Creatinine (C4H7N3O) is the waste product formed due to the breakdown of creatine. Creatine is formed during muscle metabolism. Then, it is filtered out by our kidneys. Thus creatinine is one of the parameters for renal function tests. It is useful to know the condition of the kidney. JAFFE method is one of the most common methods for measuring the concentration of creatinine in the sample.
Everything that I state below will be on the basis of a semi-auto biochemistry analyzer and can differ from one manufacturer to another.
Normal range (approximate value) of creatinine
- Male:- 0.6 mg/dl to 1.2 mg/dl
- Female:- 0.5 mg/dl to 1.1 mg/dl
2. Urine (24 hours)
- Male:- 1.1 g to 3.0 g
- Female:- 1.1 g to 1.8 g
Handling of creatinine reagents
- Wear an apron and surgical gloves before carrying out the measurement.
- Look for the expiry date of the reagents during purchase and measurement time. Suppliers tend to give you reagent kits with a low expiry interval.
- Once you open the reagent bottles, the lifespan will decrease. So, look in your reagent kit literature for that.
- Bring the reagents and samples to room temperature before you can carry out any measurement.
- Always store reagents in the refrigerator when not in use.
Working principle (JAFFE method)
1. Principle reaction
Creatinine reacts with picric acid in an alkaline medium to form creatinine – picric acid complex which is yellow-orange in color. The color intensity is directly proportional to its concentration. More is the amount of creatinine in the serum or urine denser will be the color of the formed complex. This shows a higher absorbance value in the semi-auto biochemistry analyzer. Higher absorbance indicates a high concentration of creatinine.
2. Sample preparation
The explanation given below is in regards to the reagents of analyticon, tulip, accurex, spinreact, and diasys company. So, if you are using any other reagent besides these, then there may be some fluctuation in the programming.
Some companies provide reagents that are ready to use. In that case, you really do not need to make any working solution. However, for other reagents, you may need to make a working solution. In such a case, the composition of the working solution will be given to you in the literature of the reagent kit or in the reagent bottles.
For an end-point method like the tulip, make a reagent blank by replacing the sample/calibrator with the same volume of distilled water as shown in the table below.
When you make the solution, make sure that the total volume of the solution that you feed into the machine is more than the set sipping volume (e.g. 500 microliters).
If the concentration of creatinine is high in the sample (e.g. urine), then dilute it with 0.9% NaCl or distilled water in a ratio of 1: y. Then, when you get the final result, multiply the value with a factor (1+y).