Western Blot (HIV Confirmatory Test)

Clinical definition of the Western Blot test
HIV (human immunodeficiency virus) is a virus that kills or damages the body's immune system which can lead to serious infections that don't often affect healthy people. HIV enters the body through unprotected sex with an infected person via semen or vaginal fluid, contact with the blood of an infected person, sharing drug needles or via pregnant women to their babies during pregnancy. Infection with HIV causes AIDS. AIDS stands for acquired immunodeficiency syndrome and is an advanced form of an HIV infection. It can be prevented by practicing safe sex or by having AIDS medicines too. The commonly used HIV tests are

  • HIV DUO (Elisa) - To screen for HIV infection
  • Western Blot- To confirm for HIV infection
  • HIV COMBO-To check for Viral load & CD4 cell count

Why is the Western Blot test done?
A positive HIV DUO (Elisa) screening test does not necessarily indicate an HIV infection. A positive ELISA test is always followed by a Western blot test. A positive Western blot confirms infection with the human immunodeficiency virus (HIV) in serum, saliva, or urine. However, certain other conditions such as Lyme disease, syphilis, and lupus may lead to a false positive result.
A negative Western blot test would indicate that the ELISA test was a false positive test. The Western Blot conducted during the window period may give false negative results. The window period is the time it takes for the body to produce HIV antibodies after infection with the virus. In most people, this period is between 2weeks and 12 weeks.

What are the common signs/symptoms when the Western Blot test is done?
HIV infection mostly goes unnoticed & without symptoms in the early stages. People who get the virus may develop a brief cold or flu-like illness 2 to 6 weeks after becoming infected.  The immune system of the individual may get severely affected beginning with mild infections or further develop into chronic symptoms such as:

  • Swollen lymph nodes
  • Weight loss 
  • Fever 
  • Cough 
  • Shortness of breath 

During the late HIV stage, more serious symptoms may start to appear such as:

  • Swelling of lymph nodes for over 3 months 
  • Chronic diarrhea 
  • Lasting headaches 
  • Persistent, unexplained fatigue 
  • Soaking night sweats 
  • High fever (greater than 100°F ) & chills for several weeks 

Who should do the Western Blot test (Target population)?
Persons who are at a high risk of developing the disease due to unsafe sex, sharing of needles or by pregnant women suspected of transferring the infection to her baby.

What should I do before the Western Blot test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Serum (Blood Sample)

Venipuncture - Collection of blood from a vein, usually from the arm.

No Fasting Required.

No other special preparations required.

* Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Western Blot test results?

Reference Range*





Not seen

Not seen


‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Western Blot test

  • Tuberculosis 
  • Hepatitis
  • Candidiasis
  • Cryptococcal meningitis
  • Pneumocystis carinii pneumonia (PCP)
  • Histoplasmosis
  • Cryptosporidiosis
  • Toxoplasmosis

Other tests related to the Western Blot test

  • HIV Screening test
  • p24 antigen test
  • CD8 cells
  • HIV viral load
  • HIV genotypic resistance testing


Synonyms : p24Ag
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HIV - Western Blot (Confirmatory Test)