High creatinine levels in a blood test may be a reason for concern for many people reading their test results as they are related to how well the kidneys are working and may be a sign of kidney disease.
What is creatinine?
Creatinine is the byproduct of muscle metabolism. Creatine, which is stored in the muscle, is converted to creatinine in order to produce more ATP, the energy molecule that fuels muscles. As such, creatinine is constantly released in the blood stream and its daily production is dependent on muscle mass.
Creatinine is excreted entirely by the kidneys and for this reason the serum creatinine test can be used to evaluate kidney health and to measure renal function by allowing to estimate the glomerular filtration rate (eGFR).
What is the normal range for serum creatinine?
The normal range for creatinine in the blood depends upon several factors among which there are sex, age, race, diet, and lean mass. In general, the usual reference range is:
- 0.5-1.1 mg/dl for adult women (44-97 μmol/L)
- 0.7-1.2 mg/dl for adult men (60-110 μmol/L)
- 0.5-1.0 mg/dl for adolescents (44-90 μmol/L)
In children the normal range will depend on muscle development. In the elderly, decreased values are the result of physiologic loss of muscle mass known as sarcopenia.
Causes of high creatinine in blood (elevated serum creatinine)
There are many possible causes of high creatinine levels in blood. The following are possible causes of elevated serum creatinine that do not indicate kidney disease:
- Diet and in particular red meat consumption
- Creatine supplements intake
- High muscle mass
Among the disorders and diseases that may cause the creatinine levels to rise there are:
- Acute Tubular Necrosis
- Urinary Obstruction, such as kidney stones
- Reduced renal blood flow (dehydration, shock, heart failure, …)
- Diabetic nephropathy
- Rhabdomyolysis (muscle breakdown due to trauma, injury, lack of oxygen to muscle tissue, infection, …)
- Kidney disease
Some medications can also influence test results: antibiotics, ACE inhibitors, chemotherapy and other drugs may increase serum creatinine.
Elevated BUN and creatinine ratio
Blood urea nitrogen (BUN) measures the amount of urea nitrogen in blood. Urea is the end product of protein metabolism and is formed in the liver. BUN is eliminated by the kidneys and for this reason it is another blood test which may indicate kidney disease. BUN is often evaluated in conjunction with creatinine serum levels. The BUN-to-creatinine ratio, when elevated, usually indicates an acute kidney problem as BUN tends to rise first when kidney function declines, while creatinine serum values tend to rise later and indicate chronic kidney problems.
Causes of abnormal creatinine levels in urine
Creatinine in urine is usually measured with a 24-hour urine collection test and a creatinine blood test is also performed during these 24 hours.
With elevated serum levels of creatinine and healthy kidneys, you would also expect to find increased levels of creatinine in urine due to increased excretion. Exercise, diet and pregnancy are among the possible causes of increased creatinine levels in urine, in absence of kidney disease.
On the contrary, decreased levels of creatinine in urine may indicate the limited ability of the kidneys to filter this molecule as a result of kidney disease.
High creatinine and low GFR
GFR or Glomerular Filtration Rate is the amount of blood in milliliters that each minute passes through the glomeruli, the functional units that make up the kidneys and that act as filters; GFR is generally estimated with a mathematical formula that takes into account some variables such as the age, gender, race, height, weight and serum creatinine. When GFR is estimated its acronym is eGFR and the lower the eGFR is the more severe the kidney disease is.
eGFR may indicate incorrect results due to too many variables involved and sometimes not taken into account. Several authors question the use of serum creatinine to calculate eGFR and suggest the use of blood tests other than creatinine which are more accurate such as the cystatin C levels.
How to lower creatinine
If you don’t have kidney disease and want to lower your creatinine levels, here are some suggestions:
- Increase your water intake
- Don’t take protein or creatine supplements
- Exercise with less intensity
- Reduce red meat in your diet
- Avoid using medications that are not prescribed by your physician.
To prevent kidney disease in general it is important to follow a healthy lifestyle, limiting alcohol intake, avoiding smoking, exercising regularly and maintaining a healthy weight, having a healthy diet low in salt, controlling blood sugar if diagnosed with diabetes and controlling blood pressure if suffering from hypertension.
If you have kidney disease, stick to your nephrologist advice!
What other tests are useful to understand kidney health and renal function?
Blood test results like many other tests and findings need to be evaluated by a trained professional and put in the right context. They have to be evaluated as a whole including your medical history, symptoms, medications used, lifestyle, physical examination and in conjunction with other test results; especially when the values obtained are just slightly above or below the normal ranges, by themselves they can hardly indicate any specific issue or be used to diagnose diseases. Always refer to your GP or specialist for a proper evaluation.
Other than serum creatinine, urine creatinine, BUN, GFR and eGFR, other test results that are useful to indicate renal function and the health of the kidneys are:
- Blood electrolytes, such as sodium (Na+) and potassium (K+).
- Urine test and 24-hour urine collection, to check for albumin and other proteins in urine, for the pH of urine, electrolytes, glucose, acid/base balance, osmolarity, gravity, color, …
- Medical Imaging tests, such as kidney ultrasound or CT-Scan.
What are other symptoms of kidney disease?
Early-stage kidney disease often produces few or no symptoms at all, which is why creatinine is part of many routine blood tests. Among the many symptoms that may develop over time with the progression of the disease, there are:
- Dry skin
- Muscle cramps
- Swelling feet or ankles
- High blood pressure, difficult to control with medications
- Decreased urinary volume
- Nausea or vomiting
- Loss of appetite
- Shortness of breath
- Evaluation of Elevated Creatinine.
M Shimada, B Dass – BMJ Best Practice, Oct 2020
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V Gounden, H Bhatt, I Jialal – StatPearls, Jul 2020
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KD Pagana, TJ Pagana, TN Pagana – Elsevier, 2019
- Protein and creatine supplements and misdiagnosis of kidney disease.
J Willis, R Jones – British Medical Journal, Jan 2010
- Effect of a High-Protein Diet on Kidney Function in Healthy Adults: Results from the OmniHeart Trial.
SP Juraschek, LJ Appel – American Journal of Kidney Disease, Apr 2013
- Influence of Muscle Mass and Physical Activity on Serum and Urinary Creatinine and Serum Cystatin C.
AC Baxmann, MS Ahmed – Clinical Journal of the American Society of Nephrology, Mar 2008
- False Estimates of Elevated Creatinine.
M Samra, AC Abcar – The Permanente Journal, 2012
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