What is creatinine?
There creatinine is a molecule present in the blood (creatininemia) and urinary level (creatinuria), which is obtained from the degradation of creatinine phosphate. Creatinine is measured by a simple blood draw and is commonly used to evaluate the kidney function of our body. High creatinine values are often linked to vardio-degree renal insufficiency, as well as dehydration or the use of certain drugs.
Functions and metabolism
There creatine phosphate, or also known as phosphocreatine, is a product found mainly in the heart and skeletal muscle, where it represents an immediate, readily usable source of energy. Following its use, a metabolite is obtained, the creatinine precisely, which is introduced into the bloodstream. From the circulation, it is then filtered at the level of the renal glomerulus and subsequently eliminated in the urine.
The evaluation of creatinine is still a routine test today, although, compared to other markers, it has a lower sensitivity. It allows to evaluate the function of the renal filter (i.e. the glomerular function).
Knowing the serum creatinine, the creatinine clearance, which gives us information on the health of the kidney. In fact, it is almost totally excreted through the urine, without being reabsorbed by the renal tubules.
Creatinine and Creatinine Clearance
Creatinine is an easily assessable parameter, both due to its wide diffusion and low cost, and thanks to the fact that it can be analyzed starting from different biological samples: blood is urine.
High values of creatininemia (i.e. of creatinine in the blood) are associated with impaired renal function. This means that the kidneys are unable to filter this product and, therefore, it remains in the bloodstream.
Being a marker of glomerular damage only, it will not give us information about the functionality or damage to the tubule.
NB It should be remembered that the nephron, or the morpho-functional unit of the kidney (i.e. the smallest portion of the kidney capable of carrying out all the functions of the organ) is made up of the glomerulus and Bowmann's capsule, together with the tubular system .
The functions of which can be summarized as follows:
- glomerulus: ultrafiltration of the blood
- system of tubules: hydro-electrolytic regulation through secretion, excretion is reabsorption of water and solutes.
Normal values of creatinine
Creatinine levels are usually expressed in μmol per L (micromol per liter) or in mg per dL (milligrams per deciliter).
The values vary according to age, sex, but also to other individual variables such as: race, dietary intake (eg protein content of the diet), physical activity practiced.
Values of creatininemia
- Female: 0.6 to 1.1 mg / dL (45-90 μmol / L)
- Male: 0.7 to 1.2 mg / dL (60-110 μmol / L)
- * Children (3-18 years): 0.5 to 1.0 mg / dL
- * Children (0-3 years): 0.3 to 0.7 mg / dL
It must be borne in mind that this parameter is susceptible to variations depending on the food diet and of muscle mass, therefore, the values of an elderly woman are not comparable to those of a young athlete. Today, rather than evaluating the net creatinine value, we resort to evaluating the creatinine clearance thus obtaining the glomerular filtration rate.
*Low creatinine in children: children, physiologically, due to a lower weight and muscle mass than adults, may have lower creatinine values. the reference values for adults.
Creatinine clearance values:
- Female: 85-130 mL / minute
- Male: 95-140 mL / minute
For clearance we mean the elimination of a substance from the blood compartment in the unit of time, therefore the amount of blood that is purified from a certain substance in 1 minute.
Calculation of creatinine clearance
There are several formulas to evaluate renal clearance, which use urinary creatine and / or blood creatinine:
C = (UxV) / P
Clearance = (Urinary concentration of the substance x Volume of urine collected in 24h) / concentration of creatinine in the blood
The limit of this formula is related to the ability to collect urine in 24 hours.
To obtain an even more precise value, the formula for the body surface area can be normalized.
C = [(UxV) / P] x [1.72 / S]
- Cockcroft-Gault formula
eGFR or VFG male: [(140 - age) * weight in kg] / [72 * serum creatinine]
eGFR or VFG female: [(140 - age) * weight in kg] / [72 * serum creatinine]
- MDRD formula (Modification of Diet in Renal Disease): as reported in this online calculator.
- CKD-EPI formula (Chronic Kidney Disease - Epidemiology Collaboration): this is currently the most used and most accurate formula (see online calculator).
The glomerular filtration rate can therefore be included among the diagnostic parameters, but it also has a prognostic role and evaluation of renal function in the follow up (therefore in the monitoring of a disease, even after treatment). In fact, it falls within the staging criteria of CKI (chronic renal failure).
The finding of high creatinine in the blood is quite frequent, and can be secondary to solvable causes such as a simple state of dehydration, or the presence of renal insufficiency, or a state of reduced functionality of the kidneys and the excretory system. This condition can be acute or chronic, and is often associated with conditions such as diabetes mellitus or high blood pressure. Let's look at the causes and symptoms of high creatinine together.
Causes of high creatinine
Among the most frequent causes of high creatinine in the blood we remember:
- Acute or chronic renal failure
- Diabetes mellitus
- Sport practiced excessively
- Kidney stones
- Prostatic pathologies
- Muscle hypertrophy
- Myasthenia gravis
- Endocrinological diseases (acromegaly, hyperthyroidism)
- Diet excessively rich in proteins and meat
- Nephrotoxic drugs (e.g. antibiotics, chemotherapy, diuretics)
There may be a form of relative high creatinine, that is linked to a condition of dehydration for which, in the absence of liquids, there is also a reduced production of urine; however, the production of creatinine remains unchanged, therefore, compared to the solvent (ie water), the concentration of creatinine is increased.
High creatininuria causes (high creatinine in the urine)
- Excessive muscular effort
High creatinine symptoms
There symptomatology found for the increase of creatinine in the blood is:
- Asthenia or tiredness
- Lack of appetite
- Swelling in the lower limbs (especially in the feet and ankles)
- Dehydrated skin
- Muscle aches and cramps
- Wheezing or dyspnea
- Painful urination and / or polyuria (frequent urination)
High creatinine: when to worry?
By studying the chronobiology of creatinine in situations of renal insufficiency it has been seen that this molecule changes in the course of Acute Renal Failure (IRA) and that, especially in the form of pre-renal IRA, therefore IRA associated with causes such as hypovolemia (reduction in blood volume following shock, burns, hemorrhages, cardiovascular insufficiency, sepsis, vasodilator drugs etc) undergoes much greater fluctuations than other forms of Renal Failure.
NB: There are 3 forms of acute kidney failure (AKI - Acute Kidney Injury):
- Pre-renal renal failure
- Intrinsic renal failure (with damage to the renal parenchyma): glomerulonephritis, interstitial nephritis, drugs and nephrotoxic substances -antibiotics, chemotherapy, diuretics, etc., hypercalcemia, rhabdomyolysis, hemolysis, autoimmune systemic diseases, sarcoidosis, lymphoma, leukemia etc).
- Post-renal renal failure (linked to obstructions to the flow of urine): eg. tumors of the ureter, ab extrinsic tumors, ureteral stones, papillary necrosis, retroperitoneal fibrosis, accidental surgical obstruction, ureteral stenosis, prostatic pathologies (benign prostatic hypertrophy, prostate cancer, neurological bladder, etc.)
Diet and Nutrition High Creatinine
What to eat in case of high creatinine?
In the presence of high creatinine in the blood it is recommended to make the following changes to the diet:
- Limit the consumption of red meat and dairy products
- Reduce your consumption of salt (sodium)
- Prefer the consumption of plant foods
- Reduce foods rich in potassium (e.g. bananas)
- Avoid taking food supplements that contain creatine
What to do in case of high creatinine?
In case of high creatinine it is advisable to contact your doctor immediately.
How to lower creatinine?
To lower creatinine you can intervene in several ways:
- Treating the triggering cause (e.g. treating hypertension, compensating for diabetes, etc.)
- Making changes to your diet and lifestyle
- Undergoing dialysis treatment (hemodialysis or peritoneal dialysis)
Low blood creatinine is just as common as a blood test result. It can be linked to blood thinning states (pregnancy) or to the presence of a reduced amount of muscle mass (very thin, undernourished people).
Causes low creatinine
A condition of high presence of creatinine in the circulation is opposed by a condition of low blood creatinine, especially associated with anemia, cachexia is muscle atrophy.
Hypo-creatininemia causes or low creatinine in the blood
- Pregnancy * (especially up to the second semester)
- Muscle atrophy
- Low protein diet
* Low creatinine finding in pregnancy may be normal.
Hypo-creatininuria or low urinary creatinine
- Renal failure (unlike blood creatinine, which increases as a result of IRA precisely because the kidney is unable to eliminate it, creatinine in the urine, again for the same reason, will be present in reduced quantities)
- Muscle pathologies
Low creatinine symptoms
- Muscle weakness
- Pallor (linked to an anemia condition)
- General malaise
How is blood creatinine measured?
Blood creatinine is measured by blood sampling. It is advisable to take some precautions before undergoing this examination, in order to have the most reliable result.
The exam is carried out on an empty stomach for at least 8 hours, preferably 12, and without having exercised in the previous 12 hours.
It is advisable to pay attention to this, because otherwise it is possible to obtain altered values, which do not correspond to the individual's objective health status.
How is creatinuria measured?
Creatinuria is measured by taking 24-hour urine collection.
Often the two tests are carried out at the same time in order to have a more precise data about renal function.
How is creatinine clearance assessed?
Creatinine clearance is measured using the previously mentioned formulas.
The study of creatine is often associated with the study ofazotemia or uremia, which is used to evaluate the presence of urea in the blood. L'urea it is a product of protein catabolism.
Other tests and markers that can be used for estimating kidney function are: Cystatin C, NGAL, KIM-1, IL-18.
Factors affecting the examination
What are the para-physiological factors that can alter the outcome of the exam?
- Meat consumption in the previous 12 hours
- High-protein diet
- Intense physical activity
The biggest limit of creatinine is represented by the fact that it is an insensitive parameter, since its increase is obtained only as a result of extensive damage to the kidney. Therefore, following minor damage (but no less important from a clinical point of view), it does not give us much information, leading to an incorrect assessment of the clinical picture. Furthermore, it can undergo alterations depending on the lifestyle and diet.