• What you need to confirm is that your antibody does not cross-react with anything in your sample, i.e., that it is specific for your target protein. Western blot can tell you that, if you only have a single band.
• Even if there are several bands, you can measure the intensity of the band you are interested in. Recall, however, that WB is at best a semi-quantitative method.
• Once you have established that your antibody is specific (not only to your satisfaction, but to that of the reviewer of your publication), you could use other methods like ELISA.
• Personally, I'd not use ELISA, but dot blots. In ELISA, you bind only a few percent of the target protein in your sample to the plate. In dot blots with PVDF membranes, binding is near quantitative. So your sensitivity increases by almost 2 orders of magnitude. Reproducibility also tends to be better.

Thank you very much for your helpful amswer..so you mean wb is used mainly to confirm the prese ce of the protein? I thought an elisa kit with low cross reactivity and high sensitivity would suffice..specially i am comparing between groups thus it can detect subtle changes in concentrationa..but seems i was wrong

All assays need to be validated, and part of that is to ensure specificity. This is especially true for immunological assays. Think, for example, of the HIV-test: An ELISA is used to identify samples that react with the anti-HIV antibodies. Positive samples are then investigated by WB, to check that the mass of the immune-reacting proteins is identical to the (known) mass of proteins from the virus. No sane person would give the diagnosis "infected with HIV" based solely on ELISA results.