Medical Lab technologist

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A*O Titre (Antistreptolysin O Test)
1. Objective:
The objective of this test was to detect and measure antistreptolysin O (A*O) antibodies in the patient’s serum, which indicated a recent or past infection with Streptococcus pyogenes.
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2. Principle:
The principle of the A*O test was based on the neutralization reaction.
Streptococcus pyogenes produces streptolysin O, a hemolytic toxin. The patient’s serum may contain antibodies (A*O) that neutralize streptolysin O, preventing it from lysing red blood cells. The degree of neutralization correlates with the concentration of A*O antibodies in the serum.
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3. Materials:
• Patient’s serum sample
• Streptolysin O reagent
• Sheep or human red blood cells (RBCs)
• Standard control sera (positive and negative)
• Test tubes or microtiter plate
• Incubator (37°C)
• Pipettes and micropipette tips
• Timer
• Water bath (optional, for precise temperature control)
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4. Procedure (Microscopic / Tube Observation):
1. Patient serum was serially diluted in test tubes or microtiter wells.
2. Streptolysin O reagent was added to each diluted serum sample.
3. The mixture was incubated at 37°C for 1–2 hours to allow antibody–antigen interaction.
4. Washed sheep or human RBCs were added to the tubes.
5. Tubes were incubated again to allow hemolysis.
6. The degree of hemolysis or lack of hemolysis was observed.
7. The highest dilution showing complete neutralization of hemolysis was recorded as the A*O titre.
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5. Result:
• Positive: Elevated A*O titre indicated a recent or ongoing streptococcal infection, commonly associated with rheumatic fever, post-streptococcal glomerulonephritis, or pharyngitis.
• Negative: Low or absent A*O titre indicated no recent streptococcal infection.
• Reference values varied by age and laboratory, but a titre >200 IU/mL in adults was generally considered significant.
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6. Uses:
• It was used to diagnose post-streptococcal complications such as rheumatic fever and glomerulonephritis.
• Assisted in confirming recent streptococcal infections.
• Useful in epidemiological studies of streptococcal infections.
• Monitored treatment response in streptococcal-related diseases.
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7. Consultation:
Patients with a high A*O titre were advised to consult a physician or pediatrician/rheumatologist for further evaluation. Additional clinical assessments, throat swab cultures, and monitoring for cardiac or renal complications were recommended depending on the clinical scenario.

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