Levels of the Candida metabolite D-arabinitol in sera of steroid-treated and untreated patients with sarcoidosis

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

D-arabinitol--a marker for invasive candidiasis

The five-carbon sugar alcohol D-arabinitol (DA) is a metabolite of most pathogenic Candida species, in vitro as well as in vivo, and can be determined by gas chromatography or enzymatic analysis. Endogenous DA and L-arabinitol (LA) are present in human body fluids, and serum DA and LA increase in renal dysfunction. In prospective clinical studies, elevated DA/LA or DA/creatine ratios in serum or urine have been found in immunocompromised, usually neutropenic, patients with invasive candidiasis. In addition, positive DA results have been obtained several days to weeks before positive blood cultures, and the normalization of DA levels has been correlated with therapeutic response in both humans and animals. However, to date, only a few prospective studies have been conducted in which adequate analytical methods were used. Thus, further investigation of various patient groups is needed to establish the applicability of the 'arabinitol method' in the diagnostic battery for invasive Candida infections.

Diagnosis of disseminated candidiasis by measurement of urine D-arabinitol/L-arabinitol ratio

Relative amounts of D-arabinitol (fungal origin) and L-arabinitol (part of normal human metabolism) in urine were determined by gas chromatography and mass spectrometry from 61 hospitalized patients with hematological malignancies. Seventeen neutropenic patients with acute leukemia (with 53 samples) had disseminated yeast infections and received empiric antifungal therapy before confirmation of the diagnosis. Control groups consisted of 22 hematologic patients (76 samples) with either mucosal (n = 10) or urinary (n = 12) Candida colonization and 22 neutropenic patients (34 samples) with no clinical or laboratory signs of invasive yeast infection. Reference values were also obtained from 50 healthy adults (50 samples). The mean urine D-arabinitol/L-arabinitol ratio +/- standard deviation (range) was 16.91 +/- 41.79 (1.41 to 254.75) in patients with disseminated infection, 2.73 +/- 2.48 (1.11 to 19.00) in colonized hematologic patients, 2.12 +/- 0.84 (1.16 to 5.84) in neutropenic controls, and 1.95 +/- 0.34 (0.97 to 3.44) in healthy adults (P < 0.001 between patients with disseminated infection and all control groups). The sensitivity and specificity of the assay for detecting disseminated yeast infection were, respectively, 88 and 91% per patient (upper limit of normal, 4.00). Seventy-one percent of patients already expressed elevated values at the onset of empiric antifungal therapy. The diagnosis of disseminated infection was confirmed on average 21.7 days after the first elevation of the D-arabinitol/L-arabinitol ratio. The method contributes to diagnosis of disseminated yeast infection and helps in monitoring patients at risk, to support the initiation of antifungal therapy at an early stage of the disease.

Laboratory aids in the diagnosis of invasive candidiasis

The laboratory diagnosis of candidiasis continues to be problematic; however, there have been several advances in the past decade which promise to enhance our ability to identify patients at high risk for infection and/or to document invasive candidiasis in critically ill and immunocompromised patients. The introduction of commercially available biphasic blood culture medium and subsequently the lysis-centrifugation procedure has markedly improved the ability of laboratories to detect fungemia. Although serologic methods have not been very successful in diagnosing candidiasis in immunocompromised patients, several antigen detection methods are now under investigation. In addition, detection of fungal metabolites such as D-arabinitol remains promising. Finally, application of the techniques of molecular biology for typing and detection of fungal pathogens has expanded our understanding of candidal infections and may offer the most sensitive and specific means of diagnosing invasive candidiasis.

Effects of gastrointestinal candidiasis, antibiotics, dietary arabinitol, and cortisone acetate on levels of the Candida metabolite D-arabinitol in rat serum and urine

We studied the effects of gastrointestinal (GI) colonization by Candida albicans, dietary arabinitol, intragastric antibiotics, and cortisone on levels of the Candida metabolite D-arabinitol in rat serum and urine. Rats given conventional laboratory chow, intragastric gentamicin and chloramphenicol, and 6.0 x 10(8) live C. albicans B311 blastoconidia by gavage had minimal invasive GI disease and no more DL-arabinitol in the urine than controls given killed C. albicans. However, colonized and uncolonized rats given intragastric antibiotics had transiently higher urine arabinitol levels than the corresponding controls given saline. Rats given conventional laboratory chow (which contained 50 micrograms of arabinitol per g) had higher serum and urine arabinitol levels than rats given no dietary arabinitol, but the differences were less than expected. Moreover, intragastric antibiotics did not cause increased arabinitol excretion in rats given no dietary arabinitol. Rats given intragastric antibiotics and live C. albicans but no dietary arabinitol had no more arabinitol in their serum or urine than controls given antibiotics and killed C. albicans or saline and live or killed C. albicans. Lastly, cortisone acetate (10 mg/kg of body weight per day intramuscularly for 10 days) did not cause increased serum or urine arabinitol levels. We conclude that neither GI colonization by C. albicans nor cortisone should interfere with the usefulness of arabinitol as a marker for invasive candidiasis; antibiotics appear to increase arabinitol excretion by suppressing GI bacteria capable of consuming dietary arabinitol.

Laboratory diagnosis of invasive candidiasis

Severe infections due to Candida species have become more frequent during the past two decades because of the increasing numbers of immunosuppressed patients being treated in our hospitals. Distinguishing colonization from invasive disease requires knowledge of the pathogenetic mechanisms leading to invasion. To assist the clinician in therapeutic decisions, clinical microbiologists should identify to species Candida organisms isolated from immunosuppressed patients. Quantitative or semiquantitative cultures of urine, burn tissues, intravascular catheter tips, and bronchoalveolar lavage specimens may provide useful information. Immunofluorescent staining of certain specimens can enhance diagnostic yield. The lysis-centrifugation blood culture technique offers some advantages over traditional broth techniques in detecting Candida fungemia. Antibody testing is of limited diagnostic value in highly immunosuppressed patients. Developing simple and reliable tests for detecting antigens or metabolites of Candida spp. in the sera of infected patients has proven difficult. Methods for typing Candida albicans are evolving. Typing should prove useful for studying the epidemiology of candidiasis in hospitalized patients.