Creatinine levels and your kidney function

What is creatinine?

Creatinine is a natural waste product that’s produced by your muscles — so it’s normal to have some creatinine in your blood. If your kidneys are working correctly, they'll filter creatinine out of your blood and it will be excreted in your urine. This is why your creatinine levels can help indicate your kidney health.

What causes high creatinine levels?

The main causes of high creatinine levels include:

• kidney disease or a kidney infection
• having a higher than average amount of muscle mass
• a high protein intake — like if you eat a high-meat diet
• an underactive thyroid
• some medications — like antibiotics and steroids

Mildly raised creatinine levels can happen if you measured your levels when you were dehydrated.

What causes low creatinine levels?

The main causes of low creatinine include:

• having a lower than average amount of muscle — this is common in older adults
• certain diets — like a low-meat or low-protein diet
• an overactive thyroid
• liver disease
• amputation of a limb
• pregnancy

What is estimated glomerular filtration rate? 

Because your creatinine levels are influenced by how much muscle you have, it's important to consider factors that affect your muscle mass. This is why your creatinine level is usually combined with age and sex to calculate your estimated glomerular filtration rate (eGFR).

Your eGFR indicates how well your kidneys are functioning by estimating how much waste your kidneys can filter in a minute.  And this is considered a better marker of your kidney health than creatinine alone.

In 2021, updates were made to how eGFR should be calculated. In the past, it was recommended that ethnicity be used in this calculation. This is because black ethnic groups were assumed to have higher creatinine levels — due to muscle mass, diet, and the way the kidneys eliminate creatinine. This is no longer considered appropriate or valid. And it has the potential to overestimate kidney function in black ethnic groups — meaning people might not get the treatment they need.

What is chronic kidney disease?

If your eGFR levels indicate that you have chronic kidney disease (CKD), this means your kidneys aren’t working as well as they should. 

CKD is a long-term condition, and it’s usually caused by other conditions that put a strain on your kidneys — like high blood pressure, high cholesterol, and diabetes. 

What are the symptoms of chronic kidney disease?

In the early stages of CKD, there usually aren’t any symptoms. In more advanced cases, your symptoms might include:

• tiredness and fatigue — due to excess toxins in your blood, as well as possible anaemia (when you do not have enough healthy red blood cells)
• trouble sleeping
• dry and itchy skin — this is more common in advanced cases 
• urinating more often — especially at night
• blood or foam in your urine
• persistent puffiness around your eyes
• swollen feet and ankles

How to improve your kidney function 

There are many lifestyle factors that can help support your kidney health and how well it filters out toxins, improving your creatinine levels. These include:

• maintaining healthy blood pressure — high blood pressure can lead to kidney damage
• staying well hydrated
• eating a low-salt (sodium) diet — opt for lots of fruit, vegetables, and wholemeal foods
• keeping your blood sugar levels under control — high glucose levels can cause and worsen kidney damage
• maintaining a healthy weight
• exercising regularly
• not smoking

While chronic kidney disease isn't reversible, these healthy lifestyle factors can help slow down the progression and support your kidney health.

How to test your creatinine levels

A creatinine blood test can tell you how well your kidneys are functioning. You can get your creatinine level as part of a home blood test subscription. Note that you shouldn't eat any meat 12 hours before testing your creatinine levels.

It’s not routinely done, but you can also measure your creatinine levels with a urine test. This involves collecting urine samples over the course of 24 hours.