Blood cultures - do they make a difference to patient management?


Blood cultures are an expensive test, and optimising the pathway requires considerable effort and commitment. Is it worth the trouble? We looked at 102 consecutive episodes of bacteraemia with clinical details in microbiology system, excluding contaminants and deduplicated to see how it affected patient management.

To spoil the ending, these are the conclusions :


Conclusions


A positive blood culture significantly altered management in 72/102 cases of significant bacteraemia

This was on the basis of

            Gram stain                  27 cases
            Culture                       25 cases
            Sensitivities                20 cases



There may be debate as to the proportion of septic patients who are bacteraemic (anywhere from 10% to 95% depending on what you believe), but even if we take the lower end of this as being true, bacteraemia would seem an important way of influencing management, even if it is just prompting the microbiologist to get out of the lab and go and review the patient.

Effect on diagnosis

Blood cultures had a significant impact on diagnosis in 25 cases (25%)
            In 18 cases this was predominantly on the basis of the gram stain
            In 7 cases this was predominantly on the basis of culture results

Review of incorrect diagnosis

In 15 cases the initial diagnosis was wrong and was modified on the basis of the blood culture result

            In 10 cases the diagnosis was switched on the basis of the gram stain
            In 5 cases the diagnosis was switched on the basis of the culture

Initial diagnosis when wrong

           
CAP
6
UTI
4
HAP
2
Neutropenic sepsis
1
Cellulitis
1
Endocarditis
1

Corrected diagnosis when initially wrong

UTI
5
Cryptic
2
Endocarditis
1
Infected ulcer
1
Infected prosthetic joint
1
Septic arthritis
1
Cholecystitis
1
CAP
1
Abdominal infection
1
Discitis
1


Review of uncertain diagnosis

In 10 cases, the blood culture suggested a cause of infection that was not otherwise apparent.

            In 8 cases this was suggested from the gram stain
            In 2 cases this was suggested from the culture results

Final diagnosis when initially uncertain

Line infection
3
Septic arthritis
2
UTI
1
Surgical site infection
1
Discitis
1
Cellulitis
1
Abdominal infection
1

Effect on antibiotic usage

In 47 cases when the diagnosis was supported by the blood culture, antibiotics were changed on the basis of the result and microbiologist review

Narrowed
20
Broadened
11
Switched
11
Started
5

The switch was instigated on the basis of :

gram
9
organism
18
sensitivity
20

Narrowed :

taz to amox
3
Amox/gent to amox
2
gent to amox
2
flu to amox
1
Co-amox/clari to amox
1
Mero to trim.
1
Not recorded
1
Taz to fluclox
1
mero to cipro
1
mero to mtz
1

Broadened

Metronidazole added to fluclox
2
gent r to mero
2
amox to cef
1
taz to mero - res gent taz
1
fluclox to taz
1

Switched

taz R switched to cipro
1
cef r to cip
1
taz to teic line lock
1
fluclox to amox
1


These were the organisms : 
1

Coliform
48
Other
18
Haemolytic streptococcus
11
S. aureus
9
anaerobe
6
Pneumococcus
5
Faecal streptococcus
5

These were the final diagnoses:

UTI
41
Cholecystitis
11
Cryptic
11
Cellulitis
7
CAP
6
Line infection
5
Septic arthritis
5
Abdominal infection
3
Infected prosthetic joint
2
Infected ulcer
2
Discitis
2
Infected pressure ulcer
2
Surgical site infection
1
Mycotic aneurysm
1
Endocarditis
1
SBP
1
Diverticulitis
1


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