Creatinine Blood Test in lab
Kidney Function Panel
Colorimetric Technique (Jaffe’s Method)
Formal name: Creatinine
2) What is the Creatinine?
3) Why it is required?
4) When should you get tested?
5) What are the needed preparations before the test?
1) Sample type:-
2) Sample collection method:-
3) Criteria for sample rejection:-
ِColorimetric-Kinetic technique (IFCC METHOD)
By BIOSYSTEMS kits
2) Devices used:-
Kits of Creatinine from Biosystems Company with reference code 11802, 11502, or 11542.
- Reagent A (RA) (alkaline sol.): sodium hydroxide 0.4mol/l.
- Reagent B (RB) (color reagent): picric acid 25mmol/l.
- Standard: Creatinine 2mg/l (177 µmol/l).
- Store at 15-30oC
- Reagents and standards are stable until the expiry date shown on the label when stored tightly closed, protected from light and contaminations prevented during their use.
- Indications of deterioration:
- Reagents:- presence of particles, turbidity and absorbance of the blank over 0.350 at 500 nm (1 cm cuvette).
- Standard solution:– Presence of particles and turbidity.
- Reagent preparation
- Standard (S):- ready to use
- Working Reagent: Mix equal volumes of RA and RB. Mix gently (you can prepare the working solution for each test, so, you need to mix only 500µl R1 with 500µl R2 because the cuvette needs 1 ml to be filled).
- Stable for one month at 2-8ºC.
Note:- these procedures are for spectrophotometer users, not for semi-automated users
- Clean the cuvettes if you use a spectrophotometer or semi-automated analyzer without suction system or flush the aspiration system of your semi-automated analyzer if it is with a suction system by keeping the tubing in a distilled water for 2 minutes.
- prepare the working solution as instructed by the Biosystems reagent by Mixing equal volumes of the alkaline solution (RA) and the coloring reagent (RB). The cuvette is filled by 1 ml, so, the equal volumes usually are 500µl RA with 500µl RB for each tube or cuvette.
- Bring 3 clean tubes; and add the following:
working solution (ml)
- Zero the instrument with the working solution blank at 500nm (because the reagent is not colorless)
- Incubate at 37oC for 2-5 minutes to bring it to 37oC
- Then add the serum and standard as follow:-
|working solution (ml)||1.0||1.0||1.0|
|Sample (ml)||–||0.1 (100µ)||–|
|Standard (ml)||–||–||0.1 (100µ)|
- Start the stopwatch or timer immediately after adding the standard and sample then continue incubation at 37oC.
- Read the absorbance at 500nm after 30 seconds (A1), then wait up to 90 seconds (A2) and find the concentration (see the calculations).
In the case, if you use a semi-automated analyzer, you flush the suction system if it has a suction system or clean the cuvettes if it has not a suction system and then choose the programmed procedure for Creatinine test (you program it according to the reagent supplier). In this case, you can prepare the working solution reagent in a cuvette if it has not a suction system or tube if it has a suction system. Then place the cuvettes or tubes in the thermostable cell holder of the semi-automated analyzer or the water bath, then read the blank and then add the sample, start reading immediately after adding the sample, where the analyzer starts its own timer and takes the readings as scheduled then multiply the absorbance by the factor which we will be calculated at the calculation section. (if you don’t make the analyzer start reading after adding the sample immediately, you will get false low result) DON’T forget to flush again at the end of the tests if it has the suction system. IT IS EASIER THAN SPECTROPHOTOMETER
Creatinine concentration is calculated from the following equation.
ΔAsample = ΔA1 – ΔA2 and ΔAstandard = ΔA1 – ΔA2
It is better to see the how we get this equation in the calculation section in the general concept part click here to read it.
- Cstandard = 2 mg/dl or 177 µmol/l
- ِCorrection factor =
- 37 if the concentration of the standard 2mg/dl
- 33 if the concentration of the standard 177µmol/l
See calculation section in details. click here
6) Reference range:-
|Men||0.7 – 1.2 mg/dL = 62 – 106 μmol/L|
|Women||0.5 – 0.9 mg/dL = 44 – 80 μmol/L|
Females have lower creatinine level than men because they have lower muscle mass.