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Case Report: False Negative Serum Cryptococcal Latex Agglutination Test in a Patient with Disseminated Cryptococcal Disease N. Navabi, M. Montebatsi, M. Scott, S. Gluckman and Michael J. A. Reid Journal of the International Association of Providers of AIDS Care (JIAPAC) published online 20 October 2014 DOI: 10.1177/2325957414555233 The online version of this article can be found at: http://jia.sagepub.com/content/early/2014/10/15/2325957414555233
Published by: http://www.sagepublications.com
On behalf of:
International Association of Physicians in AIDS Care
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Case Report
Case Report: False Negative Serum Cryptococcal Latex Agglutination Test in a Patient with Disseminated Cryptococcal Disease
Journal of the International Association of Providers of AIDS Care 1–4 ª The Author(s) 2014 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/2325957414555233 jiapac.sagepub.com
N. Navabi1, M. Montebatsi2, M. Scott1, S. Gluckman1, and Michael J. A. Reid1,3
Abstract A case of false-negative serum latex agglutination cryptococcal antigen (CRAG) test in a 45-year-old HIV-positive male with Cryptococcus-positive culture is described. The patient was presented to a hospital in Botswana, with breathlessness and a diffuse papular rash. His CD4 count was 25 cells/mL. Despite the suspicion for disseminated cryptococcal disease, an initial serum CRAG latex test was negative. Results of subsequent Indian ink staining, culture of cerebrospinal fluid and skin scrapings, and serum lateral flow immunoassay (LFA) were all positive for Cryptococcus neoformans. There are several possible explanations for the false-negative CRAG latex test. Given the positive LFA result, we speculate that disease may have been caused by Cryptococcus gattii, which is estimated to be responsible for between 15% and 30% of all cryptococcal diseases in Botswana. Reduced sensitivity of CRAG latex assays for detecting C gattii may lead to underdiagnosis of cryptococcal infection. Keywords Cryptococcus neoformans, serotype bias, HIV, latex agglutination
Introduction/Summary Cryptococcal meningitis is extremely common in areas with high HIV prevalence. Reports suggest that it is the most common cause of meningitis in sub-Saharan Africa (SSA), with a 1year mortality of approximately 40%.1 Early diagnosis and treatment are essential to ensure a favorable outcome. The usual symptoms include headache, fever, nausea, neck stiffness, abnormal behavior, and photophobia. However, cutaneous lesions are also recognized signs of disseminated disease. We present a case where prompt diagnosis of disseminated cryptococcosis was not made because of an initial falsenegative serum cryptococcal antigen (CRAG) test result. The accuracy of immunoassays for diagnosis of cryptococcosis is important, given the increasing use of these assays in SSA to screen and diagnose cryptococcal disease in individuals with advanced HIV and subclinical infection.2,3
that hospitalization, he was treated for pneumocystis jiroveci pneumonia (PJP) and commenced on highly active antiretroviral therapy (HAART). Initial physical examination revealed a temperature of 36.7 C, blood pressure of 145/87 mm Hg, and a pulse of 115 beats/min. His respiratory rate was 45 breaths/min, and oxygen saturation was 75% in room air. On respiratory examination, crackles were heard in the lower lung zones bilaterally. The patient was alert but disoriented to time and person. Neither meningeal signs nor focal neurological deficits were detected. He had a diffuse, umbilicated, papular rash involving his face, trunk, and arms. Many of the papules were ulcerated (Figure 1). Routine laboratory results on the day of admission included a hemoglobin level of 11.1 g/dL, platelet count 428 103/mL, white blood cell count of 3800/mL (with neutrophils, 88.8%), urea 4.7 mg/dL, creatinine 0.77 mg/dL, aspartate aminotransferase 32 mU/mL, and alanine aminotransferase 22 mU/mL.
Case Report A 45-year-old HIV-infected male presented to a district hospital in southern Botswana with a 1-week history of breathlessness. He also reported dry cough, diffuse rash, and generalized weakness that had worsened over the previous 7 days. He had been diagnosed with HIV 4 months prior when admitted to the same hospital with shortness of breath. During
1 2 3
University of Pennsylvania, Pennsylvania, PA, USA Princess Marina Hospital, Gaborone, Botswana Botswana UPenn Partnership, Gaborone, Botswana
Corresponding Author: Michael J. A. Reid, PO Box AC 157 ACH, Gaborone, Botswana. Email: [email protected]
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
2
Journal of the International Association of Providers of AIDS Care
Discussion
Figure 1.
CD4 count was 25 cells/mL. A serum blood sample sent for CRAG by latex agglutination (LA; Remel kit) was negative, following pronase pretreatment and performed according to manufacturer’s instructions. Arterial blood gases and chest X-rays were not available at the hospital. On the presumption that his respiratory distress and delirium were due to either PJP or community-acquired pneumonia, he was started on empiric therapy with parenteral cefotaxime and cotrimoxazole. Supplemental oxygen, intravenous fluids, and oral prednisolone were also initiated. The rash was attributed to Molluscum contagiosum. Unfortunately, despite these therapies, his condition deteriorated over the next 6 days. On Day 7, he was transferred to the regional referral hospital. On transfer, further investigations were performed, given the suspicion for disseminated Cryptococcus, in spite of the earlier negative serum CRAG latex result. Skin scrapings of the umbilicated papules were positive with India Ink staining and CRAG by LA. A lumbar puncture was also performed, wherein the opening pressure was 38 cm, India Ink staining of the cerebrospinal fluid (CSF) and the CRAG latex assay were positive. The CSF culture revealed heavy growth of Cryptococcus; the isolate was not speciated. Based on these findings, the patient was initiated on parenteral amphotericin B and oral fluconazole, in accordance with the local guidelines. With confirmed disseminated Cryptococcus, the initial negative serum CRAG result was called into question. A repeat serum sample was sent to an external reference laboratory for repeat CRAG testing using the latex assay (Remel kit). This test was also negative, despite pronase pretreatment and serial dilutions. By contrast, when the serum sample was processed using lateral flow immunoassay (LFA; IMMY kit), the CRAG test was positive. The patient completed 21 days of intravenous amphotericin and fluconazole (800 mg/d) at the referral hospital but remained in respiratory compromise. He died 30 days after his initial admission from respiratory failure.
HIV-associated cryptococcosis is a spectrum of diseases caused by Cryptococcus neoformans and Cryptococcus Gattii, which results in 20% to 25% of AIDS-related deaths globally each year.4 In SSA, cryptococcal infection accounts for 13% to 44% of deaths among HIV-infected adults.5–7 Due to the high morbidity and mortality associated with cryptoccoccal infection, the importance of rapid and accurate laboratory tests cannot be overstated. Immunoassays targeting the glucuronoxylomannan (GXM) antigen have become a mainstay in the diagnosis.8,9 The LA assays are considered the gold standard method, in part, because of their high sensitivity in detecting Cryptococcus both in CSF and in serum.10,11 Nevertheless, this case illustrates the potential problem of false-negative results with CRAG latex assays. There are several possible explanations for why the serum CRAG latex result was negative in our case. Rarely false negatives are caused by the prozone phenomenon (also referred to as the ‘‘hook’’ effect), when there is failure of antibody–antigen precipitation due to antibody excess12; excess antibody prevents adequate antibody cross-linking and interferes with antibody–antigen precipitation.13 The prozone effect seems unlikely in this case, since the serum sample was pretreated with a pronase enzyme before the LA immunoassay was run to mitigate the effect of antibodies preventing antibody–antigen precipitation.14 Rarely, cryptococcal disease is caused by unencapsulated Cryptococcus. This can also result in a negative CRAG test. However, it is improbable that unencapsulated Cryptococcus was the reason for the aberrant result in our case, given the positive India Ink result, which is consistent with encapsulated Cryptococcus. We speculate that this patient was infected with Cryptococcus serotype C, C gattii, for which CRAG latex assays are notoriously insensitive.2,15 That the CRAG latex assay was only positive with skin and CSF samples, presumably at very high antigen titers, would be consistent with this conclusion, since available data suggest that at high enough titers, even Cryptococcus serotype C will be positive with most CRAG latex tests.15 A recent study by Percival et al2 demonstrated that LA assays show serotype bias in GXM detection. In this study, 3 commercially available CRAG latex immunoassays all had significantly diminished sensitivity for detecting serotype C compared to serotypes A, B, or D (Table 1). The assays were only positive for C gattii (serotype C) at very high antigen titers. By contrast, most LFAs have high sensitivity for all serotypes, including serotype C, even at very low C gattii titers.2,11 While initial studies of cryptococcosis in patients with AIDS found a predominance of C neoformans var. grubi (serotype A) and C neoformans var. neoformans (serotype D) isolates,16–18 several studies suggests that the frequency of C gattii in southern Africa may be around 15%.19,20 A recent report from Botswana reported that the prevalence in our setting maybe as high as 30%.21 Because neither culture serotyping nor quantitative antigen titers are routinely performed in Botswana, we were unable to confirm that serotype bias was the explanation for the initial
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
Navabi et al
3
Table 1. Sensitivities of 3 Commercially Available Latex Agglutination Assays for Detection of GXM of Different Serotypes.a Minimum Concentration of GXM (ng/mL) Producing a Positive Resultb Ac Immunoassay
Assay format
Immunomyologics Meridian CALAS Inverness Meridian Premier
LA LA LA ELISA
Bc
Cc
Dc
CN6
MU-1
184
409
34
298
24 066
127
M0024
24 18 38 35
32 20 NT 22
27 52 64 25
68 22 NT 21
432 >2000 >2000 >2000
260 470 940 >2000
460 360 >2000 >2000
62 44 50 900
63 65 NT 630
Abbreviations: LA, latex agglutination; ELISA, antigen capture sandwich enzyme-linked immunosorbent assay; CALAS, cryptococcal antigen latex agglutination system; GXM, glucuronoxylomannan; NT, not tested. a Table reproduced with permission of Kozel et al. First published in Clinical and Vaccine Immunology, August 2011, pp. 1292-1296. b Results are shown for GXM isolated from different strains of each serotype. >2000, GXM of some strains produced negative results at all concentrations up to 2000 ng/mL. c For each serotype, selected strains deemed representative of the serotype included in analysis.
false-negative CRAG latex result. Furthermore, we only used 1 CRAG latex test—the Remel assay—and cannot confirm that other latex assays would have resulted in the same test. However, given the lack of other plausible explanations, the limitation of the CRAG latex assay used, and the established prevalence of C gattii in HIV-infected adults with cryptococcal disease in Botswana,21 this is a reasonable explanation for the false-negative serum results.
2.
3.
Summary Although most available CRAG assays have excellent operating characteristics, false-negative results can delay diagnosis and therapy. Given that substantial minority of cryptococcal infections in parts of SSA are caused by C gattii, clinicians should be aware that latex assays have significantly reduced sensitivity for detecting serotype C Cryptococcus. The prevalence of different cryptoccal serotypes should impact the choice of CRAG tests used, especially given the increasing use of serum CRAG assays for screening HIV-infected adults. Given the limitations of latex assays, we advocate for scaleup in the provision of CRAG LFA testing in high HIV prevalence settings. More fundamentally, clinicians should always be cautious about relying on a laboratory test if it does not fit with a strong clinical suspicion—especially if such a decision would have potentially grave clinical consequences, as in this case.
4.
5.
6.
7.
8.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
9.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
10.
Reference 1. Jarvis JN, Bicanic T, Loyse A, et al. Determinants of mortality in a combined cohort of 501 patients with HIV-associated
11.
Cryptococcal meningitis: implications for improving outcomes. Clin Infect Dis. 2014;58(5):736–745. Percival A, Thorkildson P, Kozel TR. Monoclonal antibodies specific for immunorecessive epitopes of glucuronoxylomannan, the major capsular polysaccharide of Cryptococcus neoformans, reduce serotype bias in an immunoassay for cryptococcal antigen. Clin Vaccine Immunol. 2011;18(8):1292–1296. Meya DB, Manabe YC, Castelnuovo B, et al. Cost-effectiveness of serum cryptococcal antigen screening to prevent deaths among HIV-infected persons with a CD4þ cell count < or ¼ 100 cells/ microL who start HIV therapy in resource-limited settings. Clin Infect Dis. 2010;51(4):448–455. Park BJ, Wannemuehler KA, Marston BJ, Govender N, Pappas PG, Chiller TM. Estimation of the current global burden of cryptococcal meningitis among persons living with HIV/AIDS. AIDS. 2009;23(4):525–530. French N, Gray K, Watera C, et al. Cryptococcal infection in a cohort of HIV-1-infected Ugandan adults. AIDS. 2002;16(7): 1031–1038. Okongo M, Morgan D, Mayanja B, Ross A, Whitworth J. Causes of death in a rural, population-based human immunodeficiency virus type 1 (HIV-1) natural history cohort in Uganda. Int J Epidemiol. 1998;27(4):698–702. Corbett EL, Churchyard GJ, Charalambos S, et al. Morbidity and mortality in South African gold miners: impact of untreated disease due to human immunodeficiency virus. Clin Infect Dis. 2002;34(9):1251–1258. Bloomfield N, Gordon MA, Elmendorf DF Jr. Detection of Cryptococcus Neoformans Antigen in Body Fluids by Latex Particle Agglutination. Proc Soc Exp Biol Med. 1963;114:64–67. Goodman JS, Kaufman L, Koenig MG. Diagnosis of cryptococcal meningitis. Value of immunologic detection of cryptococcal antigen. N Engl J Med. 1971;285(8):434–436. Babady NE, Bestrom JE, Jespersen DJ, et al. Evaluation of three commercial latex agglutination kits and a commercial enzyme immunoassay for the detection of cryptococcal antigen. Med Mycol. 2009;47(3):336–338. Jarvis JN, Percival A, Bauman S, et al. Evaluation of a novel point-of-care cryptococcal antigen test on serum, plasma, and
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12. 13.
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Journal of the International Association of Providers of AIDS Care urine from patients with HIV-associated cryptococcal meningitis. Clin Infect Dis. 2011;53(10):1019–1023. Stewart TW Jr, Parnell D. Postzone v prozone. JAMA. 1982; 248(6):646–647. Currie BP, Freundlich LF, Soto MA, Casadevall A. Falsenegative cerebrospinal fluid cryptococcal latex agglutination tests for patients with culture-positive cryptococcal meningitis. J Clin Microbiol. 1993;31(9):2519–2522. Gray LD, Roberts GD. Experience with the use of pronase to eliminate interference factors in the latex agglutination test for cryptococcal antigen. J Clin Microbiol. 1988;26(11): 2450–2451. Gates-Hollingsworth MA, Kozel TR. Serotype sensitivity of a lateral flow immunoassay for cryptococcal antigen. Clin Vaccine Immunol. 2013;20(4):634–635. Sukroongreung S, Nilakul C, Ruangsomboon O, Chuakul W, Eampokalap B. Serotypes of Cryptococcus neoformans in patients with AIDS. J Infect Dis. 1986;153(3):642.
17. Shimizu RY, Howard DH, Clancy MN The variety of Cryptococcus neoformans in patients with AIDS. J Infect Dis. 1986; 154(6):1042. 18. Swinne D, Nkurikiyinfura JB, Muyembe TL. Clinical isolates of Cryptococcus neoformans from Zaire. Eur J Clin Microbiol. 1986;5(1):50–51. 19. Litvintseva AP, Thakur R, Reller LB, Mitchell TG. Prevalence of clinical isolates of Cryptococcus gattii serotype C among patients with AIDS in Sub-Saharan Africa. J Infect Dis. 2005;192(5): 888–892. 20. Karstaedt AS, Crewe-Brown HH, Dromer F. Cryptococcal meningitis caused by Cryptococcus neoformans var. gattii, serotype C, in AIDS patients in Soweto, South Africa. Med Mycol. 2002; 40(1):7–11. 21. Steele KT, Thakur R, Nthobatsang R, Steenhoff AP, Bisson GP. In-hospital mortality of HIV-infected cryptococcal meningitis patients with C. gattii and C. neoformans infection in Gaborone, Botswana. Med Mycol. 2010;48(8):1112–1115.
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
Case Report: False Negative Serum Cryptococcal Latex Agglutination Test in a Patient with Disseminated Cryptococcal Disease N. Navabi, M. Montebatsi, M. Scott, S. Gluckman and Michael J. A. Reid Journal of the International Association of Providers of AIDS Care (JIAPAC) published online 20 October 2014 DOI: 10.1177/2325957414555233 The online version of this article can be found at: http://jia.sagepub.com/content/early/2014/10/15/2325957414555233
Published by: http://www.sagepublications.com
On behalf of:
International Association of Physicians in AIDS Care
Additional services and information for Journal of the International Association of Providers of AIDS Care (JIAPAC) can be found at: Email Alerts: http://jia.sagepub.com/cgi/alerts Subscriptions: http://jia.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav
>> OnlineFirst Version of Record - Oct 20, 2014 What is This?
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
Case Report
Case Report: False Negative Serum Cryptococcal Latex Agglutination Test in a Patient with Disseminated Cryptococcal Disease
Journal of the International Association of Providers of AIDS Care 1–4 ª The Author(s) 2014 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/2325957414555233 jiapac.sagepub.com
N. Navabi1, M. Montebatsi2, M. Scott1, S. Gluckman1, and Michael J. A. Reid1,3
Abstract A case of false-negative serum latex agglutination cryptococcal antigen (CRAG) test in a 45-year-old HIV-positive male with Cryptococcus-positive culture is described. The patient was presented to a hospital in Botswana, with breathlessness and a diffuse papular rash. His CD4 count was 25 cells/mL. Despite the suspicion for disseminated cryptococcal disease, an initial serum CRAG latex test was negative. Results of subsequent Indian ink staining, culture of cerebrospinal fluid and skin scrapings, and serum lateral flow immunoassay (LFA) were all positive for Cryptococcus neoformans. There are several possible explanations for the false-negative CRAG latex test. Given the positive LFA result, we speculate that disease may have been caused by Cryptococcus gattii, which is estimated to be responsible for between 15% and 30% of all cryptococcal diseases in Botswana. Reduced sensitivity of CRAG latex assays for detecting C gattii may lead to underdiagnosis of cryptococcal infection. Keywords Cryptococcus neoformans, serotype bias, HIV, latex agglutination
Introduction/Summary Cryptococcal meningitis is extremely common in areas with high HIV prevalence. Reports suggest that it is the most common cause of meningitis in sub-Saharan Africa (SSA), with a 1year mortality of approximately 40%.1 Early diagnosis and treatment are essential to ensure a favorable outcome. The usual symptoms include headache, fever, nausea, neck stiffness, abnormal behavior, and photophobia. However, cutaneous lesions are also recognized signs of disseminated disease. We present a case where prompt diagnosis of disseminated cryptococcosis was not made because of an initial falsenegative serum cryptococcal antigen (CRAG) test result. The accuracy of immunoassays for diagnosis of cryptococcosis is important, given the increasing use of these assays in SSA to screen and diagnose cryptococcal disease in individuals with advanced HIV and subclinical infection.2,3
that hospitalization, he was treated for pneumocystis jiroveci pneumonia (PJP) and commenced on highly active antiretroviral therapy (HAART). Initial physical examination revealed a temperature of 36.7 C, blood pressure of 145/87 mm Hg, and a pulse of 115 beats/min. His respiratory rate was 45 breaths/min, and oxygen saturation was 75% in room air. On respiratory examination, crackles were heard in the lower lung zones bilaterally. The patient was alert but disoriented to time and person. Neither meningeal signs nor focal neurological deficits were detected. He had a diffuse, umbilicated, papular rash involving his face, trunk, and arms. Many of the papules were ulcerated (Figure 1). Routine laboratory results on the day of admission included a hemoglobin level of 11.1 g/dL, platelet count 428 103/mL, white blood cell count of 3800/mL (with neutrophils, 88.8%), urea 4.7 mg/dL, creatinine 0.77 mg/dL, aspartate aminotransferase 32 mU/mL, and alanine aminotransferase 22 mU/mL.
Case Report A 45-year-old HIV-infected male presented to a district hospital in southern Botswana with a 1-week history of breathlessness. He also reported dry cough, diffuse rash, and generalized weakness that had worsened over the previous 7 days. He had been diagnosed with HIV 4 months prior when admitted to the same hospital with shortness of breath. During
1 2 3
University of Pennsylvania, Pennsylvania, PA, USA Princess Marina Hospital, Gaborone, Botswana Botswana UPenn Partnership, Gaborone, Botswana
Corresponding Author: Michael J. A. Reid, PO Box AC 157 ACH, Gaborone, Botswana. Email: [email protected]
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
2
Journal of the International Association of Providers of AIDS Care
Discussion
Figure 1.
CD4 count was 25 cells/mL. A serum blood sample sent for CRAG by latex agglutination (LA; Remel kit) was negative, following pronase pretreatment and performed according to manufacturer’s instructions. Arterial blood gases and chest X-rays were not available at the hospital. On the presumption that his respiratory distress and delirium were due to either PJP or community-acquired pneumonia, he was started on empiric therapy with parenteral cefotaxime and cotrimoxazole. Supplemental oxygen, intravenous fluids, and oral prednisolone were also initiated. The rash was attributed to Molluscum contagiosum. Unfortunately, despite these therapies, his condition deteriorated over the next 6 days. On Day 7, he was transferred to the regional referral hospital. On transfer, further investigations were performed, given the suspicion for disseminated Cryptococcus, in spite of the earlier negative serum CRAG latex result. Skin scrapings of the umbilicated papules were positive with India Ink staining and CRAG by LA. A lumbar puncture was also performed, wherein the opening pressure was 38 cm, India Ink staining of the cerebrospinal fluid (CSF) and the CRAG latex assay were positive. The CSF culture revealed heavy growth of Cryptococcus; the isolate was not speciated. Based on these findings, the patient was initiated on parenteral amphotericin B and oral fluconazole, in accordance with the local guidelines. With confirmed disseminated Cryptococcus, the initial negative serum CRAG result was called into question. A repeat serum sample was sent to an external reference laboratory for repeat CRAG testing using the latex assay (Remel kit). This test was also negative, despite pronase pretreatment and serial dilutions. By contrast, when the serum sample was processed using lateral flow immunoassay (LFA; IMMY kit), the CRAG test was positive. The patient completed 21 days of intravenous amphotericin and fluconazole (800 mg/d) at the referral hospital but remained in respiratory compromise. He died 30 days after his initial admission from respiratory failure.
HIV-associated cryptococcosis is a spectrum of diseases caused by Cryptococcus neoformans and Cryptococcus Gattii, which results in 20% to 25% of AIDS-related deaths globally each year.4 In SSA, cryptococcal infection accounts for 13% to 44% of deaths among HIV-infected adults.5–7 Due to the high morbidity and mortality associated with cryptoccoccal infection, the importance of rapid and accurate laboratory tests cannot be overstated. Immunoassays targeting the glucuronoxylomannan (GXM) antigen have become a mainstay in the diagnosis.8,9 The LA assays are considered the gold standard method, in part, because of their high sensitivity in detecting Cryptococcus both in CSF and in serum.10,11 Nevertheless, this case illustrates the potential problem of false-negative results with CRAG latex assays. There are several possible explanations for why the serum CRAG latex result was negative in our case. Rarely false negatives are caused by the prozone phenomenon (also referred to as the ‘‘hook’’ effect), when there is failure of antibody–antigen precipitation due to antibody excess12; excess antibody prevents adequate antibody cross-linking and interferes with antibody–antigen precipitation.13 The prozone effect seems unlikely in this case, since the serum sample was pretreated with a pronase enzyme before the LA immunoassay was run to mitigate the effect of antibodies preventing antibody–antigen precipitation.14 Rarely, cryptococcal disease is caused by unencapsulated Cryptococcus. This can also result in a negative CRAG test. However, it is improbable that unencapsulated Cryptococcus was the reason for the aberrant result in our case, given the positive India Ink result, which is consistent with encapsulated Cryptococcus. We speculate that this patient was infected with Cryptococcus serotype C, C gattii, for which CRAG latex assays are notoriously insensitive.2,15 That the CRAG latex assay was only positive with skin and CSF samples, presumably at very high antigen titers, would be consistent with this conclusion, since available data suggest that at high enough titers, even Cryptococcus serotype C will be positive with most CRAG latex tests.15 A recent study by Percival et al2 demonstrated that LA assays show serotype bias in GXM detection. In this study, 3 commercially available CRAG latex immunoassays all had significantly diminished sensitivity for detecting serotype C compared to serotypes A, B, or D (Table 1). The assays were only positive for C gattii (serotype C) at very high antigen titers. By contrast, most LFAs have high sensitivity for all serotypes, including serotype C, even at very low C gattii titers.2,11 While initial studies of cryptococcosis in patients with AIDS found a predominance of C neoformans var. grubi (serotype A) and C neoformans var. neoformans (serotype D) isolates,16–18 several studies suggests that the frequency of C gattii in southern Africa may be around 15%.19,20 A recent report from Botswana reported that the prevalence in our setting maybe as high as 30%.21 Because neither culture serotyping nor quantitative antigen titers are routinely performed in Botswana, we were unable to confirm that serotype bias was the explanation for the initial
Downloaded from jia.sagepub.com at TEXAS SOUTHERN UNIVERSITY on November 10, 2014
Navabi et al
3
Table 1. Sensitivities of 3 Commercially Available Latex Agglutination Assays for Detection of GXM of Different Serotypes.a Minimum Concentration of GXM (ng/mL) Producing a Positive Resultb Ac Immunoassay
Assay format
Immunomyologics Meridian CALAS Inverness Meridian Premier
LA LA LA ELISA
Bc
Cc
Dc
CN6
MU-1
184
409
34
298
24 066
127
M0024
24 18 38 35
32 20 NT 22
27 52 64 25
68 22 NT 21
432 >2000 >2000 >2000
260 470 940 >2000
460 360 >2000 >2000
62 44 50 900
63 65 NT 630
Abbreviations: LA, latex agglutination; ELISA, antigen capture sandwich enzyme-linked immunosorbent assay; CALAS, cryptococcal antigen latex agglutination system; GXM, glucuronoxylomannan; NT, not tested. a Table reproduced with permission of Kozel et al. First published in Clinical and Vaccine Immunology, August 2011, pp. 1292-1296. b Results are shown for GXM isolated from different strains of each serotype. >2000, GXM of some strains produced negative results at all concentrations up to 2000 ng/mL. c For each serotype, selected strains deemed representative of the serotype included in analysis.
false-negative CRAG latex result. Furthermore, we only used 1 CRAG latex test—the Remel assay—and cannot confirm that other latex assays would have resulted in the same test. However, given the lack of other plausible explanations, the limitation of the CRAG latex assay used, and the established prevalence of C gattii in HIV-infected adults with cryptococcal disease in Botswana,21 this is a reasonable explanation for the false-negative serum results.
2.
3.
Summary Although most available CRAG assays have excellent operating characteristics, false-negative results can delay diagnosis and therapy. Given that substantial minority of cryptococcal infections in parts of SSA are caused by C gattii, clinicians should be aware that latex assays have significantly reduced sensitivity for detecting serotype C Cryptococcus. The prevalence of different cryptoccal serotypes should impact the choice of CRAG tests used, especially given the increasing use of serum CRAG assays for screening HIV-infected adults. Given the limitations of latex assays, we advocate for scaleup in the provision of CRAG LFA testing in high HIV prevalence settings. More fundamentally, clinicians should always be cautious about relying on a laboratory test if it does not fit with a strong clinical suspicion—especially if such a decision would have potentially grave clinical consequences, as in this case.
4.
5.
6.
7.
8.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
9.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
10.
Reference 1. Jarvis JN, Bicanic T, Loyse A, et al. Determinants of mortality in a combined cohort of 501 patients with HIV-associated
11.
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