Why in this lab test results the microsomal antibodies amount has less sign and thireoglobulin antibodies don't have this sign? I did not question it first but now I have suspicion may be I am not getting it correctly. There is some ambiguity.
Measurements will always have measurement errors, we distinguish between systematic errors and statistical errors due to noise, or other random effects than on average are zero. Usually the former type of error should not be in play, the tests will have been designed such that on average the tests results are correct. The latter type of error is always in play, this leads to an error margin that typically gets worse at lower measured values. This means that there will always exist a lowest cutoff value such that measurement values below it will be consistent with a real value ranging from zero up to the cutoff. This will then be reported like your value for the microsomal antibodies. For values that are a bit higher than the cutoff, the protocol will be to report the measured value, but the measurement error may still be significant.