Creatinine
S -Krea KL 2143
Creatinine is a byproduct produced in the body during muscle metabolism. It is formed from creatine and creatine phosphate as a result of muscle energy metabolism. Once generated, creatinine enters the bloodstream and is transported to the kidneys. There, the majority of creatinine is filtered through the glomeruli and excreted into the urine. The remaining 5-10% of creatinine is excreted through the tubules in the urine.
Indications
Assessment of renal function.
Sample
1.0 mL of serum (min. 0.5 mL). Take the serum sample before administering the drugs Litalgin and Phenindione. Refer to the section on interpretation of results – medicinal substances.
Storage and delivery
The sample can be refrigerated for up to a week, but for longer storage, it should be kept frozen. Delivery at room temperature, if it arrives within 24 hours.
Method
Spectrophotometric, enzymatic . Accredited method.
Turnaround time
1 – 2 weekdays
Reference ranges
| Age (yrs) | Women (µmol/L) | Men (µmol/L) |
|---|---|---|
| 0-2 | 10-56 | 10-56 |
| 3-5 | 10-48 | 10-48 |
| 6-12 | 10-76 | 10-76 |
| 13-16 | 15-90 | 20-95 |
| 17 | 40-90 | 50-95 |
| from 18 | 50-90 | 60-100 |
Interpretation of results
The concentration of creatinine in the bloodstream is influenced by the individual’s muscle mass and the intake of meat in their diet. Consuming a meal rich in meat can increase creatinine levels by up to 20%, making it advisable to obtain a fasting sample for accurate measurements. In kidney failure, when the serum creatinine level is significantly elevated (over 200 µmol/L), the importance of creatinine secretion through the tubules becomes more pronounced.
The serum creatinine level rises as the glomerular filtration rate (GFR) decreases. GFR naturally declines with age, but the decrease in muscle mass that comes with aging partially offsets the increase in creatinine levels. Conditions such as kidney failure and reduced kidney blood flow (e.g., due to heart failure, dehydration, and shock) can lead to decreased GFR. Additionally, obstruction of urine flow caused by urinary stones or an enlarged prostate can also raise creatinine levels.
A serum creatinine value exceeds the reference range only when only 40-50% of normal kidney glomerular filtration remains.
Creatinine values may be lower in cases of muscle atrophies, hyperthyroidism, among vegetarians, and in individuals with low muscle mass. During pregnancy, creatinine values may decrease by 10-20% due to increased glomerular filtration.
Certain medications, such as Metamizole (Litalgin) and the anticoagulant phenindione (e.g., Phenindione), can interfere with creatinine determination, leading to lower results. Toxic levels of paracetamol (producing the metabolite N-acetyl-p-benzoquinone-imine, NAPQI) and its antidote N-acetylcysteine (NAC) can also affect creatinine measurement and result in falsely low values.
Currently, Mila does not provide a GFRe value (Pt-GFRe, Pt-Glomerular filtration rate, estimated).
Inquiries
martin.tornudd@milalab.fi
Last update 8.8.2023
