International Screening Limits-Plasma
Definition and Recommendations for their Application in the Control of
Therapeutic Substances

Substances prohibited in racing are defined in Clause 10 of Article 6A of the International Agreement on Breeding, Racing and Wagering; accordingly therapeutic substances used for the treatment of racehorses are covered within this definition and prohibited by the rules of racing at all concentrations. In order for laboratories to report the presence of certain therapeutic substances in a consistent manner, International Screening Limits (ISLs) have been agreed for these substances.

The ISL is the urine or plasma concentration adopted for the screening of a specified therapeutic prohibited substance; it is derived from administration studies followed by a risk analysis consisting of two components: a risk assessment (evaluation of the effect of the substance and factors related to its control) and a risk management (decision step for harmonisation).  ISLs are harmonised detection limits agreed following input by international consensus and are conveyed by instruction from racing authorities to their laboratories.  The ISLs are simply the detection limits to be used by the laboratories when screening for certain therapeutic substances as instructed by the authorities; they are not international thresholds.  When the screening procedure indicates the ISL, in either urine or plasma, has been exceeded, all that is required is qualitative confirmatory analysis (usually by mass spectrometry) to confirm the presence or absence of the prohibited substance. Quantification is not required.

The ISL need not be applied in the event of the detection of two or more pharmacologically-related therapeutic substances, or any such substance and a diuretic, in an official sample.

Article 6A, Clause 19 of the International Agreement on Breeding, Racing and Wagering states the aim of signatory countries is that their laboratories should control the detection of legitimate therapeutic substances through the application of internationally harmonised screening limits which have been recommended by the IFHA’s Advisory Council on Equine Prohibited Substances and Practices and selectively adopted by the relevant signatory countries.

Thus, ISLs are voluntary decision limits and may not be adopted by all countries in which horseracing occurs. Additionally, substances that are not subject to ISLs are treated differently based upon the rules of racing in effect in a specific Horseracing Authority as well as the laboratory’s limits of detection. It is the responsibility of the connections of a horse to determine the applicable rules of racing in the jurisdiction in which they are racing.

International Screening Limits and signatory countries