Creatinine

Creatinine is a waste product that’s filtered out of your blood by your kidneys. It’s a marker of how well your kidneys are working.

What it is

When your muscles work, they produce a substance called creatine. Creatine is then converted into another substance called creatinine, which then travels through your bloodstream. Healthy kidneys are very efficient at filtering creatinine out of your blood and excreting it in your urine. The amount of creatinine in your blood is generally stable, though it can vary slightly depending on your muscle mass and activity levels. In the UK, a typical reference range for creatinine in adults is between 53 and 97 micromoles per litre (µmol/l).

Why it matters

Because your kidneys are responsible for filtering creatinine, the level of creatinine in your blood can give doctors a good idea of how well your kidneys are functioning. If your kidneys aren't filtering as effectively as they should, creatinine can build up in your blood, leading to higher levels than normal. This is why creatinine is often referred to as a key marker for kidney health.

What can cause it to be high or low

Higher than normal creatinine levels can be associated with a number of things. The most common reason is that the kidneys are not filtering waste products efficiently, which can be a sign of kidney disease or damage. This damage can happen gradually over time, or it can be due to a sudden injury to the kidneys. Other factors that can contribute to higher creatinine levels include:

• Dehydration: When you don't have enough fluid in your body, your blood can become more concentrated, leading to a temporary rise in creatinine.
• High protein diet: Eating a lot of protein can increase the amount of creatinine your body produces.
• Strenuous exercise: Intense physical activity can temporarily increase creatinine levels.
• Certain medications: Some medicines can affect kidney function or interfere with creatinine levels.
• Conditions affecting muscle breakdown: Conditions that cause significant muscle breakdown can release more creatinine into the bloodstream.

Lower than normal creatinine levels are less common and usually not a cause for concern. They can be associated with:

• Lower muscle mass: People with less muscle mass, such as the elderly or those who are very frail, may naturally have lower creatinine levels.
• Certain medical conditions: Some conditions that affect muscle health can lead to lower creatinine.
• Pregnancy: Creatinine levels can be lower during pregnancy due to changes in the body.

It's important to remember that a single creatinine reading is just one piece of information. Your doctor will consider it alongside other tests and your overall health.

Lifestyle factors that may help

Maintaining a healthy lifestyle can support overall kidney health, which in turn can help keep your creatinine levels within a healthy range. Factors that may be beneficial to discuss with your GP include:

• Staying hydrated: Ensuring you drink enough fluids throughout the day is crucial for kidney function.
• Balanced diet: Eating a diet rich in fruits, vegetables, and whole grains, while managing protein intake, can be helpful.
• Regular physical activity: Moderate exercise is generally good for your health, but it's worth discussing with your doctor how much is appropriate for you, especially if you have any existing health conditions.
• Maintaining a healthy weight: Being overweight or obese can put extra strain on your kidneys.
• Managing existing health conditions: Keeping conditions like diabetes and high blood pressure well-controlled is vital for protecting your kidneys.

Questions to discuss with your GP

If your creatinine level is outside the typical range, or if you have concerns about your kidney health, it’s a good idea to have a conversation with your GP. Here are some questions you might consider asking:

• What does my creatinine result mean in the context of my overall health?
• Are there any other tests that would be helpful to assess my kidney function?
• What are the potential causes for my specific creatinine level?
• Are there any lifestyle changes that could support my kidney health?
• What steps should I take if my creatinine level changes in the future?
• How often should my kidney function be monitored?