Creatinine clearance is an examination method for determining the clearance function of the kidneys. This allows a relatively accurate determination of the glomerular filtration rate (GFR) and thus the assessment of kidney function.The term clearance refers to the removal of certain substances from the blood in a certain time.Creatinine is a metabolic product that is excreted in the urine (urinary). Creatinine is formed in muscle tissue from creatine. Creatine itself is a substance in the muscles that serves to store energy. It is released again under stress and excreted renally as creatinine.
The process
Material needed
- 24h collection urine + blood serum (for determination of serum creatinine on the day of urine collection).
Preparation of the patient
- In the morning, urine collection is started, completely discarding the morning urine of the starting day
- A drinking volume of at least 1.5 l/d must be ensured
- At the end of the collection period it is necessary that the bladder is completely emptied
Disruptive factors
- Before and during the collection period should be
- No meat should be eaten
- No heavy physical activity be performed
Glomerular filtration rate (GFR)
Normal values – women
| Gender | Normal values in ml/min |
| ≈ 25 LJ | 70-110 |
| ≈ 50TH LY | 50-100 |
| ≈ 75TH LY | 35-60 |
Normal values – men
| Gender | Normal values in ml/min |
| ≈ 25 LJ | 95-140 |
| ≈ 50TH LY | 70-115 |
| ≈ 75TH LY | 50-80 |
Normal values – children
| Age | Normal values in ml/min |
| 1st-2nd week of life (LW) | 25-35 |
| 3rd LW- 2nd month of life (LM). | 25-55 |
| 3RD-12TH LM | 35-80 |
| > 12. LM | > 90 |
In each case, the standard values are based on a body surface area of 1.73 m².
Indications
- Suspected renal disease of any kind
- Suspicion of metabolic diseases such as diabetes mellitus, hyperuricemia (uric acid metabolism disorder).
- Suspicion of collagenoses (group of connective tissue diseases caused by autoimmune processes) – systemic lupus erythematosus (SLE), polymyositis (PM) or dermatomyositis (DM), Sjögren’s syndrome (Sj), scleroderma (SSc) and Sharp syndrome (“mixed connective tissue disease”, MCTD).
- Suspected hypertension (high blood pressure).
- Suspicion of shock symptomatology
- Suspicion of toxic renal injury from drugs, exogenous toxins, or other substances
- Hemolysis (increased breakdown of red blood cells).
- Myolysis (destruction and dissolution of muscle).
- Monitoring of renal function during administration of nephrotoxic drugs.
As well as for therapy monitoring of the above diseases.
Interpretation
Interpretation of decreased values
- Decreased glomerular filtration (acute or chronic renal failure).
Acute renal failure (ANV)Prerenal
- Shock of any kind
- Desiccosis – dehydration due to lack of fluids.
Renal
- Acute renal failure due to a wide variety of triggers such as medications or sepsis (blood poisoning).
- Chronic renal failure – decreasing functionality of the kidneys.
- EPH gestosis
- Hemolysis
- Myolysis
- Plasmocytoma
- Rapid progressive glomerulonephritis
- Heavy metal intoxication
- Sepsis
Postrenal
- Obstruction of the urinary tract due to stones, tumors, or the like
- Opiates
- Parasympatholytics
.
Chronic renal failure
- Diabetic nephropathy (Kimmelstiel-Wilson syndrome).
- Glomerulonephritides
- Hypertension
- Interstitial nephritides
- Collagenoses
- Plasmocytoma kidney (Ig light chain proteinuria).
- Renovascular kidney disease
- Cystic kidneys
Interpretation of elevated values
- Glomerular hyperperfusion, eg.
- Early phase of diabetes mellitus
- Pregnancy
Further notes
- The following data must be available to calculate creatinine clearance:
- Collection period (if not exactly 24 hours).
- Urine volume
- Body size
- Body weight
- Creatinine determination is one of the most common laboratory determinations, but more and more cystatin C is used as a renal function marker. This parameter detects limitations earlier!
- Cystatin C shows greater sensitivity and specificity than serum creatinine in the range between 80-40 ml/min (GFR).
- Cystatin C is further more suitable than creatinine determination for the detection and risk classification of chronic kidney disease
- Glomerular filtration rate (GFR) and aging: among carefully studied healthy kidney donors, GFR declines at a rate of 6.3 ml/min /1.73 m2 per decade. There is reason to be concerned that older people with chronic renal failure are being misdiagnosed. In addition to this expected decline in renal function, the lowest risk of mortality (death rate) is at a GFR of ≥ 75 ml/min/ 1.73 m2 for age < 55 years, but at a lower GFR of 45 to 104 ml/min/1.73 m2 for age ≥ 65 years.
