Diagnostic Use
Plasma creatinine is increased in acute and chronic renal impairment, and any condition which reduces the glomerular filtration rate (e.g. circulatory failure; post-renal obstruction).
Creatinine is formed from creatine in muscle cells, and the plasma creatinine level is dependent on muscle mass. In patients with unusually low or high muscle mass, the plasma creatinine level and the eGFR may give a misleading indication of renal function.
Levels are lower in patients with a reduced muscle mass (e.g. the elderly) and this may conceal impairment of renal function.
Ingestion of meat or fish can raise the plasma creatinine level by up to 25 umol/L for up to 8 hours.
Test Method
Middlemore Hospital lab use enzymatic method for all plasma/serum creatinine requests unless specifically asked otherwise.
Principle: Enzymatic
Analyser: Roche Diagnostics Cobas c703/c503
Reagent: CREP2
Principle: Kinetic colorimetric
Analyser: Roche Diagnostics Cobas c703/c503
Reagent: CREJ2
Limitations / Interference
Enzymatic interferences (effect on results)
- IV lignocaine (increase)
- N-acetylcysteine (decrease)
- Paracetamol metabolites in overdose and its antidote N-acetylcysteine (decrease)
- Vitamin C, ascorbic acid (decrease)
- Bilirubin, jaundice (decrease) : Total Bilirubin - Icterus >28: negative interference by around 10 to 30%. Creatinine result will be released with a comment.
- Catecholaminergic inotropes/vasopressors such as noradrenaline, adrenaline, dopamine and dobutamine (decreased)
- Alkaptonuria; Homogentisic acid: (decrease)
If your patient has one of the above conditions which can potentially cause interference and you suspect the enzymatic creatinine is affected, please write on the lab request form: Alternative Creatinine (on dopamine, lignocaine or paracetamol poisoning etc)
Creatinine on that specimen will then be assayed by the Jaffe method and reported on a separate line in concerto. Otherwise by default, the enzymatic creatinine method will be employed for all requests.
Jaffe interferences (effect on results)
- Excess proteins, especially paraprotein (increase)
- Glucose, gross hyperglycaemia (increase)
- Ketones (increase)
- Vitamin C, ascorbic acid (increase)
- Bilirubin, jaundice (decrease)
- HbF (decrease)
- Some cephalosporins (increase)