Do you use a commercial test kit? Then the positive control should be included. For a home-grown test, you need a serum sample that you know is positive, that is, a sample from a diseased animal. Usually, they are around in some freezer, ask your colleagues.

Use either an endogenous soluble sample known to contain the protein you are detecting or a purified protein or peptide known to contain the immunogen sequence for the antibody you are using. A positive result from the positive control, even if the samples are negative, will indicate the procedure is optimized and working. It will verify that any negative results are valid.

Alternatively, check the antibody datasheet which will provide a suggested positive control.

You can as well check the customer review for antibody.

Amended on 13 August 2019

I must sadly declare that ELISA and RIA using Immunoglobulins/Igs/Antibodies/Abs are not quantitative and specific at all.

Such discrepancies between non-specific ELISA method and specific PDMD (Protein-Direct-Microsequencing-Deciphering) method have been found (my unpublished observation).

Four patients' liver biopsies (total five biopsies) have been obtained from The Gunma University, Maebashi, Gunma, Japan.

Clinical ELISA method has said that only one patient's serum (the patient named as No.6) is HCV(+). However, our new proteomics PDMD method has shown that all the four patients have HCV.

LC tissue (named as No.6; serum HCV(+) by clinical laboratory) has Genome polyprotein (HCV) at 7.9 μg/mg tissue protein. This tissue has no interfering virus.

HCC tissue (named as No.6; serum HCV(+) by clinical laboratory ) has Genome polyprotein (HCV) at 0.61 μg/mg tissue protein.

Liver of No.6 patient has median amount of HCV at （7.9＋0.61）/2 = 4.26 μg/mg tissue protein. HCC tissue has interfering virus Major surface antigen/Large envelope protein (HBV) at 0.17/2　＝　0.09, and Genome polyprotein (Hog cholera virus/Classical swine fever virus/CSFV) at 0.74/2 =0.37 μg/mg tissue protein. Median interfering virus becomes to be (0.09 + 0.37)/2 = 0.23 μg/mg tissue protein. The amount of HCV virus minus interfering virus becomes to be (4.26 ― 0.23) = + 4.03 μg/mg tissue protein. Therefore, ELISA of serum can have said that this patient has HCV. PDMD method showed that both LC and HCC tissues has HCV. Only this patient have shown the same result between ELISA and PDMD methods.

HCC tissue (with PBC) has Genome polyprotein (HCV) at 35.4 μg/mg tissue protein. This tissue has interfering virus of Genome polyprotein (Hog cholera virus/Classical swine fever virus/CSFV) at 43.6, DNA polymerase (HBV) at 2.2, Genome polyprotein (HAV) at 24.0, Non-structural polyprotein (HEV) at 7.5 μg/mg tissue protein, respectively. Total interfering virus becomes to be 77.3 μg/mg tissue protein. Therefore, difference of HCV minus interfering virus becomes to be (35.4　－　77.3)　＝　－41.9 μg/mg tissue protein. Then, clinical laboratory has said that this tissue is HCV (－). PDMD method clearly diagnosed that this tissue has HCV proteins.

LC tissue (with leprosy) has Genome polyprotein (HCV) at 21.9 μg/mg tissue protein. This tissue has interfering virus of RNA replicase polyprotein (Turnip yellow mosaic virus/TYMV) at 16.2, Genome polyprotein (Bean yellow mosaic virus/BYMV) at 1.5, and Genome polyprotein (HAV) at 14.4 μg/mg tissue protein, respectively. Total interfering virus becomes to be 32.1 μg/mg tissue protein. Therefore, difference of HCV minus interfering virus becomes to be (21.9　－　32.1　＝　－10.2 μg/mg tissue protein. Then, clinical laboratory has said that this tissue is HCV (－). PDMD method clearly indicated that this tissue has HCV.

Liver tissue (with pseudo-liver cancer) has Genome polyprotein (HCV) at 4.4 μg/mg tissue protein. This tissue has interfering virus of DNA polymerase (HBV) at 5.1 μg/mg tissue protein. Therefore, difference of HCV minus interfering virus becomes to be (4.4　－　5.1)　＝　－0.7 μg/mg tissue protein. Then, clinical laboratory has said that this tissue is HCV (－). But, PDMD method showed the presence of HCV clearly.

Therefore, Antibody/Ab (IgG) against HCV utilized in the clinical ELISA method has recognized also the proteins of HAV, HBV, HEV, YMV, BYMV, and CSFV.

Then, we have recently found that HepG2 has HCV and other vira, but does not have HBV (please see file; HepG2 Fucoidan). HepG2 has been said to be HBV ( + ), however this result of PDMD method indicates that notorious ELISA and/or RIA give frequently false or wrong results.

Therefore, we should use the PDMD method directly to detect and determine the infected virus and bacteria (please see files; HepG2 Fucoidan and JMBT Alopecia).

Further, we have recently demonstrated that HPLC-photometric method gives ca. 2,000-fold higher values than ELISA method in the Fucoidan determination (please see files; JCB Fucoidan Transport and ELISA Fucoidan).

By the way, we have already found that binding proteins are unexpectedly not specific. Avidin has been long considered to be a specific Biotin-binding protein, however we have found that Avidin showed higher affinty to Lipoic acid than Biotin; i.e., Avidin is a Lipoic acid/Biotin/Amino acids-binding protein (please see files; D-Asp Avidin and Lipoic acid Avidin). Therefore, we have firstly and safely determined Lipoic acid contents among many biological specimens and foodstuffs (please see file again; Lipoic acid Avidin).