This article is more than 5 years old. Information may no longer be current.
False-positive TB tests may have negative implications for HIV patients
Click Here to Manage Email Alerts
Although the danger of missing a tuberculosis diagnosis remains a concern for physicians, data indicated that false-positive tuberculosis tests increased mortality rates among patients with HIV when compared with those who received correct diagnoses, according to researchers at University of California-San Francisco and Makerere University-Kampala in Uganda, Africa.
“Studies tend to emphasize the negative impact of missing the diagnosis of TB,” Robert J. Blount, MD, clinical fellow in pulmonary and critical care medicine at UCSF’s School of Medicine, said in a press release. “Our study shows that falsely diagnosing patients with TB who do not actually have TB is also associated with negative outcomes.”
Blount and colleagues used acid-fast bacilli (AFB)–smear microscopy to determine correct and incorrect diagnoses of TB. They also monitored cumulative two-month mortality in patients with HIV suspected of having the disease to examine potential relationships between these diagnoses and adverse outcomes.
“TB remains a common cause of pulmonary disease worldwide,” Blount said. “[Patients with HIV] are particularly susceptible to TB. Diagnosis can be a challenge because the standard test — sputum culture — although sensitive and specific, often takes several weeks to yield results.”
Blount presented the study findings at the American Thoracic Society 2010 International Conference in New Orleans.
The researchers conducted the study between September 2007 and July 2009 at Mulago Hospital in Kampala, Uganda. The sample population included 600 adults with HIV who presented to the hospital with a cough that had persisted for at least two weeks and who tested positive for TB via rapid testing.
Fifty-four percent of patients had culture-positive TB, according to the researchers, and smear microscopy correctly classified 72% of patients as having true positives or true negatives. However, 7% of patients had false-positive test results, and 15% had false negatives.
The researchers also noted that the cumulative incidence of death after two months was 19% among correctly classified patients; 24% among false positives; and 31% among false negatives (P=.02).
These outcomes are likely related to a delay in investigating the true cause of disease in patients incorrectly diagnosed with TB, according to Blount. Instead, therapies for TB are used, and the actual condition goes untreated.
“These results remind us as clinicians that diagnostic tests are not 100% accurate and that falsely diagnosing patients with a disease who do not actually have that disease can lead to negative outcomes,” he said. “We must continue to re-evaluate a patient’s clinical progress. If he or she is not responding as predicted to treatment for a diagnosed disease, we must entertain alternative diagnoses.”
Blount also urged future researchers to find ways to enhance rapid diagnostic tests.
“These rapid tests … are not always as sensitive or specific for determining if a person has TB,” he said. “Further research should be focused on the development of more sensitive and specific TB diagnostic tests and the clinical impact of these new tests. Ideally, these tests should be affordable enough to be used in low-income countries, where the burden of TB is high.”
For more information:
- Blount RJ. New strategies for diagnosing latent and active tuberculosis. #A93. Presented at: American Thoracic Society 2010 International Conference; May 14-19, 2010; New Orleans.