It was a bright day. You reached the ICU ward and introduced yourself to the resident there.You got ready with cap and mask and asked to take vitals of patient.
"He developed a spiking fever, and the central venous catheter was removed on day 14 of treatment. Fever is not responding to antibiotics, Sir." said one resident to the consultant.
"Send the blood for culture and inform me." said the consultant.
"Dr. Kesh , Can you arrange the items for sampling and fill up the laboratory forms?" the senior resident looks at you.
"Yes, Sir." Says you excited to know and expand your knowledge about blood culture.
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5.1 BLOOD CULTURES:
INDICATION FOR BLOOD CULTURE:
1.Where the possibility of septicemia or bacteremia is
suggested by the presence of fever,shock or other signs and symptoms occurring
in association with a known or suspected local infection such as sepsis in a
surgical wound ,Osteomyelitis,peritonitis,Arthritis,Enteric fever.
2.Pyrexia of unknown origin (temperatures of >38.3°C
(>101°F) on several occasions with fever of >3 weeks and failure to reach
a diagnosis despite 1 week of inpatient investigation)
3.Unexplained leucocytosis or leucopenia
4.Suspected fungemia specially in Immunocompromised
patients, HIV patients.
STEPS:
I)Obtain consent
II)Hand washing
III)Arranging items for sampling (MATERIALS REQUIRED)
·
70% isopropyl alcohol swabs
·
10%
Povidone iodine swabs
·
dry cotton
·
Sterile gloves of suitable size
·
2 syringes (adult: 20 cc, paediatric: 5 cc)
·
2 needles (adult: 22 gauge or preferably larger
butterfly or standard needle; paediatric: 25- or 23-gauge butterfly or standard
needle)
·
Blood culture bottle (Aerobic and anerobic)
IV) vein selection
• Arterial vs venous blood
• Indwelling arterial or venous lines
• Central or peripheral
V)Hand washing and Gloving
VI)Preparation of a skin
VII)Venepuncture and drawing a blood sample
VIII)Inoculating in blood culture bottle and shake the
bottle
IX)Labelling, storing and documenting
• Ask the patient about allergies to iodine.
• Apply the tourniquet, select the site.
(Be careful that the ends of the tourniquet do not fall
onto the puncture site, thereby contaminating it, if the tourniquet does
accidentally touch the prepared puncture site, the site must be recleaned)
• Apply alcohol/acetone pad at the puncture site for 30
seconds till it dry.
• Apply the iodine swab, apply to puncture site, move the
iodine in concentric circles outward. Keep it for 60 seconds (till it dry).
• Again, clean the site with alcohol/acetone and allow it to
dry.
• Perform the venepuncture, following routine venepuncture
procedures. Do not repalpate the site.
• If the blood culture is one of a series of samples to be
drawn from a patient, the blood culture must be collected first.
• Withdraw needle from vein and insert into the top of the
blood culture container.
(Other than syringe and needle, by closed system,
consisting of vacuum bottle and double needle collection tube can be done.)
• Do not change the needle.
• Do not hold the container in your hand, this may result in
a needle exposure.
• Do not push the blood. Mix the content. (An adequate
space above broth ensures that blood is not injected under undue pressure and
some air is still available for strict aerobes)
• Keep at room temperature.
• Label the blood specimen collected, following standard labelling
procedures. Be sure to include the site used and the number of the specimen in
the series ordered.
Blood Cultures should NOT be taken from the following
sites
•
Veins which are immediately proximal to an
existing peripheral IV cannula.
•
A femoral vein due to difficulty in skin
disinfection of the site. This area poses a high risk of contamination.
•
Catheter drawn blood cultures are equally likely
to be truly positive (associated with sepsis), but more likely to be colonized.
(One drawn through catheter and other drawn through vein PPV
of 96%)
VOLUME OF BLOOD drawn is the single most
important factor influencing sensitivity
• For adult: minimum 10 ml
• For infant and
children: 1-5 ml
1-2 ml= neonate
2-3ml= 1 month - 2year
age
3-5ml= Older children
• 20 ml of blood
obtain in sequence is more effective and sensitive (98%) specially in
intermittent bacteremia.
• Patients who have
received antibiotics should give 3 separate collections of blood. Also, one or
two of which on 2nd day also.
TIMING OF BLOOD CULTURE
• Before starting antimicrobial therapy
• At the time of fever peak
• Minimum 30-60 minute
interval between 2 samples except in critically ill septic patient.
• In continous
bacteremia-timing of blood culture is not important, but in intermittent
bacteremia 2 or 3 culture should be spaced an hour apart.
TEST PERFORMED AFTER SAMPLE REACH TO LABORATORY
Blood to broth ratio: 1:5 only, should not be <1:5 or
> 1:10
• Agitation during incubation
- Length of
incubation: • Not more than 7 days • 5 days is sufficient • >5
day-contaminants • 7 days is useful for: • Fungemia • Bacteremia due to
fastidious organisms like HACEK group, brucella, legionella • For patients
suspected of endocarditis who has been treated with antimicrobial before
obtaining blood culture • Mycobacterial culture > 4 weeks
• Atmosphere of incubation: aerobic and anaerobic
ASK YOUR MICROBIOLOGICAL DEPARTMENT TO HELP YOU IN
SELECTION OF BROTH :
• Glucose broth: useful in endocarditis
• Bile broth: In enteric fever
• Trypticase soy broth (inhibits Neisseria and S.pneumoniae)
• Brain heart infusion broth: multipurpose broth
• Thioglycolate broth: for anaerobes
• Columbia or brucella broth
• Mycobacteria: Middlebrook 7H9 with 0.05% SPS, BHI with 0.5
% polysorbate 80
• Fungus broth
Additives in broth: • Anticoagulant- bacteria are trapped
in blood clot • Antimicrobial- if patient is already in antibiotics •
Anticomplementry agents- to inactivates complement action • Antiphagocytic
Type of blood
culture bottle (AEROBIC AND ANAEROBIC CULTURE BOTTLE)
• Standard aerobic bottles- most common bacterial pathogens,
including aerobes, facultative anaerobes and for candidemia
• Smaller bottles are used for neonates and young children
• After inoculation, bottles are incubated aerobically.
SIGNS OF BACTERIAL GROWTH:
• Macroscopically:
-Generalized turbidity
-Hemolysis
- Gas production
- Discreate colonies on the surface of the sedimented red
cells
-recoverable bacterial growth may occur before turbidity is
evident.
Subculture from bottles as a routine
• For subculture:
- Subcuture should be done at least once during the first
day after 5-6 hours and at interval thereafter which should be at least twice
during first 2-3 days.
• Gram stain: Should be made and examined at the subculture
stage. Any positive finding should be reported at once to clinician as the
morphological type of organism may guide the physician to start antibiotic.
• Quantitative counts of bacteria in blood: Inoculate
1 ml amounts of blood into several tubes of melted agar and make pore plates
either directly from patients. Another method is treat the patient sample with
lytic agent. Then lysed sample is centrifuged and harvested organism cultured
directly on a suitable solid medium to allow identification and to give a
semi-quantitative indication of its presence in blood. (When monitoring
colonization associated with a prosthesis or catheter)
INTERPRETATION OF POSITIVE BLOOD CULTURE REPORT:
1. Whether true or contaminant (ASEPSIS, ASSES RISK FACTOR
PRESENT IN PATIENT)
2.FIND THE SOURCE
3.DETERMINE THE NEED FOR TREATMENT (whether patient is toxic
and in shock)
4.ADDRESS UNDERLYING INFECTIOUS FOCUS
5.LOOK FOR PATHOGEN SPECIFIC FACTORS DURING ANTIBIOTIC
TREATMENT (Toxins that are produced)
6.HELPS IN IDENTIFYING OTHER RISK FACTOR WITH INFECTION (The identification of S.bovis organism also prompted the ultimate identification of colonic carcinoma,
which is an underlying risk factor for S. bovis bacteremia)
7.LOOK FOR REASON OF IMMUNOCOMPROMISED STATE (Rule out malignancy or HIV as bactremia may be a result of oppurtunistic infection)
Therefore,clinical examination is of utmost important. As positive blood culture is not a disease in itself. It may be a result of underlying disease or part of complication.
After starting treatment, document the blood culture
clearance duration.
SOME DEFINITIONS:
Bacteremia – presence of bacteria in blood stream.Some
conditions have a period of bacteremia as part of the disease process
(ex. Meningitis, endocarditis)
Septicemia – bacteremia plus
clinical signs and symptoms of bacterial invasion and toxin production
Transient bacteremia lasts for minutes or a few hours and most
frequently occurs after manipulation of nonsterile body sites—for
example, during dental procedures; after gastrointestinal biopsy; after
percutaneous catheterization of the vascular system, bladder, or common
bile duct; and after surgical debridement or drainage—that is, after
procedures involving contaminated or colonized skin and/or mucosal
surfaces are performed and also at the onset of acute bacterial
infections.
Intermittent bacteremia is defined as bacteremia due to the
same microorganism that is detected intermittently in the same patient
because of a cycle of clearance and recurrence. Intermittent bacteremia
is often associated with undrained closed-space infections, such as
intra-abdominal or soft-tissue abscesses, and may also occur in patients
with liver abscesses, cholangitis, and focal infections, including
pneumonia, osteomyelitis, and spondylodiscitis.
Persistent bacteremia is
a characteristic of infective endocarditis (IE) and other intravascular infections, such as vascular-graft infection, a
mycotic aneurysm, or an infected thrombus. Persistent bacteremia also
occurs during the early stages of systemic bacterial infections, such as
brucellosis and typhoid fever.
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After labelling the sample, storing and documentation, you went to ICU again. Taking vitals and documenting it in files. Feeling happy to learn about blood culture.
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HAPPY STUDYING !
UPASANA Y. AND JAY
