Anticoagulant Carryover May Influence Clot Formation in Direct Tube Coagulase Tests from Blood Cultures

Varettas, Kerry; Mukerjee, Chinmoy; Taylor, Peter

doi:10.1128/jcm.43.9.4613-4615.2005

Cited by 15 publications

(12 citation statements)

References 17 publications

(7 reference statements)

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“…The reported sensitivities of 34% at 2 h of incubation and 65% at 4 h of incubation (7) are considerably lower than those previously described and suggest an unacceptably high rate of false negatives (1,4,5,6,8,9,11). The authors draw the conclusion that despite its low sensitivity the DTC test is clinically valuable, particularly in experienced hands, because of its low cost and simplicity (7).…”

contrasting

confidence: 44%

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

Lagacé-Wiens¹,

Alfa

Manickam

et al. 2007

J Clin Microbiol

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ᰔIn a recent edition of the Journal of Clinical Microbiology, Qian et al. described the sensitivity and specificity of the direct tube coagulase (DTC) test for the presumptive identification of Staphylococcus aureus directly from positive blood culture bottles from which Gram stains were consistent with staphylococci (7). The reported sensitivities of 34% at 2 h of incubation and 65% at 4 h of incubation (7) are considerably lower than those previously described and suggest an unacceptably high rate of false negatives (1,4,5,6,8,9,11). The authors draw the conclusion that despite its low sensitivity the DTC test is clinically valuable, particularly in experienced hands, because of its low cost and simplicity (7).However, Qian et al. neither evaluated nor commented on the use of the thermostable DNase test for the presumptive identification of S. aureus directly from positive blood culture bottles, as described by Madison and Baselski (4) and others (1,6,8,9,10). In these studies, the thermostable DNase test has been reported to be sensitive (85% to 100%) and specific (93 to 100%), to have a high degree of correlation with the DTC test (92.7 to 100%), to be relatively simple to perform, and to have low material cost (1,4,6,8,9,10). In our laboratory, the material cost per test is 79¢, compared to 22 ¢ for the DTC test. Furthermore, the thermostable DNase test has the advantage of having a more rapid turn-around time than the DTC test, often being positive at 1 h (4, 8).We recently compared the thermostable DNase test with the DTC test for the presumptive identification of S. aureus from BacT/Alert (bioMérieux, Marcy l'É toile, France) blood culture bottles in two tertiary-care teaching hospitals over a period of 50 days. The DTC test was performed by mixing 50 l of positive blood culture broth with 450 l of rabbit plasma (Becton Dickinson, Oakville, Ontario, Canada) in a glass test tube and incubating at 37°C. The thermostable DNase test was performed using the agar diffusion method. A 2-ml aliquot of blood culture broth was boiled for 15 min and then cooled to room temperature. Six-millimeter holes were cut in toluidine blue DNase agar plates produced in-house according to the method described by Lachica et al. (3), and 100 l of the boiled blood culture broth was placed into the well and then incubated at 37°C. Positive and negative controls were used in all tests. Tests were read at 2 and 4 h. Sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) were calculated according to the method of Elder (2). Of 81 positive blood culture bottles from unique patients with initial Gram stains showing gram-positive cocci in clusters, the DTC test demonstrated a sensitivity of 56.7% at 2 h and 93.3% at 4 h while the thermostable DNase test had a sensitivity of 96.7% at 2 h and 100% at 4 h ( Table 1). The specificity for both methods was 100% at both 2 and 4 h.Based on our findings, we propose that although the DTC test used with BacT/Alert blood culture bottles has an acceptabl...

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contrasting

confidence: 44%

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

Lagacé-Wiens¹,

Alfa

Manickam

et al. 2007

J Clin Microbiol

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“…After centrifugation at 2000 g for 10 min, the supernatant was discarded and 1 mL of citrate rabbit plasma was added to the remaining pellet of bacteria and vortexed briefly. For DTCTs using saline dilution (SDT), a 1:10 dilution of blood culture broth in saline was made [20]. After brief vortexing, four drops (0.1 mL) were added to 1 mL of rabbit plasma.…”

Section: Sensitivity (S) Specificity (Sp) Positive Predictive Valumentioning

confidence: 99%

Performance of two tube coagulase methods for rapid identification of Staphylococcus aureus from blood cultures and their impact on antimicrobial management

Sturm

Kwa

Vos

et al. 2008

Clinical Microbiology and Infection

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Test parameters and clinical impact of the direct tube coagulase test (DTCT) for rapid identification of Staphylococcus aureus from blood culture were investigated. The sensitivity of the DTCT at 4 h using saline dilution was 96%, compared with 93% using serum separator tubes; specificity was 100% for both methods. Among 32 patients with S. aureus bacteraemia, treatment modifications were based on microbiology results from the primary source of infection in 12 patients, on a Gram's stain from blood culture in seven patients, and on the DTCT in nine patients. The DTCT is a valuable adjunct in the routine microbiology laboratory because of its good performance, technical simplicity and low cost.

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“…Although the use of new molecular methods for rapid identification of S. aureus from blood culture bottles is expanding (15, 17), detection of coagulase activity by direct tube coagulase (DTC) testing remains a costeffective, easy to perform, and reliable method for early detection of S. aureus in blood culture broth with a Gram stain result suggestive of staphylococci (10,13,16,23). Since false-negative results increase the therapeutic delay, the carryover of contaminants from either the culture broth or the patient's plasma that interfere with the tube test clotting reaction has to be avoided (23).…”

mentioning

confidence: 99%

Dabigatran Inhibits Staphylococcus aureus Coagulase Activity

et al. 2010

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The ability of Staphylococcus aureus to clot plasma through conformational activation of prothrombin by staphylocoagulase is used to distinguish S. aureus from coagulase-negative staphylococci. We show that while the direct thrombin inhibitor dabigatran inhibits staphylocoagulase activity, the clinical use of dabigatran etexilate is not expected to interfere with direct tube coagulase testing.Since the early notion, developed more than a century ago, that the ability to clot plasma correlates with the pathogenic potential of staphylococci (3,14), this phenomenon has been used to distinguish Staphylococcus aureus from less virulent, coagulase-negative staphylococci. Although the use of new molecular methods for rapid identification of S. aureus from blood culture bottles is expanding (15, 17), detection of coagulase activity by direct tube coagulase (DTC) testing remains a costeffective, easy to perform, and reliable method for early detection of S. aureus in blood culture broth with a Gram stain result suggestive of staphylococci (10,13,16,23). Since false-negative results increase the therapeutic delay, the carryover of contaminants from either the culture broth or the patient's plasma that interfere with the tube test clotting reaction has to be avoided (23).Clotting occurs when fibrinogen is converted into fibrin by thrombin. Under physiological conditions, the proteolytic activation of the inactive precursor prothrombin into thrombin is the final step in the tightly regulated coagulation cascade. Staphylocoagulase secreted by S. aureus directly binds to prothrombin to form the staphylothrombin complex and thus bypasses the coagulation cascade and its physiological regulation (6). As a consequence of this unique nonproteolytic direct thrombin activation, treatment with heparins, vitamin K antagonists, or the thrombin inhibitor hirudin does not interfere with staphylothrombin function (9) and is of no concern for DTC testing.In view of the recent availability and increasing clinical use of the new direct thrombin inhibitor dabigatran etexilate, we studied whether dabigatran inhibits staphylocoagulase and whether clinical use of dabigatran etexilate is expected to interfere with DTC testing.To test these possibilities, we measured coagulation of citrated human plasma as the change in absorbance at 405 nm (A 405 ) after the addition of purified staphylocoagulase (3 nM) in the presence of increasing concentrations (0, 0.625, 1.25, 2.5, 5, and 10 nM) of dabigatran (Boehringer Ingelheim

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Anticoagulant Carryover May Influence Clot Formation in Direct Tube Coagulase Tests from Blood Cultures

Cited by 15 publications

References 17 publications

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures

Performance of two tube coagulase methods for rapid identification of Staphylococcus aureus from blood cultures and their impact on antimicrobial management

Dabigatran Inhibits Staphylococcus aureus Coagulase Activity

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