NOTES Correlation between Serum and Plasma Antibody Titers to

The ability to utilize serum or plasma samples interchangeably is useful for tuberculosis (TB) serology. We demonstrate a strong correlation between antibody titers to several mycobacterial antigens in serum versus plasma from HIV-infected and non-HIV-infected TB and non-TB patients (r 0.99 to 0.89; P < 0.0001). Plasma and serum can be used interchangeably in the same antibody detection assays. An estimated 9.4 million new cases of active tuberculosis (TB) occur each year globally, and many are challenging to diagnose, especially those that occur in HIV-infected individ-uals (18). Much progress has been made in the field of TB serology in the past decade (10, 13, 15; reviewed in reference 16), and recent studies have indicated that serodiagnosis in the form of detection of antibodies (Abs) to immunodominant antigens of Mycobacterium tuberculosis could be a useful ad-junct test to diagnose TB earlier (2, 3, 17). Traditionally, serum is used to test for Abs to mycobacterial antigens. Serum differs from plasma in that it does not contain fibrinogen and clottin