CREATININE TEST. Information about test and diagnosis of diseases

Dr. Yousef Al Adbai. 

                    Creatinine test

1. Purpose: Quantitative estimation of creatinine in human plasma by modified Jaffe’s method (initial rate or fixed time method) Measurement of plasma creatinine is useful in the diagnosis, treatment and follow-up of renal diseases/renal failure. Increase of serum creatinine indicates a definite damage of renal tissue.

2. Principle: Creatinine reacts with picric acid in alkaline medium to form an orange-yellow colored complex of creatinine picrate. This colored complex absorbs light at 492 nm the rate of increase in absorbance is directly proportional to the creatinine concentration in the sample.

3. Performance specifications:

3.1. Linearity: Up to 24 mg/dL in plasma.

3.2. Measurement range: 0.1–24 mg/dL of creatinine in plasma.

3.3. Sensitivity: The minimum detection limit by this kit is 1.0 mg/dL.

3.4. Specificity: This method measures a number of other non-creatinine substances also other than creatinine.

4. Primary sample:

4.1. Use only plasma as specimen for the test.

4.2. Collect 4 mL of venous blood in a heparin vacutainer tube.

4.3. Do not use lysed plasma for testing as it may give very high results.

4.4. Do not use contaminated/turbid samples for testing.

4.5. Process the sample on the same day within 3 hours of collection.

5. Type of container and additive: Use heparin vacutainer tubes for collecting blood samples.

6. Instrument: Semi-autoanalyzer

7. Reagents/Consumables:

7.1. Creatinine reagent: Picric acid 8.73 mmol/L

7.2. Buffer solution: 200 mmol/L of sodium hydroxide

7.3. 25 mmol/L of phosphate

7.4. Creatinine standard (2 mg/dL) solution containing creatinine in hydrochloric acid with preservative.

8. Procedure:

8.1. Switch on the machine and press “FLUSH ” button by keeping the tubing in a container with 2% detergent for 2 minutes followed by distilled water for 2 minutes.

8.2. Press “PROC”. Different test procedures will be displayed.

8.3. Select the test to be processed by entering its number and then press “ENTER” key.

8.4. Now the assay parameters of the specific test procedure will be displayed. Note down the volume of the reagent and the sample to be used.

8.5. Feed the blank with each batch and ensure the absorbance of reagent blank to zero

8.6. Then feed the test samples and record the values.

Assay: Fixed time (Initial rate) Reagent volume:500μL/1000μL

Wavelength: 490 nm Sample volume: 25μL/50μL

Temperature: 37°C Zero setting with distilled water

No. of readings: 2 Time: 60 sec

Concentration of Std: 2 mg/dL

9. Calculating results:

Sample absorbance× Concentration of standard = Sample concentration

Standard absorbance

10. Biological reference Range:

Male: 0.7 –1.4 mg/dL

Female: 0.6 –1.2 mg/dL

11. Critical/Mert level values: More than 30 mg/dL.

12. Laboratory interpretation: Increase of creatinine in blood suggests kidney damage.

Example: Chronic glomerulonephritis.

13. Potential sources of variability:

13.1. Lysed plasma specimens may give falsely elevated values

13.2. Creatinine remains stable in plasma for up to 2 days.

13.3. Number of substances other than creatinine interfere with the assay.

               Reference :

 Manual of Medical Laboratory Techniques