Creatinine Blood test in lab|colorimetric Jaffé’s METHOD|General Concept

Creatinine Blood Test in lab

Kidney Function Panel

Colorimetric Technique (Jaffe’s Method)

General Concept

I) Introduction

1) Names:-

Formal name: Creatinine

Also known as: Creat; Blood Creatinine; Serum Creatinine.

2) What is the Creatinine?

Read about it in creatinine test|definition and patient eduction. Click here.

3) Why it is required?

Read about it in creatinine test|definition and patient eduction. Click here

4) When should you get tested?

Read about it in creatinine test|definition and patient eduction. Click here.

5) What are the needed preparations before the test?

Read about it in creatinine test|definition and patient eduction. Click here.

II) Required sample:-

SST tubes and LT green tubes

1) Sample type:-

a) Primary sample:-

  • Type:- serum
  • Required Sample volume:- 2 ml blood (minimum 500 μl serum).
  • Container:- Serum-separating tube (SST) (Gold or Red) or any clean tube without any additives.

b) Alternative sample:-

  • Type    :-       Plasma
  • Required Sample volume:- 2 ml blood (minimum 500 μl plasma).
  • Container     :-      Lithium heparin PST (Lt. Green). (i.e. Plasma separator tubes)

c) Storage and Stability:-

  • At room temp (15-30 oC): 4 hours;
  • Refrigerated (2-8oC) : 1 week.
  • Frozen (-200C) : 2 weeks.

d) Sample transportation

  • The sample should be refrigerated during transportation.

Question

The test requires only 100µl or 0.11ml serum or plasma. So, why the required sample is 500μl  as a minimum?

Answer:

Because you may need to repeat the test more than one time if you suspect the result or find out an error in the procedure or may be the patient’s doctor require some further testing, so, you can do it by the sample you have considering the volume of the required test and the storage period of sample that compatible with the analyte should get tested.

2) Sample collection method:-

eppendorf tube

Eppendorf tube

Serum or plasma samples are collected by collecting a blood sample from the vein through phlebotomy process by a phlebotomist, medical laboratory specialist, medical assistant or nurse who is highly trained for venipuncture process.

In case of serum sample:-

  • Collect the blood sample in the SST tube (red or gold) then allow the sample to stand for 15 to 30 min maximum to allow the blood to form a clot.
  • Then, centrifuge at 2500 rpm for 10 min.
  • Then separate the serum (the straw-colored fluid in the first layer) by a micropipette into an Eppendorf tube. Thus you can store the sample if you can’t perform the test within 3 hours or to perform other serum-requiring tests requested by the physician.


In case of plasma sample:-

  • Collect the blood sample in the Lithium heparin PST (Lt. Green) tube  Mix the sample with heparin gently without shaking.
  • Then, centrifuge at 2500 rpm for 10 min.
  • Then separate the Plasma (the straw-colored fluid in the first layer) by a micropipette into an Eppendorf tube. Thus, you can store the sample if you can’t perform the test within 3 hours or to perform other serum-requiring tests requested by the physician.

3) Criteria for sample rejection:-

  • Hemolysed serum or plasma:- because it may give very high results
  • Contaminated/turbid samples
  • If the serum or plasma is icteric (i.e. high bilirubin level) or lipaemic this should be reported and the sample not rejected.

III) The Test:-

Colorimetric-kinetic technique (Jaffé’s METHOD)

The General concept

1) Principle

1) Basics of Colorimetric technique:-

Click here to Read the basics of colorimetric technique.

2) Applying principle of colorimetric technique on the measurement of creatinine activity:-

creatinine-blood-test-equation

In creatinine test, the reaction of creatinine with picric acid, in alkaline medium, forms creatinine-picrate; the orange-yellow colored complex whose concentration is directly proportional to the creatinine concentration. The concentration of the colored complex is measured by the photometer of the spectrophotometer at 500±20nm.


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