Interpret the following ASO results: Tube Nos. 1-4 (Todd unit 125): no hemolysis; Tube No. 5 (Todd unit 166): hemolysis.

The interpretation of the ASO (antistreptolysin O) results indicates that the sample is considered positive for the Todd unit of 125. In the context of the ASO test, hemolysis typically signifies the presence of antistreptolysin O antibody in the serum.

In this case, Tubes 1-4 showed no hemolysis, suggesting that concentrations of the antistreptolysin O antibody present in those tubes were not high enough to cause hemolysis, corresponding to a Todd unit of 125. However, Tube 5 demonstrated hemolysis at a higher Todd unit of 166, indicating that the antibody concentration exceeded the threshold necessary to produce hemolysis, thus confirming that the patient has a clinically significant level of antistreptolysin O.

By identifying the highest title at which no hemolysis occurs, which is 125, it is concluded that this represents the significant antibody level. It is important to note that positive ASO results are usually reported based on the highest dilution before hemolysis occurs, and hence the interpreting of a result at 125 as positive is appropriate in this context.