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Journal of Clinical Microbiology, November 2006, p. 3894-3899, Vol. 44, No. 11
0095-1137/06/$08.00+0 doi:10.1128/JCM.01045-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Infectious Diseases Section,1 the Laboratory Service, VA Connecticut Healthcare System, West Haven, Connecticut,2 the Departments of Internal Medicine,3 Laboratory Medicine, Yale University School of Medicine, New Haven, Connecticut4
Received 18 May 2006/ Returned for modification 16 August 2006/ Accepted 23 August 2006
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3.9 µM/mg/dl (mean + 3 standard deviations for 30 healthy adults). High serum DA/cr's were less frequent in patients with cancer or fungemia caused by the DA nonproducer Candida glabrata than in patients with cancer or fungemia caused by a DA producer, C. albicans, C. tropicalis, or C. parapsilosis. The serum DA/cr was first
3.9 µM/mg/dl before, on the same day as, or after the first positive blood culture was drawn for 30 (36%), 22 (27%), and 11 (13%) fungemia patients, respectively. Mortality did not differ significantly among the patients with high or normal initial or peak serum DA/cr's, but mortality was higher if any serum DA/cr value was
3.9 µM/mg/dl 3 or more days after the onset of fungemia (18/27 versus 4/24 patients, respectively; P < 0.001). We conclude that serum DA/cr's are useful both for the initial diagnosis of Candida fungemia and for prognostic purposes for unselected patients with a broad range of underlying diseases and conditions. |
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Switchenko et al. (12) developed an automated enzymatic method for quantifying DA in human serum, and Walsh et al. (16) used this method in a large prospective study of high-risk, neutropenic cancer patients and bone marrow transplant recipients. That study established that most patients with serious Candida infections had high serum DA/cr's and that changes in serum DA/cr's over time correlated with the responses to antifungal therapy. One problem with the automated enzymatic DA assay is that it requires that an enzyme be purified from the pathogenic fungus Candida tropicalis. Also, most past studies have examined the diagnostic value of DA measurements primarily with high-risk patients who were treated in one or a few specialized institutions (5, 6, 8-12, 16-18), so it is not yet known if serum DA measurements are also useful for patients with a broad range of underlying conditions.
In an earlier study, we modified the automated enzymatic DA assay by (i) substituting recombinant C. albicans DA dehydrogenase, which can be produced in large amounts in Escherichia coli, for a DA dehydrogenase that was purified from C. tropicalis and (ii) quantifying NADH production fluorimetrically, which is more sensitive than the original colorimetric method (21). In the present study, we used this modified method to assess the value of serum DA measurements as an initial diagnostic method and also to assess the prognoses for 83 patients who had a wide range of underlying conditions and in whom Candida fungemia was diagnosed and treated in teaching hospitals and community hospitals throughout the state of Connecticut. The specific objectives of this study were to determine (i) the sensitivity and the specificity of elevated serum DA levels in all patients with Candida fungemia and in relevant subgroups, (ii) when during the course of Candida fungemia the serum DA levels first became elevated, and (iii) if serial serum DA levels correlated with mortality within 30 days of the onset of fungemia.
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To be included in this study, a patient was required to have (i) at least one blood culture positive for Candida; (ii) serum specimens available from at least two different days, the first of which was from the same day that the first blood sample positive by culture was drawn, 1 day earlier, or 2 days earlier; and (iii) medical records that were available for review. Single serum specimens were collected from 100 hospitalized control patients from whom blood samples for cultures were obtained for suspected infection but whose blood cultures did not yield Candida. We reviewed each fungemic patient's medical records for information on age, gender, underlying conditions, treatment with steroids or other immunosuppressive drugs, use of antifungal drugs either for prophylaxis or for therapy, and survival for 30 days after the onset of fungemia. A Charlson comorbidity score was calculated for each patient (3). The nonfungemic control patients' medical records were reviewed for information on age, gender, underlying diseases, the results of laboratory tests other than blood cultures, and the final outcome of hospitalization. Single serum specimens were also collected from 30 healthy hospital employees.
D-Arabinitol measurements. Serum specimens were stored at 4°C at the participating hospitals until they were retrieved by study personnel. They were then transported to the study laboratory at the VA Connecticut Healthcare System, where they were stored at 80°C. The specimens were thawed, diluted 1:1 (vol/vol) with 10 mM sodium citrate (pH 4.0), boiled for 10 min, and cooled on ice; and the supernatants obtained by centrifugation at 10,000 x g for 10 min were analyzed for D-arabinitol by a rapid, automated enzymatic fluorometric assay. The key reagent in this assay is a recombinant C. albicans DA dehydrogenase that is produced in E. coli and purified by dye ligand affinity chromatography. Formal validation studies have established that this assay can quantify DA in human serum with high degrees of accuracy and precision (21). To correct for the effects of renal function on serum DA levels, creatinine was measured by the modified Jaffee alkaline picrate reaction with an Hitachi 717 chemistry instrument, and the DA/cr's were calculated and expressed as the DA concentration (µM)/creatinine concentration (mg per dl) (6, 16, 17, 21).
Microbiology methods. All Candida isolates were transferred to Sabouraud's dextrose agar and stored. Subcultures were sent to the CDC laboratories, where the species were determined and the organisms were tested for their susceptibilities to several antifungal drugs (7).
Statistical methods. The Mann-Whitney test was used for continuous variables, and the Fisher exact test was used for discontinuous variables. All P values were two tailed, and a P value <0.05 was considered significant.
Human investigation committee approvals. This study was approved by the Human Investigations Committees of the VA Connecticut Healthcare System, Yale University School of Medicine, the Connecticut Hospital Association, and all participating hospitals.
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Eighty-three patients with Candida fungemia qualified for this study, and 345 serum specimens were available from these patients (mean, 4.16 serum specimens per patient; median, 4 serum specimens per patient; range, 2 to 8 specimens per patient). The mean ± SD age of the fungemic patients was 62.7 ± 18.8 years (range, 1 to 87 years). The fungemic patients included 39 (47%) males, 3 (3.6%) with human immunodeficiency virus infection or AIDS, 15 (18%) with neutropenia, 28 (34%) with cancer, and 25 (30%) who had undergone abdominal surgery during the current hospitalization. Prior to the onset of fungemia, 80 patients (96%) had received antibacterial drugs, 34 (41%) had received corticosteroids or other immunosuppressive drugs, 22 (26%) had received antifungal prophylaxis, 70 (84%) had at least one indwelling intravenous catheter, and 60 (72%) had at least one central venous catheter.
Forty-eight fungemic patients were infected with C. albicans, 10 with Candida tropicalis, 10 with Candida glabrata, 7 with Candida parapsilosis, 3 with Candida lusitaniae, 3 with Candida krusei, and 2 with undetermined Candida species. Seventy patients (84%) received systemic antifungal therapy after fungemia was recognized. Forty fungemic patients (48%) died within 30 days of the onset of fungemia, including 33 who received systemic antifungal therapy and 7 who did not.
Serum DA/cr's for initial diagnosis of Candida fungemia.
The mean ± SD DA/cr's for 30 healthy hospital employees was 1.4 ± 0.8 µM/mg/dl, and we defined the upper limit of normal as 3 SDs above the mean for this group (3.9 µM/mg/dl). The serum DA/cr's for the nonfungemic controls with gram-negative bacteremia, gram-positive bacteremia, other infections, or no known infection were not significantly different; so the serum DA/cr's for these groups were combined. The mean serum DA/cr and the proportion of patients with serum DA/cr's
3.9 µM/mg/dl were higher for the hospitalized nonfungemic controls than for the healthy adults, but these differences were not quite significant (Table 1). The 11 nonfungemic control patients with serum DA/cr's
3.9 µM/mg/dl included 6 patients with gram-positive or gram-negative bacteremia, 2 with Candida species isolated in culture from the sputum and stool, 1 with a wound infection, and 2 with no known infection. Four of the 11 nonfungemic controls with high serum DA/cr's had multiorgan failure and rapidly deteriorating renal function.
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TABLE 1. Serum D-arabinitol/creatinine ratios
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3.9 µM/mg/dl (Table 1). Because the analysis of multiple specimens per fungemic patient and only one specimen per control was a potential source of bias, we repeated the analysis using only the initial DA/cr for each fungemic patient (defined as the DA/cr on the first day of fungemia or the day closest to that day, depending on availability of serum specimens). The initial DA/cr and the proportion of patients with high initial DA/cr's were also higher for the fungemic patients than for the nonfungemic controls (Table 1).
C. albicans, C. tropicalis, and C. parapsilosis produce DA in culture; but C. glabrata does not (2). When the fungemic patients were analyzed according to Candida species, the groups infected with C. albicans, C. tropicalis, and C. parapsilosis had higher initial and peak DA/cr's than the nonfungemic controls; and most of the patients in all of these groups had serum DA/cr's
3.9 µM/mg/dl. In contrast, the 10 patients with C. glabrata fungemia had initial and peak serum DA/cr's lower than those observed for patients infected with any other individual species, and most of these patients had serum DA/cr's <3.9 µM/mg/dl (Table 1). Compared to the 65 patients whose fungemias were caused by a DA-producing species (C. albicans, C. tropicalis, or C. parapsilosis), the 10 C. glabrata-infected patients had lower peak serum DA/cr's (3.6 ± 3.4 versus 9.1 ± 10.7 µM/mg/dl [means ± SD]; P = 0.003), and they were also less likely to have a peak serum DA/cr
3.9 µM/mg/dl (4/10 [40%] versus 53/65 [82%]; P = 0.009). Lastly, when the values for the 10 patients with C. glabrata fungemia were excluded, the peak and initial DA/cr values among the 73 remaining patients were
3.9 µM/mg/dl for 59 (81%) and 37 (51%) patients, respectively.
Since the fungemic patients in this study had a broad range of underlying diseases and conditions, we correlated the presence or absence of high serum DA/cr's with a series of host and microbial characteristics. Patients with cancer were less likely than patients without cancer to have high serum DA/cr's; but there were no significant correlations between a high serum DA/cr and persistent fungemia, a Charlson comorbidity score
3, prior abdominal surgery, administration of antifungal prophylaxis, infection with a Candida strain that was resistant to fluconazole, treatment with corticosteroids or other immunosuppressive drugs, neutropenia, the presence of an indwelling intravenous catheter, or treatment in community rather than teaching hospitals (Table 2).
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TABLE 2. Factors or conditions associated with elevated serum DA/cr levels
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3.9 µM/mg/dl. The serum DA/cr was
3.9 µM/mg/dl 1 or more days before the first positive blood culture was drawn in 30 patients (36%), on the same day that the first positive blood culture was drawn in 22 patients (27%), and 1 or more days after the first positive blood culture was drawn in 11 patients (13%) (Fig. 1). Twenty patients (24%) never had high serum DA/cr's.
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FIG. 1. Cumulative proportion of fungemic patients with a high serum DA/cr. The serum DA/cr was first 3.9 µM/mg/dl before or on the same day the first positive blood culture was drawn (day 0) in most of the patients with Candida fungemia. The serum DA/cr was always <3.9 µM/mg/dl in 20 (26%) fungemic patients.
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FIG. 2. Serum DA/cr and outcome. The median DA/cr declined into the normal range in the 43 patients who survived for 30 days after the onset of fungemia but not in the 40 patients who died. Day 0 was the day the first positive blood culture was drawn. The table shows how many serum samples were analyzed per group on each day and the P values for the difference between the two groups, as determined by the Mann-Whitney test.
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3.9 µM/mg/dl in any of these late specimens than if all of these late serum DA/cr's were normal (Table 3). |
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TABLE 3. Serum DA/cr values and mortality
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Our analysis of the sensitivity of serum DA/cr analysis as an initial diagnostic method showed that 63 of 83 (76%) patients with Candida fungemia and 25 of 30 (83%) patients with persistent fungemia had at least one serum DA/cr
3.9 µM/mg/dl (mean + 3 SDs of the value for healthy hospital workers). These results were very similar to those reported by Walsh et al. (16), who found that 31 of 42 (74%) neutropenic cancer patients with Candida fungemia and 25 of 30 (83%) patients with persistent Candida fungemia had one or more serum DA/cr's
4.0 µM/mg/dl (mean + 3 SDs of the value for healthy blood donors). When we analyzed the serum DA/cr's for a series of subgroups, the only significant correlations we found were that high serum DA/cr's were more frequent (i) in patients infected with the DA-producing species C. albicans, C. tropicalis, and C. parapsilosis than in those infected with the DA-nonproducing species C. glabrata (Table 1) and (ii) in patients who did not have cancer than in those with cancer (Table 2). The overall similarity of our results to those observed previously for neutropenic cancer patients and other high-risk groups (6, 8, 16) and the fact that none of the subgroups that we examined was less likely than cancer patients to have high serum DA/cr's imply that serum DA/cr measurements are as sensitive for the initial diagnosis of Candida fungemia in unselected patients with a broad range of underlying diseases and conditions as they are for the initial diagnosis of Candida fungemia in the special populations in which they have previously been studied.
Since the usefulness of any diagnostic test depends on its specificity as well as its sensitivity, we also measured the serum DA/cr's for 100 hospitalized control patients in whom blood cultures that were performed for suspected infection did not yield Candida. The nonfungemic controls had higher mean serum DA/cr's and were more likely than the 30 healthy adults to have a DA/cr
3.9 µM/mg/dl, but these differences were not quite significant (Table 1). Previous investigators have also reported that hospitalized controls with proven or suspected infections had higher serum DA concentrations or DA/cr's than healthy subjects (6, 8, 16). For example, 28 of the 206 (14%) nonfungemic controls studied by Walsh et al. (16) had serum DA/cr's
4.0 µM/mg/dl. It is not known why hospitalized patients without evidence of serious Candida infections have higher serum DA/cr's than healthy subjects. Another group has reported that the high serum DA/cr results among nonfungemic controls patients were associated with rapidly deteriorating renal function, particularly when it was associated with preterminal, multiorgan failure (16); and 4 of the 11 nonfungemic controls in the present study who had high serum DA/cr's had multiorgan failure with deteriorating renal functions. Another possibility is that the antibiotics given to many hospitalized patients may deplete the gastrointestinal tract of the bacteria that ordinarily catabolize the DA derived from the diet or from colonizing Candida organisms. This is supported by our earlier observations that (i) rats receiving dietary DA had higher serum and urinary DA levels than rats given no dietary DA and (ii) antibiotics increased the serum and urinary DA levels in rats maintained on diets that contained DA, but not in controls receiving no dietary DA (19). Lastly, it is known that approximately one-half of patients with serious invasive Candida infections have repeatedly negative blood cultures (1); thus, it is possible that some of the nonfungemic controls in this and also earlier studies had high serum DA/cr's because they had significant Candida infections that were not detected by standard diagnostic methods.
When we compared the dates on which our patients' serum DA/cr's were first
3.9 µM/mg/dl with the dates on which the first positive blood culture were drawn, we found that the serum DA/cr was first
3.9 µM/mg/dl 1 or more days before the first positive blood culture was drawn in 36% of the patients, on the same day the first positive blood sample positive by culture was drawn in an additional 27% of the patients, and 1 or more days after the first positive blood culture was drawn in an additional 12% of patients (Fig. 1). Since only limited numbers of samples were available from the patients in this study, it is likely that even better results could be obtained with more frequent sampling. Nevertheless, our results were quite similar to those of Walsh et al. (16), who found that the serum DA/cr was first
4.0 µM/mg/dl before, on the same day, and after the first positive blood culture was drawn in 35%, 15%, and 50% of neutropenic cancer patients with Candida fungemia, respectively. The close similarity between our overall results and those reported by others indicates that serum DA/cr measurements are at least as sensitive, specific, and timely for the initial diagnosis of Candida fungemia in unselected patients with a broad range of underlying diseases and conditions as they are in high-risk patients, such as those with neutropenia and cancer.
Another goal of this study was to determine if the serum DA/cr could be used for prognostic purposes. Since the clinical data available for this study were obtained in retrospect by reviewing the records from many different community and teaching hospitals, the only clinical outcome variable that was available in all cases was whether or not the patient survived. Mortality within 30 days was slightly higher in patients who had high initial or peak serum DA/cr's than in patients who had normal initial or peak serum DA/cr's, but these differences were not significant. In contrast, the 30-day mortality was much higher in patients who had high serum DA/cr's 3 or more days after the onset of fungemia than in patients whose serum DA/cr's were all normal 3 or more days after the onset of fungemia (67% versus 17%; P < 0.001). An earlier study showed that the serum DA/cr correlated with the therapeutic responses to antifungal treatment in neutropenic cancer patients and that trends in the serum DA/cr over time correlated with mortality (16). However, that earlier study did not show that the serum DA/cr on any day had clear prognostic implications. Our results are also consistent with the strong correlations previously observed between the serum DA/cr and the fungal load in untreated and treated animals with experimental candidiasis (15, 17). Because we had only retrospective clinical data, it was not possible to determine if patients with better or poorer prognoses could have been differentiated as well as or better by the use of alternative clinical or other laboratory criteria as they were from their serum DA/cr's. Nevertheless, our findings suggest that serial DA/cr measurements may be useful for identifying patients with a poor prognosis who may benefit from alternative antifungal drugs, higher drug doses, and/or combination therapy. Serial DA/cr measurements may also be useful as a surrogate marker for therapeutic responses in comparative treatment trials.
In summary, this population-based study of unselected patients with Candida fungemia showed that serum DA/cr measurements are as sensitive, specific, and timely for the initial detection of Candida fungemia in patients with a broad range of underlying diseases and conditions as has previously been reported in cancer patients and other special populations. In addition, the serum DA/cr's determined 3 or more days after the onset of fungemia correlated well with the 30-day mortality. We conclude from these results that serum DA measurements are more broadly applicable than has previously been appreciated, both for the initial diagnosis of serious Candida infections and for prognostic purposes.
We thank the laboratory personnel in all of the participating Connecticut hospitals for their assistance with collecting, saving, and storing the Candida isolates and serum specimens. R. Hajjeh and colleagues at the Centers for Disease Control and Prevention assisted with the handling and analysis of the extensive clinical database that was assembled for this study, and they also determined the species of all of the Candida isolates and tested these isolates for antifungal drug susceptibility. Vivian Wu provided valuable technical assistance.
Published ahead of print on 6 September 2006. ![]()
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