A point-of-care test for C-reactive protein (POC-CRP) greatly increased the proportion of HIV-positive Ugandan adults eligible for isoniazid preventive therapy (IPT) compared with the standard World Health Organization (WHO) symptom screen. POC-CRP would also decrease the proportion of HIV patients who need referral for further TB diagnostic testing.
TB remains a leading cause of death in HIV-positive people in sub-Saharan Africa. WHO symptom screening identifies fewer than one third of HIV patients eligible for IPT, which can prevent TB. Researchers in San Francisco, Boston, and Kampala theorized that measuring CRP, an indicator of systemic inflammation, could identify more people eligible for IPT.
The investigators measured CRP with a point-of-care assay in stored serum samples from Ugandan adults starting antiretroviral therapy. They compared the incremental discriminatory benefit of POC-CRP in determining IPT eligibility versus WHO symptom screening by calculating diagnostic accuracy in reference to baseline TB status.
The 201 study participants had a median CD4 count of 137 cells/μL (interquartile range 83 to 206), and 5 (2.5%) had TB.
POC-CRP had a sensitivity for identifying TB of 80% compared with 100% for the WHO symptom screen, a nonsignificant difference (P = 0.30). Specificity with POC-CRP was significantly higher than with the WHO screen (87% versus 21%, P < 0.0001). (Sensitivity is the ability of a test to identify people who have a certain disease, while specificity is the ability to classify people who do not have the disease as negative.)
If clinicians used the WHO symptom screen, no one who already had TB would have started IPT, while 42 of 196 people without TB (21%) would have been eligible IPT. If clinicians used POC-CRP, 1 person who already had TB would have started IPT, while 129 of 196 people without TB (66%) would have been eligible for IPT. Using POC-IPT would have resulted in a significant net IPT eligibility reclassification of 46% compared with the WHO symptom screen (P = 0.03).
The researchers also determined that using POC-IPT would have significantly lowered the proportion of HIV patients without active TB who required confirmatory TB testing (21% versus 87% with WHO screening, P < 0.0001).
The investigators conclude that “POC-CRP testing increased more than 4-fold the proportion of HIV-infected adults immediately identified as IPT eligible” and that the simple blood test “could substantially improve implementation of tuberculosis screening guidelines.”
Source: Christina Yoon, J. Lucian Davis, Laurence Huang, Conrad Muzoora, Helen Byakwaga, Colin Scibetta, David R. Bangsberg, Payam Nahid, Fred C. Semitala, Peter W. Hunt, Jeffrey N. Martin, Adithya Cattamanchi. Point-of-care C-reactive protein testing to facilitate implementation of isoniazid preventive therapy for people living with HIV. JAIDS. 2014; 65: 551-556.
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