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Uh, Jang, Park, Kim, Seo, Yoon, Choi, Kim, and Kim: Factors Influencing the False Positive Signals of Continuous Monitoring Blood Culture System
Original Article

Ann Clin Microbiol 2014;17(2):58-64.

Published online: 5 June 2014

DOI: https://doi.org/10.5145/ACM.2014.17.2.58

Factors Influencing the False Positive Signals of Continuous Monitoring Blood Culture System

Young Uh1, 2, In Ho Jang1, Soon Deok Park1, Kab Seung Kim1, Dong Min Seo2, Kap Jun Yoon1, Hee Kyoung Choi3, Young Keun Kim3, Hyo Youl Kim3

1Department of Laboratory Medicine, Yonsei University Wonju Severance Christian Hospital, Wonju, Korea

2Medical Information Development, Yonsei University Wonju Severance Christian Hospital, Wonju, Korea

3Internal Medicine, Yonsei University Wonju Severance Christian Hospital, Wonju, Korea

Correspondence: Young Uh, Department of Laboratory Medicine, Yonsei University Wonju College of Medicine, 20 Ilsan-ro, Wonju 220-701, Korea. (Tel) 82-33-741-1592, (Fax) 82-33-731-0506, (E-mail) u931018@yonsei.ac.kr

Received 6 March 201419 April 2014       Accepted 21 April 2014

Copyright © 2014 The Korean Society of Clinical Microbiology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

초록

Background

The false positive signals of a continuous monitoring blood culture system (CMBCS) in-crease the reporting time and laboratory cost. This study aimed to determine the highly relevant variables that discriminate false positive signals from true positive signals in a CMBCS.

Methods

Among 184,363 blood culture sets (aerobic and anaerobic), the signal-positive samples according to a BACTEC FX system (Plus Aerobic/F, BDA; Plus Anaerobic/F, BDN) and BacT/Alert 3D system (Standard Aerobic, BSA; Standard Anaerobic, BSN) between April 2010 and November 2013 were classi-fied into two groups: false positive or true positive signals. The data of 15 parameters between the two groups were then statistically compared.

Results

Among total blood cultures, the positive rates of CMBCS signals according to BDA, BDN, BSA, and BSN were 4.9%, 2.8%, 3.8%, and 3.2%, respectively. The false positive rates of CMBCS signals according to BDA, BDN, BSA, and BSN were 0.6%, 0.1%, 0.1%, and 0.1%, respectively. The blood volume, detection time, time interval between admission and test, C-reactive protein concentration, leukocyte count, delta neutrophil index, and mean peroxidase index showed statistically significant differences between the two groups.

Conclusion

There were no variables with diagnostic sensitivity and specificity for discriminating the two groups. Therefore, analysis of bacterial growth curves produced by CMBCS is needed for early and effec-tive detection of false positive signals.

Keywords: Blood, Culture, False positive, Monitoring, Signal

REFERENCES

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Table 1.
Number (%) of signal positive blood cultures by continuous monitoring blood culture systems
Blood culture results No. (%) of blood culture bottle
BACTEC FX system BacT/Alert 3D system
  Aerobic Anaerobic Aerobic Anaerobic
Total number 63,344 (100) 63,344 (100) 121,519 (100) 121,519 (100)
Signal negative 60,266 (95.1) 61,584 (97.2) 116,928 (96.2) 117,665 (96.8)
Signal positive 3,078 (4.9) 1,760 (2.8) 4,591 (3.8) 3,854 (3.2)
 True positive 2,739 (4.3) 1,675 (2.7) 4,437 (3.7) 3,697 (3.1)
 False positive 339 (0.6) 85 (0.1) 154 (0.1) 157 (0.1)
Table 2.
Data comparison of false positive and true positive signals obtained from BACTEC FX system and BacT/Alert 3D system by according to parameters
Parameters BACTEC FX system BacT/Alert 3D system
Aerobic Anaerobic Aerobic Anaerobic
False positive∗ True positive∗ P value AUC False positive∗ True positive∗ P value AUC False positive∗ True positive∗ P value AUC False positive∗ True positive∗ P value AUC
Gender (F/M) 145/194 1,094/1,645 0.316 47/38 688/987 0.010 NT 57/97 1,931/2,506 0.109 64/93 1,703/1,994 0.192
Age (yr) 60.5 61.2 0.761† 56.5 58.9 0.487 52.7 60.2 0.001 0.615 53.1 60.1 0.003 0.551
Blood volume (mL) 3.5 3.3 0.018 0.531 2.7 2.8 0.664† 3.0 2.1 0.000 0.584 2.9 2.2 0.001 0.545
Detection time (min) 2,448 1,553 0.000 0.660 2,241 1,773 0.072 1,830 1,559 0.108 1,961 1,470 0.002 0.541
Interval time‡ (days) 12.6 17.3 0.004 0.530 15.8 12.2 0.238† 13.2 11.2 0.432† 5.4 9.3 0.000 0.513
Entry§ (D/N) 173/166 1,384/1,355 0.863 35/50 868/807 0.059 72/82 2,170/2,267 0.623 61/96 1,852/1,845 0.007 NT
CRP (mg/dL) 6.8 9.0 0.003 0.583 9.7 8.8 0.566† 6.4 9.2 0.002 0.596 7.6 9.6 0.078
Leukocyte count (106/L) 10,181 11,490 0.019 0.564 10,054 1,160 0.176† 12,150 11,479 0.341† 14,969 11,562 0.027 0.553
Neutrophil count (106/L) 7,734 9,440 0.000 0.579 7,591 8,863 0.096† 8,327 9,213 0.127† 9,593 9,156 0.446†
LUC (%) 2.3 2.0 0.218 2.2 2.0 0.589† 2.8 1.8 0.091 4.0 1.9 0.049 0.577
DNI 1.7 4.6 0.000 0.644 2.8 4.8 0.002 0.533 3.0 4.6 0.001 0.548 4.2 5.5 0.118†
MPXI 2.4 1.7 0.037 0.576 2.9 1.7 0.079† 1.2 1.4 0.621† 2.9 1.7 0.019† 0.545
pH 7.4 7.4 0.832† 7.4 7.4 0.680† 7.4 7.4 0.326† 7.4 7.4 0.643†
PaO2 (mmHg) 96.8 99.2 0.455† 110.8 98.1 0.039† 0.630 103.4 97.7 0.170† 100.0 96.5 0.365†
PaCO2 (mmHg) 33.3 33.8 0.596† 36.1 32.4 0.019† 0.649 33.5 33.5 0.983† 32.6 32.5 0.903
Abbreviations: AUC, area under the relative operating characteristic curve; F, female; M, male; NT, not tested; D, day work time (working hours; 08:00-17:00); N, night work time (working hours; 17;00-08:00); CRP, C-reactive protein; LUC, large unstained cell; DNI, delta neutrophil index; MPXI, mean peroxidase index.

∗ Data was expressed as mean value.

† Levene test showed equal variance (P＞0.05).

‡ Time interval between admission day and request day of blood culture.

§ Entry time of blood culture bottles to continuous monitoring blood culture systems.

Table 3.
Number (%) of false positive and true positive signals obtained from BACTEC FX system and BacT/Alert 3D system according to blood volume and detection time
Parameters BACTEC FX system BacT/Alert 3D system
Aerobic Anaerobic Aerobic Anaerobic
False positive True positive False positive True positive False positive True positive False positive True positive
Blood volume (mL)
 ≤0.5 126 (7.7) 382 (14.1) 13 (15.3) 342 (20.5) 38 (24.7) 1,440 (32.6) 48 (30.6) 1,295 (35.0)
 ＞0.5-10 310 (91.7) 2,295 (84.4) 71 (83.5) 1,293 (77.6) 111 (72.1) 2,947 (66.7) 106 (67.5) 2,370 (64.2)
 ＞10 2 (0.6) 41 (1.5) 1 (1.2) 32 (1.9) 5 (3.2) 30 (0.7) 3 (1.9) 29 (0.8)
 Total 338 (100) 2,718 (100) 85 (100) 1,667 (100) 154 (100) 4,417 (100) 157 (100) 3,694 (100)
Detection time
 Day (s) 1 115 (33.9) 1,706 (62.3) 46 (54.1) 985 (58.8) 93 (60.4) 2,750 (62.0) 83 (52.9) 2,404 (65.0)
  2 120 (35.4) 732 (26.7) 14 (16.5) 395 (23.6) 26 (16.9) 1,223 (27.6) 30 (19.1) 947 (25.6)
  3 52 (15.3) 198 (7.2) 7 (8.2) 113 (6.7) 13 (8.4) 308 (6.9) 23 (14.6) 185 (5.0)
  4 31 (9.2) 61 (2.2) 9 (10.6) 104 (6.2) 8 (5.2) 109 (2.4) 6 (3.8) 90 (2.5)
  5 21 (6.2) 42 (1.6) 9 (10.6) 78 (4.7) 14 (9.1) 47 (1.1) 15 (9.6) 71 (1.9)
  Total 339 (100) 2,739 (100) 85 (100) 1,675 (100) 154 (100) 4,437 (100) 157 (100) 3,697 (100)
 Hour (s) ≤1 0 (0) 2 (0.1) 10 (11.8) 1 (0.1) 1 (0.6) 0 (0) 0 (0) 0 (0)
  ＞1-2 0 (0) 14 (0.5) 2 (2.4) 26 (1.6) 1 (0.6) 1 (0) 4 (2.5) 0 (0)
  ＞2-4 5 (1.5) 58 (2.1) 4 (4.7) 41 (2.4) 43 (28.0) 37 (0.8) 32 (20.4) 25 (0.7)
  ＞4-8 1 (0.3) 24 (0.9) 8 (9.4) 17 (1.0) 1 (0.6) 30 (0.7) 0 (0) 34 (0.9)
  ＞8-16 46 (13.6) 910 (33.2) 9 (10.6) 598 (35.7) 32 (20.8) 1,283 (28.9) 35 (22.3) 1,455 (39.4)
  ＞16-32 108 (31.8) 1,072 (39.1) 16 (18.8) 509 (30.4) 22 (14.3) 2,035 (45.9) 24 (15.3) 1,473 (39.8)
  ＞32-64 116 (34.2) 506 (18.5) 16 (18.8) 272 (16.2) 28 (18.2) 826 (18.6) 37 (23.6) 497 (13.4)
  ＞64 63 (18.6) 153 (5.6) 20 (23.5) 211 (12.6) 26 (16.9) 225 (5.1) 25 (15.9) 213 (5.8)
  Total 339 (100) 2,739 (100) 85 (100) 1,675 (100) 154 (100) 4,437 (100) 157 (100) 3,697 (100)
Table 4.
Number (%) of false positive and true positive signals obtained from BACTEC FX system and BacT/Alert 3D system according to white blood cell count
WBC count (106/L) BACTEC FX system BacT/Alert 3D system
Aerobic Anaerobic Aerobic Anaerobic
False positive True positive False positive True positive False positive True positive False positive True positive
TLC ≤1,000 15 (4.5) 92 (3.5) 2 (2.4) 58 (3.6) 0 (0) 112 (2.6) 4 (2.6) 106 (2.9)
 ＞1,000-4,000 23 (7.0) 196 (7.4) 7 (8.4) 107 (6.6) 11 (7.2) 316 (7.2) 11 (7.1) 246 (6.7)
 ＞4,000-10,000 163 (49.2) 1,059 (39.8) 38 (45.8) 665 (40.7) 65 (43.0) 1,674 (38.4) 51 (32.9) 1,410 (38.7)
 ＞10,000-30,000 125 (37.8) 1,238 (46.5) 35 (42.2) 764 (46.8) 72 (47.7) 2,170 (49.8) 81 (52.2) 1,802 (49.4)
 ＞30,000-50,000 3 (0.9) 64 (2.4) 1 (1.2) 35 (2.1) 1 (0.7) 79 (1.8) 4 (2.6) 79 (2.2)
 ＞50,000-100,000 0 (0) 10 (0.4) 0 (0) 2 (0.1) 1 (0.7) 8 (0.2) 2 (1.3) 1 (0.0)
 ＞100,000 2 (0.6) 1 (0.0) 0 (0) 1 (0.1) 1 (0.7) 2 (0.0) 2 (1.3) 4 (0.1)
 Total 331 (100) 2,660 (100) 83 (100) 1,632 (100) 151 (100) 4,361 (100) 155 (100) 3,648 (100)
TNC ≤1,000 22 (7.3) 133 (5.4) 3 (4.1) 72 (4.7) 2 (1.5) 176 (4.3) 7 (5.0) 159 (4.6)
 ＞1,000-4,000 55 (18.4) 392 (15.8) 14 (18.9) 259 (17.0) 29 (21.3) 624 (15.3) 27 (19.3) 558 (16.3)
 ＞4,000-10,000 141 (47.2) 1,098 (44.4) 35 (47.3) 693 (45.6) 52 (38.2) 1,823 (44.8) 51 (36.4) 1,510 (44.0)
 ＞10,000-30,000 78 (26.1) 804 (32.5) 22 (29.7) 479 (31.5) 53 (39.0) 1,393 (34.2) 53 (37.9) 1,164 (33.9)
 ＞30,000-50,000 2 (0.7) 43 (1.7) 0 (0) 18 (1.2) 0 (0) 52 (1.3) 2 (1.4) 37 (1.1)
 ＞50,000-100,000 0 (0) 4 (0.2) 0 (0) 0 (0) 0 (0) 6 (0.1) 0 (0) 3 (0.1)
 ＞100,000 1 (0.3) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0)
 Total 299 (100) 2,474 (100) 74 (100) 1,521 (100) 136 (100) 4,074 (100) 140 (100) 3,431 (100)

Abbreviations: WBC, white blood cell; TLC, total leukocyte count; TNC, total neutrophil count.

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