml every minute of every hour. This occurs through the glomerular capillaries of the kidneys, hence the name.

Originally the test was known as the Glomerular Filtration Rate test (or GFR test); the calculation required a substance to be injected into the bloodstream, then collection of the urine that passed for 24 hours, and finally a test to measure how much of the substance found its way in to the urine collected. Thankfully scientists discovered they could easily estimate kidney function (mainly by measuring serum creatinine levels) with great accuracy without needing to use this original testing procedure; making it a far simpler kidney test.

The results of the eGFR test certainly give some of the most useful information about your kidney health out of all kidney tests. You see, whatever figure comes back as your result (10, 20, 50, 75, or 90ml/min), you can replace the ‘ml/min’ at the end of the result – let’s use 55ml/min as an example – with a ‘%’ instead. So in this example, 55ml/min will become 55%.

What does this mean? Well, this figure can be used to show the total percentage of kidney function you have – This person has 55% of their kidney function left. The important number to know, am I right?

Note: The eGFR kidney test requires the following information to calculate the result: creatinine serum levels (from a blood sample drawn by a needle.), age, sex, and race.

Note: A score of 60ml/min (60%) or less is considered the first stage of chronic kidney disease.

2. Creatinine

A creatinine test measures the total amount of creatinine circulating in the blood. Creatinine is a by-product of muscle breakdown that occurs in normal day-to-day functioning of the body. Creatinine in actual fact is a waste product, and therefore needs to be removed by the body; the kidneys are the elimination organ that has this role.

For that reason, testing the kidneys for the waste product will enable you to see clearly whether or not the kidneys are functioning optimally, or sub-optimally, by the amount of creatinine circulating in the bloodstream. As mentioned previously creatinine is the main substance tested for in the eGFR test.

It is important to note that there is always some amount of creatinine in the bloodstream of even healthy individuals – it’s all about balance. The reference range for blood creatinine is: 0.6- 1.2 mg per decilitre in men and 0.5- 1.1 mg per decilitre in females (in other countries 45-90 μmol/L for women and 60-110 μmol/L for men).

3. 24-hour Creatinine Clearance

Once again we find ourselves talking about creatinine as it really is the most stable and accurate substance to measure kidney function out of all kidney tests. In comparison to the simple creatinine test and in some respects the eGFR test, this test is superior as it is measured over a longer period (24 hours); and also incorporates the urine as well as the blood, thereby increasing the test’s accuracy.

To perform a creatinine clearance test two samples are required: 1. a blood sample and 2. a 24-hour urine sample. The creatinine clearance rate is then calculated by comparing the two samples. To come up with a final figure the rate is adjusted according to the patient’s body size. The reference ranges for creatinine clearance are as follows:  men: 97 to 137 ml/min and women 88 to 128 ml/min.

4. Urinalysis

As far as kidney tests go urinalysis is your first line of testing; it is quick, cheap, and anyone can do it themselves at home (though usually done at your doctor’s office). This is definitely a good place to start if you have not been diagnosed yet and want to know some basic answers fast, or is useful to track your kidney health at home if you are following a treatment plan of any kind.

Urinalysis is carried out by using ‘dipsticks’ that are typically made from plastic (or cardboard) with (usually) 9 different reagent test patches. These 9 reagent test patches once urinated on (or dipped in urine), will change colour to reflect various measurements. Just like litmus paper when measuring the acidity or alkalinity of a fluid, these 9 reagent patches will change colour reflecting the makeup of your urine, and therefore the health of your kidneys.

The following 9 elements of your urine are tested (though really 5 kidney tests are performed):

1.    Leukocytes: indicates if you have a urinary tract infection

2.    Nitrite: indicates if you have an overgrowth of bacteria in the urinary tract

3.    pH: measures the pH of your urine. This is an important measurement for kidney disease sufferers, as a key symptom of under-functioning kidneys is metabolic acidosis (=over acidity in the body). Ideally, you want your urine to have a pH of 7

4.    Protein: indicates kidney problems and/or general inflammation

5.    Glucose: indicates diabetes. Diabetes is the leading cause of kidney disease in the world

6.    Ketone bodies: indicates diabetes, fasting, or rapid weight loss

7.    Urobilinogen: indicates liver disease

8.    Bilirubin: indicates liver disease

9.    Blood: indicates kidney problems, kidney damage, kidney stones, and urinary tract infection. Note: Will give a false positive for women during menstruation – remedy this by doing the test during no-menstruation days

Note: First-morning urine is the best to test with as it is more concentrated; collect the urine midstream in a container. But this may not always be practical.

Note: Urinalysis does not provide a definitive diagnosis. All abnormal results should be followed up by additional tests by your doctor.

5. BUN

BUN stands for Blood, Urea, and Nitrogen. The premise of why this test is performed is that when the kidneys are functioning effectively they will easily remove excess levels of nitrogen (in the form of urea) via the urine. Urea is formed within the liver when the liver is metabolising protein. A normal day-to-day function. However, if the kidneys are not able to cope with the demands of this process the levels of urea and nitrogen will increase in the blood.

As you may have guessed already this test is not perfect, if there is a problem with the liver (and not the kidneys) the results will be skewed. That is why this test is commonly performed together with a creatinine test. Which as we now know is a more specific indicator of kidney function.

This kidney test is performed by taking a blood sample and is used mainly to gather more information. Therefore out of all kidney tests, this test is not imperative for diagnosis.

6. Kidney Biopsy

This is a fairly self-explanatory test, as any form of ‘biopsy’ is a test that takes a very tiny tissue sample from the part of the body in question. Once taken, the pathologist can analyse the tissue under high-tech electron microscopes to assess the type of damage caused, where it has been caused, and also in some cases diagnose the specific type of kidney disease.

It is important to note that a kidney biopsy is only performed when other kidney tests have not been able to determine a proper diagnosis, or for any of the following reasons:
•    Abnormal results – from any number of kidney tests
•    Kidney tests are unable to determine the cause of the kidney disease
•    Kidney tests show blood or protein in the urine
•    Nephrotic syndrome

A kidney biopsy can be taken in one of two manners:

1. Percutaneous biopsy: A large needle is directed through the skin, directly over the kidneys, where it takes a sample guided by an ultrasound device. This is the most common type.

2. Open biopsy: This is where tissue is taken from the kidney during surgery.

Note: Either an overnight stay or a day stay at a hospital is required.

7. Imaging

Last but not least, imaging rounds out the top 7 kidney tests available to assess kidney health. Imaging plays a vital role in the analysis of your kidneys’ health; imaging allows doctors to assess if there are any structural problems or blockages that are causing kidney disease/damage. This may include discovering kidney stones, or a blockage between the liver and kidneys causing high blood pressure.

Here is a list of the imaging techniques that may be used: ultrasound, intravenous pyelogram (IVP), CT scan (computed tomography), and isotope scan. A range of x-ray methods can also be engaged; micturating cystogram, renal arteriogram (or angiogram), or an intravenous urogram.

I hope this has shed a little more light on the kidney tests that you may have had already, are about to have, or thinking about having to assess your kidney health. In any event, know that testing is the basis of any good treatment program, and that testing never killed anyone, so please, take some positive action and get your kidney health assessed today.

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