A blood test may be able to show if an HIV-positive patient
has the AIDS-defining opportunistic infection, Pneumocystis jirovecii pneumonia, US investigators report in the
July 15th edition of Clinical
Pneumocystis jirovecii was formerly known as pneumocystis carinii pneumonia (PCP), and is still commonly known as PCP. It is an AIDS-defining opportunistic infection and was one of the most frequent causes of death in the era before highly active antiretroviral therapy was introduced in 1996.
PCP typically develops when a patient has a CD4 cell count below 200
cells/mm3. Broncoscopy and induced sputum are the standard tests
used to diagnose PCP, but both are uncomfortable for the patient and difficult
and expensive to perform.
is a component of the wall of many fungi, including Pneumocystiis jirovecii. There are some data suggesting that blood
levels of β-glucan are elevated in HIV-positive and HIV-negative patients with
Dr Paul Sax and colleagues at the Brigham and Women's Hospital in Boston of the newly published study
found that β-glucan levels were strongly correlated with HIV-related PCP.
Median β-glucan levels were significantly higher among patients with PCP than
individuals who did not have this infection.
levels of β-glucan were strongly associated with the diagnosis of PCP,” comment
the investigators, who are hopeful that the test could make diagnosis of the
infection easier, avoiding the need for invasive tests such as broncoscopy or
the authors of an accompanying editorial are not convinced by the study’s
findings, concluding “this serum β-glucan test will not yet allow use to lay
down the bronchoscope.”
The study involving 252 individuals who were enrolled in the ACTG A5164
trial, a study of early versus deferred antiretroviral therapy in conjunction
with treatment for opportunistic infections.
samples of β-glucan were obtained at baseline, and results were considered
positive if β-glucan levels were above 80 pg/ml.
patients were recruited to the study between 2003 and 2008. They had advanced
immune suppression, and their median baseline CD4 cell count was 26 cells/mm3.
two-thirds (69%) of patients had PCP. Other common opportunistic infections
were cryptococcal meningitis (14%) and bacterial pneumonia (9%). In addition,
44% of patients had either oral or oesophageal thrush.
patients with PCP, the median β-glucan level was 408 pg/ml, and 92% had a
positive β-glucan test result.
comparison, the median β-glucan level for patients who did not have PCP was37
pg/ml, and 35% had a positive β-glucan test result.
differences were significant (p < 0.001).
β-glucan test had a sensitivity of 92% and a specificity of 65% for PCP.
sensitivity compares favourably to that reported for induced sputum examination
in some clinical centres,” comment the investigators.
positive predictive value of the test was 65% and the negative predictive value
strong association of β-glucan with HIV-related PCP could have significant
clinical implications, especially in settings where the induced sputum
examination for PCP is unavailable or has low sensitivity,” write the authors.
add, “β-glucan can be a helpful adjunctive test for PCP… since introducing β-glucan
testing at our institution, we have found that β-glucan testing has increased
the yield of PCP diagnoses, reduced the number of cases treated empirically, and
reduced the need for bronchoscopy.”
the authors of the accompanying editorial have reservations about the
significance of the study’s findings.
β-glucan is positive with certain other fungi; thus, results are nonspecific,”
meaning that patients “might be treated for PCP even though another pathogen
was the causative agent.” They also note that β-glucan colonisation is common
in HIV-positive patients with a low CD4 cell count even if they
do not have lung disease or PCP.
authors of the editorial were also concerned that the study did not include