Clinics and Departments

Laboratory Services

Lab Dept:


Test Name:


General Information

Lab Order Codes:



Bactericidal Titers; Cidal Titer; Serum Bactericidal Titer; Serum Inhibitory Titer; SBT (Serum Bactericidal Titer)

CPT Codes:

87197 – Serum bactericidal titer (Schlicter test)

Test Includes:

Includes the killing capacity of the patient’s serum or body fluid against the patients infecting organism.


Test Indications:

Determines the killing capacity of the patient’s serum or body fluid against the patients infecting organism.

Lab Testing Sections:


Referred to:

Mayo Medical Laboratories (MML Test: 8075)

Phone Numbers:

MIN Lab: 612-813-5866

STP Lab: 651-220-6555

Test Availability:

Daily, 24 hours

Turnaround Time:

3 days

Special Instructions:

● Both the infecting bacteria and serum are required for this test.
● To reduce turnaround, notify Microbiology Laboratory prior to specimen collection so a fresh isolate of the infecting organism can be prepared.
Specimen site and date/time of collection are required for specimen processing.
● Wait until patient has been on therapy for 48 hours.
● Indicate if the specimen is a Peak or Trough specimen, antibiotic therapy, date and time of last dosage, and method of administration.


Specimen Type:



Red top (plain, no gel) tube or sterile container


6 mL (Minimum: 5 mL) blood

Processed Volume:

1.3 mL (Minimum: 0.5 mL) serum


Peak level: Draw 30 - 40 minutes after completion of intravenous administration of antibiotic, 1 hour after intramuscular dose, or 1-2 hours after oral dose.

Trough level: Draw just before next dose.

The serum specimen must be drawn aseptically. Any bacterial contamination from the skin may interfere with the results.

If the patient is receiving more than one antibiotic, the serum is drawn at the lowest and highest concentrations of the combined antibiotics. Multiple dosage schedules may require consultation with pharmacy for optimal collection time.


Venipuncture for patients less than 2 months of age: Prep with 2% tincture of iodine.

1. Scrub venipuncture site with 70% alcohol for 1 min using the Frepp® applicator. Allow to dry.
Using the Sepp® applicator, apply 2% tincture of iodine to site starting at the center and moving outward in concentric circles. Allow to dry.
If the site must be touched during venipuncture, disinfect the gloved fingers.
Collect 6 mL of blood in a red top tube.
Transport to the lab immediately.

Venipuncture for patients more than 2 months of age: Prep with CloraPrep Sepp® Applicator.

1. Break the Sepp® ampule to release the 2% CHG.
Apply the CloraPrep solution using a back-and-forth friction scrub for 30 seconds.
Allow the area to dry for 30 seconds.
If the site must be touched during venipuncture, disinfect the gloved fingers.
Collect 6 mL of blood in a red top tube.|6. Transport to the lab immediately.

Line Draw

1. Prep catheter port with 2% tincture of iodine/betadine followed by 70% alcohol and allow to dry.
Aseptically collect 6 mL of blood through the injection port. Blood may be collected without first drawing a discard.
Transfer into a red top tube.


Transport to the Microbiology Laboratory immediately at room temperature.

Special Processing:

1. Spin down blood and send 3 mL of serum in a sterile screw-capped tube.
Freeze aliquot until it can be shipped. Ship frozen.
An agar slant of the patient’s isolate must accompany the serum. Agar plates are not acceptable. Send in an “Infectious Material” container supplied by Mayo.


Transport to the Microbiology Laboratory immediately at room temperature. Store serum frozen.

Sample Rejection:

Specimen with a transit time exceeding 1 hour after collection; specimen not submitted in appropriate transport container; improperly labeled specimen; insufficient volume; external contamination. If an unacceptable specimen is received, the physician or nursing station will be notified and another specimen will be requested before the specimen is discarded.


Reference Range:

● Bacteriostatic or inhibitory titers ≥1:16 usually signifies adequate dosage.
● Bactericidal titer ≥1:8 should be obtained, except in cases of staphylococcal endocarditis where titers of 1:32 may be optimum.
● The SBT measures the combined activity of all antimicrobial agents present at the time of serum collection.


This test determines bactericidal levels in blood but its usefulness in evaluating treatment of infection sites outside the bloodstream is not clear. The serum bactericidal test (SBT) does not account for the contribution of the immune system in combating infection. After collection of a specimen, during the clotting process, platelets release bactericidal proteins that may alter results in vitro. This test might suggest an adequate therapeutic level, but would give no clue to potential toxicity when an extremely narrow margin exists between a therapeutically adequate dose and a possible toxic one (e.g., aminoglycosides). The bactericidal activity is only one factor in the treatment of infected patients. It is important to realize the difference between bacteriologic cure and clinical outcome. The ultimate clinical outcome cannot be predicted accurately by an in vitro test of antimicrobial activity.


Inhibitory Titer and Bactericidal Titer


Mayo Medical Laboratories Web Page August 2005

Cook, JH, and M Pezzlo (1992). Specimen receipt and accessioning. Section 1. Aerobic bacteriology, 1.2.1-4. In HD Isenberg (ed) Clinical Microbiology Procedures Handbook. American Society for Microbiology, Washington DC

Miller, J Michael (1999) A Guide To Specimen Management in Clinical Microbiology, American Society for Microbiology, Washington DC

Miller, J Michael, and HT Holmes (1999) Specimen Collection, Transport, and Storage In PR Murray et al, (ed), Manual of Clinical Microbiology, 7th edition, American Society for Microbiology, Washington DC, pp 33-104


8/13/2005: Test moved from Fairview Diagnostic Laboratories to Mayo Medical Laboratories. CSF and Fluid specimens are no longer acceptable for this procedure.

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