Albumin/Creatinine Ratio (ACR)
Also called -
Urine Albumin To Creatinine Ratio (UACR).
First lets gets some understanding of what we are dealing with..
What is albumin?
Albumin is a protein and the most abundant one in human blood, making up about half of the total blood serum protein. It is produced in the liver. It provides the body with the protein needed to maintain growth and repair tissues.
It has been described as a sort of 'molecular taxi' because it ferries items like steroids, fatty acids, and thyroid hormones around the body. However its main function is to regulate the osmotic pressure of the blood.
In a person with healthy kidneys the glomerulus does not allow through passage of large molecules like albumin. However when the kidney has damage the glomerulus can become a bit like a perished rubber band and start to leak. That is when albumin starts to appear in the urine.
Why is it important?
Which proteins get excreted can tell your doctor what type of kidney disease you have. An increase in the excretion of albumin immediately raises a flag that will have him looking for chronic kidney disease (CKD), possibly due to diabetes, hypertension or Glomerular disease.
What is creatinine?
Creatinine is the waste product left when creatine phosphate is broken down in the muscles during normal muscle contractions. It passes into the blood and is carried to the kidneys where it is filtered. It then passes out of the body in the urine.
Why is it important?
As it is usually produced at a steady, constant rate by the body it can be used as a comparison factor with other substances, to check if they are being excreted normally. Low levels of creatinine in the urine can indicate kidney damage.
Creatine and albumin can be checked for individually but if there appears to be a problem your doctor may want to go further. Enter the ACR test.
What does the test for ACR do?
This compares the amount of albumin that is passing into the urine from the kidneys compared to the amount of creatinine present. Basically a ratio between two measured substance.
The advantage of calculating the albumin to creatinine ratio is that the results are not affected by any change in the concentration of the urine whereas a dipstick test is.
It estimates 24-hour urine albumin excretion so you only need a single sample - goodbye to the tedious 24 hour collection and timed specimens.
1.Creatinine levels can be affected by muscle mass, either too much (as in a body builder) or too little (as in someone with a wasting muscle disease), so that has to be taken into account.
2. If you are checking for microalbuminuria, where there are only small amounts of protein in the urine and requires greater sensitivity, it is better to use an early morning urine sample as this will be less influenced by things like the amount you have drunk and the exercise you have done.
Also, early morning urine deals with the issue of orthostatic proteinuria. This occurs most often in young adults and is simple a state in which more urinary protein is excreted when they are upright but when they are lying down it returns to normal. By the way, if you find out you are one of these folk don't panic – it has no long term consequences.
3. It is best to refrain from heavy exercise for at least 24 hours before the test. Remember creatinine production is related to muscle contraction.
4. If the first test is positive for microalbuminuria a repeat test should be done in 3-6 months time.
is a term used to describes all levels of urine albumin.
Microalbuminuria (sometimes called Incipient Nephropathy.)
is the term used to describe urine albumin levels between 30 mg/day & 300 mg/day (20 to 200 µg/min).
Macroalbuminur ( sometimes called Overt Nephropathy or Proteinuria.)
is a term used to describe albumin levels of more than 300mg/day (200 µg/min).
Lets deal with one point of confusion first.
The units used to express the results of the ACR can be either milligrams per gram (mg/g), micrograms per milligram (μg/mg) or milligrams per millimole (mg/mmol), or all of the above.
In case you receive your results in one form and wish to convert - this is how you do it.
1mg/g = 1 μg/mg = 0.113 mg/mmol.
Dividing the ACR by 8.84 converts the units (from μg/mg or mg/g to mg/mmol).
Results are worked out using a formula like this one:-
Urine albumin (mg/dL) x 1000 = ACR in mg/g
Urine creatinine (mg/dL)
For example, assuming a patient had the following values:
Urine albumin 5.6 mg/dL
Urine creatinine 91.2 mg/dL
Then dividing the albumin by creatinine gives: 0.061 mg/dL
Multiply that by 1,000 to get 61 mg albumin/g creatinine
To convert from mg albumin/g creatinine to mg albumin/mmol of creatinine multiply by 0.113.
So 61 x 0.113 = 6.89 mg/mmol
What is normal and what isn't?
In general the normal ratio is around 30 mg of albumin per gram of creatinine (30mg/g) or 3.5 mg/mmol.
However the level in men and women can differ.
For men it is often around 17 mg/g or less.
For women it is around 25 mg/g.
2.5mg/mmol or less for men.
3.5mg/mmol or less for women.
When the ARC reads:-
Between 30-300 mg /g or 3.5 - 30 mg/mmol you have Microalbuminuria.
This means there is a small amount of albumin in the urine and there may be a slight problem with your kidneys. More tests may need to be done to ascertain the extent of the damage and what, if any, treatment is required.
Microalbuminuria does not always progress to the Macroalbuminuria phase of the disease.
Above 300 mg /g or 30mg/mmol you have Macroalbuminuria.
This means there is a large amount of albumin in your urine and your kidneys are badly affected. Your doctor will look at these results and that of an eGFR test It is possible you have what is called Chronic Kidney Disease (CKD).
CKD usually will not get better and is more likely to progress. However treatment helps slow it down. Many people with mild CKD never progress to the stage of complete renal failure.
Your doctor will know your individual case and make suggestions to facilitate this.
These may include:-
1. Improving your glucose control.
The greater your HbA1c level, the greater your risk of the disease progressing. Raised blood glucose can cause a rise in the level of some chemicals within the kidney. These make the glomeruli leak more, so more albumin appears in the urine.
Also the raised blood glucose level may cause some proteins in the kidney to link together. These can cause scarring in the glomeruli (the kidneys tiny blood vessels), resulting in what is called glomerulosclerosis. Scarred tissue means the kidneys are less able to do the job of filtering properly..
2. Blood pressure control
In a way this is a little like a chicken and egg situation - kidney disease has a tendency to increase blood pressure but then increased blood pressure has a tendency to make kidney disease worse.
Controlling blood pressure is extremely important as people with CKD also have an increased risk of developing cardiovascular diseases, such as heart disease and stroke.
You may require medication to control your blood pressure. Usually it is suggested to keep it below 130/80 mm Hg, and even lower in some circumstances. Your doctor will know what is best for you. ACE inhibitors and ARBs (blood pressure drugs that help control protein loss) can slow CKD and delay kidney failure, even in people who do not have high blood pressure.
3. Lower your cholesterol level.
Medications may be required for this, especially if dietary changes don't help.
4. Dietary changes,
such as reducing salt intake and a low protein diet which lightens the work load of the kidneys.
5. Stop smoking.
6. Drink less alcohol.
8. Reviewing what mediations you are taking.
Certain medications can make kidney disease worse. Some of the main culprits are non-steroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, aspirin and naproxen.
Checked and updated April 2013