Abstract：
BACKGROUND: Cryptococcosis is an increasingly common infection given the growing immunocompromised population worldwide. Cryptococcal antigen (CrAg) testing demonstrates excellent sensitivity and specificity and is the mainstay of diagnosis. However, there may be rare instances in which false-negative CrAg results can delay diagnosis and early treatment, which are critical to ensure positive outcomes.
METHODS: A 31-year-old man living with HIV/AIDS who was not taking antiretroviral therapy was hospitalized with fever, diarrhea, and headaches. CD4 count on presentation was 71 cells/uL, and HIV viral load was 3,194,949 copies/mL. Serum CrAg testing was initially negative, however CSF CrAg performed several days later was positive at 1:40 and blood and CSF cultures grew Cryptococcus neoformans. Colonoscopy revealed mucosal papules throughout the sigmoid colon, and tissue biopsy showed yeast within the lamina propria consistent with GI cryptococcosis. Given the high burden of disease, the original serum CrAg specimen was serially diluted and subsequently found to be positive at 1:2,560, confirming the postzone phenomenon.
CONCLUSIONS: Cryptococcosis has a wide array of presentations including intraluminal GI disease, as seen in this patient. While serum CrAg testing displays excellent test characteristics, it is important for clinicians to be aware of the rare instances in which false-negative results may occur in the presence of excess antigen, as in this case.
METHODS: A 31-year-old man living with HIV/AIDS who was not taking antiretroviral therapy was hospitalized with fever, diarrhea, and headaches. CD4 count on presentation was 71 cells/uL, and HIV viral load was 3,194,949 copies/mL. Serum CrAg testing was initially negative, however CSF CrAg performed several days later was positive at 1:40 and blood and CSF cultures grew Cryptococcus neoformans. Colonoscopy revealed mucosal papules throughout the sigmoid colon, and tissue biopsy showed yeast within the lamina propria consistent with GI cryptococcosis. Given the high burden of disease, the original serum CrAg specimen was serially diluted and subsequently found to be positive at 1:2,560, confirming the postzone phenomenon.
CONCLUSIONS: Cryptococcosis has a wide array of presentations including intraluminal GI disease, as seen in this patient. While serum CrAg testing displays excellent test characteristics, it is important for clinicians to be aware of the rare instances in which false-negative results may occur in the presence of excess antigen, as in this case.
摘要：
背景：考虑到全球免疫功能低下的人群，隐球菌病是一种越来越常见的感染。隐球菌抗原（CrAg）检测具有出色的敏感性和特异性，是诊断的主要手段。然而,可能有罕见的情况下，假阴性的CrAg结果可以延迟诊断和早期治疗，这对于确保积极的结果至关重要。
方法：一名31岁的HIV/AIDS患者未接受抗逆转录病毒治疗，因发烧住院，腹泻,和头痛。CD4计数为71个细胞/uL，HIV病毒载量为3,194,949拷贝/mL。血清CrAg检测最初是阴性的，然而，几天后进行的CSFCrAg在1:40时呈阳性，血液和CSF培养物生长了新生隐球菌。结肠镜检查显示整个乙状结肠粘膜丘疹，组织活检显示固有层内的酵母与GI隐球菌病一致。鉴于疾病的高负担，对原始血清CrAg标本进行系列稀释，随后在1:2,560时发现阳性，证实了后区现象。
结论：隐球菌病有多种表现，包括腔内胃肠道疾病，从这个病人身上看到的。虽然血清CrAg测试显示优异的测试特性，对于临床医生来说，重要的是要意识到在存在过量抗原的情况下可能出现假阴性结果的罕见情况，在这种情况下。
方法：一名31岁的HIV/AIDS患者未接受抗逆转录病毒治疗，因发烧住院，腹泻,和头痛。CD4计数为71个细胞/uL，HIV病毒载量为3,194,949拷贝/mL。血清CrAg检测最初是阴性的，然而，几天后进行的CSFCrAg在1:40时呈阳性，血液和CSF培养物生长了新生隐球菌。结肠镜检查显示整个乙状结肠粘膜丘疹，组织活检显示固有层内的酵母与GI隐球菌病一致。鉴于疾病的高负担，对原始血清CrAg标本进行系列稀释，随后在1:2,560时发现阳性，证实了后区现象。
结论：隐球菌病有多种表现，包括腔内胃肠道疾病，从这个病人身上看到的。虽然血清CrAg测试显示优异的测试特性，对于临床医生来说，重要的是要意识到在存在过量抗原的情况下可能出现假阴性结果的罕见情况，在这种情况下。
