A Negative (1,3)-β-D-Glucan Result Alone Is Not Sufficient to Rule Out a Diagnosis of Pneumocystis Pneumonia in Patients With Hematological Malignancies

Abstract

Background: Serum (1,3)-β-D-glucan (BG) testing is increasingly being used in the diagnostic armamentarium for invasive fungal diseases. Given its high sensitivity, some studies suggest that a negative BG result contributes to rule out a diagnosis of Pneumocystis pneumonia (PCP). However, recent reports described a suboptimal sensitivity in HIV-negative immunocompromised patients. In this study, we evaluated the performance of BG assay for PCP diagnosis in HIV-negative patients with diverse PCP risk factors. We also assessed the correlation between Pneumocystis jirovecii load in pulmonary samples and serum BG levels. Methods: We retrospectively included HIV-negative patients with microscopically proven PCP and for whom a BG result was available. We also enrolled patients colonized by Pneumocystis as control group. Colonized patients were matched with PCP patients based on their underlying condition that exposed to PCP. Pulmonary fungal loads were determined by an in-house real-time PCR, and BG levels were measured by using the Fungitell® kit (Associates of Cape Cod, Inc.). Results: Thirty-nine patients were included in each of the two groups. Thirty-four of 39 PCP patients and one of 39 colonized patient had a positive BG test, resulting in a sensitivity of 0.87 (95% CI: 0.73-0.94), a specificity of 0.97 (95% CI: 0.87-0.99), a positive predictive value of 0.97 (95% CI: 0.85-0.99), and a negative predictive value of 0.88 (95% CI: 0.75-0.95) for BG assay. Nonetheless, median BG level differed according to the underlying condition. Among the PCP group, the lowest median level of 211 pg/ml was observed in patients with hematological malignancy (HM) and differed significantly from that observed either in solid organ transplants (3,473 pg/ml) or in patients with autoimmune or inflammatory disorder (3,480 pg/ml). Indeed, the sensitivity of BG assay was estimated at 0.64 (95% CI: 0.35-0.85) in HM patients and was lower than the one observed in the whole PCP group. Furthermore, BG level and fungal burden correlated poorly among all PCP patients. Conclusion: BG is not a reliable biomarker for ruling out PCP in HIV-negative patients with HM. Interpretation of a negative BG result should take into account, but not be limited to, the underlying condition predisposing to PCP.

Keywords: (1,3)-β-D-glucan; HIV-negative patients; Pneumocystis jirovecii; Pneumocystis pneumonia; biomarker; bronchoalveolar lavage fluid; fungal load; hematological malignancies.

Figure 1

Performance of BG assay for Pneumocystis pneumonia diagnosis in HIV-negative population. (A) Serum BG levels (pg/ml) in patients with Pneumocystis pneumonia and in colonized patients. Black horizontal bars, median values. The median value for PCP patients was 2,771 pg/ml (range, 31–5,000; interquartile range, 3,490 pg/ml). The median value for colonized patients was 31 pg/ml (range, 31–119; interquartile range, 23 pg/ml). Serum BG levels were significantly lower in the colonization group than in the PCP group (Mann–Whitney test, p < 0.001). (B) Receiver operating characteristic curve for serum BG assay performance, using microscopic detection of Pneumocystis jirovecii as the reference method. Red arrows represent calculated thresholds for maximal specificity (156 pg/ml) and maximal sensitivity (38 pg/ml). AUC, area under the curve; BG, (1,3)-β-D-glucan; and PCP, Pneumocystis pneumonia.

Figure 2

Serum BG levels (pg/ml) in patients with Pneumocystis pneumonia from HM, SOT, and SAIID subgroups. Black horizontal bars, median values. The median value for HM patients was 211 pg/ml (range, 31–2,771; interquartile range, 1,489 pg/ml). The median value for SOT patients was 3,473 pg/ml (range, 1,170–5,000; interquartile range, 2,013 pg/ml). The median value for SAIID patients was 3,480 pg/ml (range, 610–5,000; interquartile range, 2,515 pg/ml). Median BG level was significantly lower in the HM subgroup than in the SOT and SAIID subgroups (Bonferroni’s test, p < 0.05). No significant difference was observed between SOT patients and SAIID patients. BG, (1,3)-β-D-glucan; HM, hematological malignancy; ns, non-significant; SAIID, systemic autoimmune and inflammatory disorder; and SOT, solid organ transplant.

Figure 3

Performance of BG assay for Pneumocystis pneumonia diagnosis in patients suffering from hematological malignancy. (A) Serum BG levels (pg/ml) in HM patients with Pneumocystis pneupneumonia and in HM patients colonized by Pneumocystis. Black horizontal bars, median values. The median value for HM patients with PCP was 211 pg/ml (range, 31–2,271; interquartile range, 1,489 pg/ml). The median value for HM patients with colonization was 31 pg/ml (range, 31–69; interquartile range, 23 pg/ml). Serum BG levels were significantly lower in the colonization group than in the PCP group (Mann–Whitney test, p = 0.0028). (B) Receiver operating characteristic curve for serum BG assay performance in HM patients, using microscopic detection of P. jirovecii as the reference method. Red arrows represent calculated thresholds for maximal specificity (73 pg/ml) and maximal sensitivity (62.5 pg/ml). AUC, area under the curve; BG, (1,3)-β-D-glucan; HM, hematological malignancy; and PCP, Pneumocystis pneumonia.

Figure 4

Ct values in patients with Pneumocystis pneumonia from HM, SOT, and SAIID subgroups. Black horizontal bars, mean values. The mean value for HM patients was 27.09 ± 3.59 (range, 19–34). The mean value for SOT patients was 20.87 ± 3.42 (range, 15–26.5). The mean value for SAIID patients was 23.17 ± 4.14 (range, 19.5–30). Mean Ct value was significantly lower in SOT patients than in HM patients (Bonferroni’s test, p < 0.05). No significant difference was observed between SOT patients and SAIID patients or between HM patients and SAIID patients. BALF, Bronchoalveolar lavage fluid; Ct, cycle threshold; HM, hematological malignancy; ns, non-significant; SAIID, systemic autoimmune and inflammatory disorder; and SOT, solid organ transplant.