Understanding Creatinine Normal Value: Ranges and What They Mean

Age and gender determine normal creatinine levels, but your medical history can also influence them. You should undergo extensive tests to know whether your high creatinine levels are a major problem for your body, which could indicate elevated creatinine levels and reduced kidney function.

The levels of creatine and creatinine are viewed differently: creatine (the energy molecule) and creatinine (a waste product). Creatinine levels indicate how much of this waste product is present in the body and are used to assess creatinine clearance.

Serum creatinine is used to estimate kidney function; creatinine clearance requires urine testing. The parent molecule is creatine, which is significant to the energy of muscles and is found as a dietary supplement, influencing overall creatine levels.

There is also a temporary elevation which may be due to several factors, including diet, excessive exercise, medication and infection. Your doctor may suggest additional tests to ascertain the actual cause of your high levels of creatinine. 

Creatinine is a waste product produced from the breakdown of creatine in muscle. Creatine is stored in muscle tissue and used for energy, which is why creatinine is produced at a steady rate.

• Constant Production: The rate of creatinine production is relatively constant and is mainly influenced by muscle mass in an individual (men usually have the highest level compared to women because of the large muscle mass).

• Glomerular Filtration: In healthy kidneys, this process is highly efficient, with glomeruli filtering nearly all creatinine, which is then excreted in urine. It is not severely reabsorbed by the kidneys.

• Indicator of Function: The serum creatinine is an immediate and commonly used measure of kidney activity because its synthesis is constant, and the only way to eliminate it is via the kidneys.

When the kidneys are unable to filter blood effectively due to damage or disease, creatinine levels rise, indicating potential kidney impairment.

Doctors often use serum creatinine, combined with age and sex, to calculate the estimated Glomerular Filtration Rate (eGFR), which reflects kidney function.

The eGFR is regarded as the most effective general assessment of the efficiency of the kidneys to filter the waste and thus reflects overall kidney function. Reduced kidney performance is shown by a lower eGFR (and most often increased serum creatinine).

The kidneys play key roles in maintaining the body’s internal balance, also known as homeostasis.

• Waste Elimination: They also eliminate metabolic waste materials like urea (result of protein breakdown) and creatinine (result of muscle activity), eliminating them from the blood and getting rid of them in the urine.

• Fluid Balance: They control the amount of extracellular fluid within the body and maintain the right amount of water within or outside the body.

• Electrolyte Regulation: They stabilize the concentration of some important electrolytes such as sodium, potassium and calcium in the blood.

• Acid-Base Balance: They assist in maintaining the pH level of the body either by controlling the secretion or reabsorption of acids and bases.

• Production of Hormones: They make vital hormones, such as Erythropoietin, which stimulates the formation of red blood cells. Renin, which assists in the regulation of blood pressure and Calcitriol (active Vitamin D), strengthens bones and minerals.

The standard creatinine levels are the following;

As the estimated Glomerular Filtration Rate (eGFR) is computed using the creatinine level, it is important to realize that numerous factors other than actual damage to the kidney can affect the outcome. 

These aspects are divided into two main categories, one of which has an influence on its production, including physical activity,  and the other has an influence on how they affect elevated creatinine levels or clearance.

Here is a detailed breakdown of the factors affecting blood creatinine levels, which are essential for interpreting your test results:

• Dehydration:  Dehydration reduces kidney filtration, causing creatinine to temporarily accumulate (a pre-renal increase).

• Kidney Disease/ Injury: Destruction of the nephrons (e.g. due to high blood pressure, diabetes, glomerulonephritis or even infection) decreases the actual Glomerular Filtration Rate (GFR) and results in its chronic elevation.

• Slow Renal Blood Flow: Diseases such as congestive heart failure or shock slow the blood flow to the kidney, affecting their capacity.

• Urinary Tract Obstruction: Obstructions (e.g., kidney stones, enlarged prostate) inhibit the release of the urine, and pressure accumulates, initiating impaired filtration.

Some drugs prevent the tubules from secreting creatinine actively, i.e. the serum level increases and the real GFR is unchanged. This can be referred to as a false or non-renal elevation.

• Trimethoprim (part of the antibiotic Sulfamethoxazole/ Trimethoprim or Bactrim ).

• Cimetidine (Tagamet, an over-the-counter anti-heartburn medication).

• Fenofibrate (Tricor, high triglycerides).

These medications can reduce the actual GFR:

• NSAIDs (Non-Steroidal Anti-inflammatory drugs such as Ibuprofen, Naproxen)

• ACE Inhibitors / ARBs (Applied in blood pressure; can result in an acceptable, minimal initial increase in creatinine based on the alteration of renal blood flow; however, excessive increase is an indicator of a complication).

• Some Antibiotics (e.g., aminoglycosides).

• Diuretics (Water pills), quite often, dehydrate severely.

Muscle mass determines daily creatinine production, which is crucial for calculating creatinine clearance, especially in individuals with low muscle mass.

An increase in the level of creatinine in the blood is an indicator that needs great caution, as it could be an indication that there is a severe decrease in the functioning of the kidney, or it could be a temporary effect caused by non-renal factors.

The causes are generally classified as Pre-renal (that is, affecting the blood flow to the kidney), as well as factors contributing to chronic kidney disease, Renal (that is, affecting the kidney structure itself), or Post-renal (that is, affecting the flow of urine after the kidney) and also non-renal factors affecting production or measurement.

When the level of creatinine is high, this is mainly an indication that the level of Glomerular Filtration (GFR) is really low, often associated with kidney damage. That is, the kidneys are not removing waste effectively.

Such conditions decrease the blood supply to the kidneys, and poor filtration takes place. This can be reversed in time.

• Dehydration: The most frequent reversible one. The poor fluid intake or excessive fluid loss (vomiting, diarrhoea) causes the blood volume and blood pressure to drop and lowers the amount of blood going to the kidneys.

• Congestive Heart Failure (CHF): The heart becomes unable to pump blood properly and resulting in reduced blood flow and pressure to the kidneys.

• Shock or Severe Hypotension (Low Blood Pressure): any event that results in excessive blood pressure.

• Renal Artery Stenosis: This is a constriction of the arteries that feed the kidneys, limiting the blood flow.

They include direct destruction of the filtering units (glomeruli) or tubules of the kidney.

• Chronic Kidney Disease (CKD): Long-term damage to the kidneys caused by a gradual impairment, usually as a result of:

• Diabetes Mellitus: Diabetes impairs the nephrons in the long run (Diabetic Nephropathy).

• High Blood Pressure (Hypertension): It destroys small blood vessels in the kidneys.

• Glomerulonephritis: The inflammation of the glomeruli, which usually occurs in cases of autoimmune diseases (such as Lupus) or infections.

• Polycystic Kidney Disease (PKD): This is a genetic disease that leads to the formation of fluid-filled cysts in the kidneys.

• Acute Kidney Injury (AKI): Sudden, rapid deterioration of the kidney that is due to:

• Sepsis or Severe Infection: Broad-based inflammation may destroy the kidneys.

• Nephrotoxic Drugs: Drugs which directly poison the cells of the kidney.

The effect of these conditions is that the urine gets backed up, which puts pressure on the inside of the kidney and the filtration process is hampered.

• Kidney Stones: Ureteral obstruction.

• Benign Prostatic Hyperplasia (BPH): This condition is found in men of older men, which inhibits the flow of urine out of the bladder.

• Tumors/Cancer: Mass effects in the line of the urinary tract (bladder, ureters).

All these factors increase creatinine production due to muscle breakdown, which may raise blood creatinine levels even when kidney function is normal.

• High Muscle Mass: It is normal in bodybuilders, athletes, and muscular individuals to have increased baseline creatinine.

• Vigorous activity: Vigorous exercise leads to temporary destruction of muscle, which raises creatinine levels.

• Creatine Supplements: A direct intake of creatine supplements will elevate the quantity of creatinine converted.

• High Consumption of Meat: Consumption of large quantities of cooked meat in the days preceding a blood test may temporarily raise the creatinine due to the presence of ready creatinine in cooked meat.

• Rhabdomyolysis: Extensive muscle trauma or injury causing a massive breakdown of muscle cells with the release of huge amounts of creatinine (and others).

Some drugs may alter the creatinine level either through actual destruction of the kidney or through the alteration of the measurement or secretion of creatinine. Nephrotoxic drugs can contribute to kidney injury, but they are not common causes of needing a transplant.

The following drugs reduce the real GFR:

• NSAIDs (e.g., Ibuprofen, Naproxen): When taken in substantial doses or on a long-term basis, they may damage the blood flow of the kidney.

• Aminoglycosides, Vancomycin, etc.

• Chemotherapy Agents.

Drugs that spuriously elevate (inhibit secretion) are the cause of this category. These medications inhibit the active transport systems in the kidney tubules, affecting blood creatinine levels and releasing creatinine. The true GFR does not change, and the level of blood increases.

• Trimethoprim( component of the antibiotic Septra/Bactrim).

• Cimetidine ( Tagamet, an acid reflux H2-blocker).

Fenofibrate can cause a mild rise in serum creatinine, but not dangerous by itself. It raises serum creatinine but does not reduce GFR. High creatinine levels are detected via blood tests, and urine analysis is used to assess creatinine clearance.

The management of high levels of creatinine is mainly aimed at controlling the cause of the decreased functionality of the kidneys, including chronic kidney disease.  and the adoption of lifestyle measures, including a healthy diet,  to aid in the health of the kidneys, maintain a healthy weight and even delay the onset of kidney disease.

The following are the major measures to take when dealing with high creatinine levels:

• Dietary Modifications: Diet is also a great factor that makes the kidneys work less, and the generation of nitrogenous waste is minimized.

• Moderate Protein Intake: It is possible to decrease the excessive protein consumption that strains the kidneys by lowering the urea and creatinine levels produced by the body. Nonetheless, extreme protein intake is usually not recommended because it may result in malnutrition; one should find a compromise with a nutritionist.

• Sodium Restriction: Reducing the amount of sodium in the diet will help manage high blood pressure and lower fluid retention and swelling (edema). Target intake is usually less than 2,000 mg per day.

• Potassium and Phosphorus Control: Due to the decreasing kidney function, the body is unable to eliminate potassium and phosphorus. High Potassium may lead to hazardous heart arrhythmia. Potassium-rich foods such as tomatoes, potatoes, and bananas may have to be restricted. High Phosphorus can give bones a weakened effect that may cause hyperparathyroidism. Dairy, nuts and dark soda may be limited and phosphate binders (medication) prescribed.

• Hydration: Keep the right amount of fluid. Dehydration increases creatinine, but overhydration in severe CKD can cause quite dangerous fluid buildup in the lungs and heart. Fluid intake may have to be limited in severe CKD.

All medications and supplements should be carefully reviewed because most of them have a direct or indirect impact on creatinine levels.

• Nephrotoxic Agents: Nephrotoxic drugs such as ibuprofen, which can cause damage to the kidneys and thus reduce their functioning, should be avoided or taken minimally. 

• Check Supplement Use: Discontinue creatine supplements, which directly raise creatinine production.

• Drug Changes: It may be necessary to change the dosage of any medication that is primarily excreted via the kidneys since a high creatinine/low GFR implies that the medication will remain in circulation longer.

• Treat and Prevent Anaemia and Bone Problems: Medications can be used to help treat complications:

• Avoiding Smoking Smoking increases the damage to the kidneys.

• Frequent blood studies are necessary to monitor the serum creatinine and eGFR to follow up on the progress of the treatment regimen.

• Without doing very intense exercise, which leads to rhabdomyolysis or extreme muscle wasting, regular moderate exercise is good in terms of general cardiovascular health.

To conclude, it is important to note that when the level of creatinine remains high, it is an indication that one should seek medical care to ensure that their remaining renal functions are maintained and to assess kidney function through a creatinine test, ensuring that normal creatinine levels and the health problems involved are under control.

Further examination of kidney functionality is the main contributor to assessing creatinine. It emphasises the importance of such an organ as the master filter and the controller of the body to assess kidney function through urine collection and other tests.

The kidneys have fundamental homeostatic roles; they maintain fluid and electrolyte balance, blood pressure and secretion of hormones. The most accessible and commonly used biomarker of the kidney's primary filtration process efficiency is creatinine, the constant product of muscle metabolism, measured in mg/dL, which is used to evaluate the efficiency of the process known as the Glomerular Filtration Rate (GFR).

High serum creatinine is an urgent signifier that the GFR has been impaired and is an indicator of acute, possibly reversible, harmfulness (pre-renal causes or post-renal causes), or permanent, progressive illness (intrinsic damage to the kidney). 

Management of high creatinine focuses on treating the underlying cause, particularly in kidney failure and chronic conditions that affect GFR, such as hypertension, diabetes, and diabetic kidney disease. Treatment may include obstruction removal, medication review, and lifestyle changes, in line with National Kidney Foundation guidelines. Dietary management and hydration to help reduce the load on the remaining functioning nephrons.

**Medical Disclaimer - The following information is for educational purposes only. No information provided on this website, including text, graphic, and images, are intended as substitutes for professional medical advice. Please consult with your doctor about specific medical advice pertaining to your condition(s).