Procedure:
-In Blood
Sample serum or plasma
The reagent usually must be prepared before use according to kits of the  chemicals.
1.put 1 ml of working reagent in two test tubes.
2.put 100 µ of serum in one tube and read after exact 30 sec. abs1 at  wave length 500 then wait for additional 2 minutes and read again  abs2.
3.put 100 µ of standard in the other tube read after exact 30 sec. abs1  then wait for additional 2 minutes and read again abs2.
Calculation:
abs of sample (abs2 - abs1) / abs of standard (abs2 - abs1) * 2 =  .......mg / dl
-In urine
the urine must be collected for 24 hrs. then take 1ml urine and put on  it 49 ml water then take from the solution 100 µ and repeat as shown  above                                                             
Calculation:
abs of sample / abs of standard * 100 = ....... mg / dl.
Normal values
in serum or plasma 0.6 - 1.4 mg / dl
in urine 1  - 1.5 mg / dl