Microbiology Test

Serum Bactericidal Test

Dr. Nithin Jayan
Medically Reviewed by Dr. Nithin Jayan, MBBS, DNB
Last Updated on Apr 18, 2014
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Test : Serum Bactericidal Test

Indications : The SBT is ordered to determine the maximum bactericidal dilution of serum after the administration of antibiotics.

Prior to the test, it is important to inform the doctor about any medication that you may be taking. Blood is drawn through venipuncture, mostly from the forearm of the person.

Blood is collected from the patient in order to obtain 1 ml of serum .If the serum is collected in a different place it should be transported as quickly as possible under sterile conditions and not be refrigerated.

If the sample is collected onsite then it must be a PEAK specimen, collected in an SST tube in the following manner -

30 minutes after I.V administration of antibiotics
1 hour post I.M. administration of antibiotics
1-2 hour after oral dose of antibiotics
TROUGH specimen taken before the next dose of antibiotic

Physiology : Serum bactericidal titer (SBT) test is employed to determine the effect of anti-microbial treatment in a patient.

The test helps to estimate the dilution of bacteria in the serum and in determining the efficacy of treatment, especially in patients with conditions like endocarditis and osteomyelitis. However, the assay may not be indicative of a cure.

Endocarditis is a heart condition characterized by inflammation of the heart muscles, valves and lining of the heart. The most common cause of endocarditis is bacterial infection. Osteomyelitis, on the other hand, is a bone infection caused by infectious bacteria. It is characterized by pain at site of infection, swelling in the ankles and joints, fever and discomfort.

Normal Range : Peak bactericidal activity should be observed at >1:8 dilution, trough at >1:2.

Interpretation : Normal - Optimal treatment indicator

Peak bactericidal activity should be observed at >1:8 dilution
Trough bacterial activity should be observed at >1:32.

Sample : Peak and trough serum from patient and bacterial isolate causing infection.

Test Method : Serial dilution of patients serum with Mueller Hinton broth.

Related Tests : Antibiotic level

References : +



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