To keep an eye on your kidney function, the albumin-creatinine ratio (=ACR) is determined regularly. But what exactly does this value say and why is it so important? You will learn about this and much more in this article.
Whether you have been recently been diagnosed with kidney disease, are on dialysis, or have received a new kidney, you have probably had your albumin-creatinine ratio (ABR) determined. Simply put, this value determines how much protein is in your urine. Sometimes this value is also abbreviated as ACR - but this does not change its meaning.
The ACR value plays a crucial role in the assessment and classification of your kidney function and is therefore determined by your medical team when making the diagnosis. The ACR can be used to monitor the success of your current therapy for kidney disease, so that you can adjust your therapy if necessary. Depending on the initial value of the ACR at diagnosis, it will also be checked regularly by your medical team during the course of treatment.
The name behind this important laboratory value is a tongue twister and at first glance reveals little about its exact use. In this article, you will therefore learn everything about the ACR, the relevance of this laboratory value and what it tells you about the function of your kidney.
Why are the kidneys so important?
Your kidneys perform a number of different tasks in your body. They produce hormones such as erythropoietin (=EPO), which stimulates the formation of new red blood cells. They also regulate your blood pressure and water balance. In addition, they filter pollutants from your blood, which can become a danger to your health if they are concentrated too high.
This is why the kidney is often referred to as your body's janitor or filter. It eliminates whatever waste products accumulate in your blood during the day. To perform this function, a lot of blood flows through your kidney each day. From this blood, your urine is filtered, which contains all the pollutants and breakdown products that are later excreted when you urinate.
What exactly is the ACR?
The ACR provides important information about possible damage to your kidneys. It does this by determining how much albumin relative to creatinine is in your urine. Over the course of this article, we'll explain these two values and their relationship in detail. Simply put, the ASR tells your medical team how much protein is in your urine. But what exactly is albumin?
1. Albumin
Albumin is a protein that is produced in the liver. It is a plasma protein, which means that it is found primarily in your blood. Besides your blood, albumin is also found in your sweat, tears and saliva. In your blood, albumin serves mainly as a transport protein for important substances such as calcium, magnesium, hormones or drugs.
Normally, there is only a little albumin in your urine. Over the course of a day, the level does not usually exceed 30 mg in a person with healthy kidneys. The rest of the albumin in your blood does not pass through the kidney filter into your urine.
2. Albuminuria
In case of possible damage to your kidneys, more proteins - and therefore albumin - can get into your urine. In this case we speak of a so-called albuminuria. You can imagine the kidney filter like 3 sieves lying on top of each other. If one sieve is damaged and has larger holes, then more albumin can pass through. The amount of albumin in your urine can be used as a gauge of the health and function of your kidneys.
How is the ACR measured?
When measuring the ACR and determining possible albuminuria, the second component, creatinine, comes into play. Creatinine is a breakdown product from muscle metabolism and is excreted in your urine. As the name suggests, the ACR determines the amount of albumin in the urine in relation to creatinine in the urine over the course of the day. Accordingly, the unit of ACR is usually mg/g creatinine.
The ACR thus describes how many milligrams (=mg) of albumin in relation to grams (=g) of creatinine end up in your urine over the course of the day. Incidentally, the value can be determined either over the course of a day or at a spontaneous point in time. A typical measurement over one day requires a collection urine over 24 hours. In this case, as the name suggests, you collect your urine over one day in a container provided for this purpose. You will usually receive this from your medical team. Your ACR is then determined in the laboratory using this collected urine.
The concentration of albumin in your urine is calculated in relation to creatinine in order to minimize the influence of your urine volume (=dilution) on the concentration of albumin in the urine. The excretion of creatinine is usually constant and amounts to about 1 g per day. By calculating the concentration of albumin in relation to creatinine in your urine, the influence of your urine volume on the concentration of albumin in your urine can be reduced.
What are normal ACR values?
A normal value for your ACR is less than 30 mg/g creatinine. This means that for every 1 g of creatinine in your daily urine, there is a maximum of 30 mg of albumin. Levels above 30 mg/g may indicate kidney damage. As a rule, the higher the ASR, the higher the risk that an existing kidney disease will progress more rapidly. In this case, it is often referred to as an increased risk of progression. For this reason, if the ACR is elevated, a nephrologist is often called in directly to treat the kidney disease - if this has not already been done at this point.
Values between 30 and 300 mg/g creatinine are referred to as microalbuminuria. In contrast, levels above 300 mg/g creatinine are referred to as macroalbuminuria. In the following table, we have classified the individual stages of albuminuria according to the current Kidney Disease: Improving Global Outcomes (KDIGO) guideline:
What does ACR depend on?
As mentioned above, albuminuria can result from damage to individual components of your kidney and its filters. In addition to your kidneys, however, there are a number of other factors that can affect your ACR.
For example, a temporary increase in your ACR can be caused by physical stress, infections, high blood pressure, or certain medications. Therefore, it is important to always consider ACR in conjunction with other laboratory values and your overall health in order to identify the correct reason for deviating values. In addition, other factors such as age, gender, and your body composition (especially the amount of muscle mass) can also affect your ASR. Additionally, your ACR can fluctuate throughout the day, so it is recommended that you always collect urine at the same time.
Why is the ACR so important?
The ACR is part of the absolute basic diagnostics for suspected kidney disease. If the ACR is elevated, it is usually measured again and again during the course of the disease in order to keep a close eye on changes. This is because the ACR provides information about the current state of health of your kidney. Changes and especially an increase in albuminuria can be an indication of rapid progression of existing kidney disease. Thus, ACR serves both as a parameter in the (early) detection of kidney disease and as an important laboratory value in follow-ups.
Stable values for the ACR and other important laboratory values for your kidney function (e.g. creatinine, eGFR, etc.) indicate that the current therapy for your kidney disease seems to be working well.
How can I influence my ASR?
Just like your kidney function, you can also actively influence your ACR to some extent. The same measures that keep your kidneys generally fit and healthy are suitable for this. Some of these points are:
- Conscious nutrition, according to the stage of your kidney disease.
- Taking your medications regularly and on time
- A healthy and stable weight
- Sufficient exercise and physical activity
- Healthy blood pressure and blood sugar levels
You can find a lot more information on the listed topics in other features and content of the Mizu app. If you have any questions about your lab results or kidney health, you can always contact your medical team.
