<xsd:element name="Substance" minOccurs="0" maxOccurs="unbounded">
    <xsd:complexType>
        <xsd:sequence>
            <xsd:element name="SubstanceType" type="SubstanceTypeType">
                <xsd:annotation>
                    <xsd:documentation>Name of the substance being tested for.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element name="ThresholdLevel" type="xsd:string" minOccurs="0">
                <xsd:annotation>
                    <xsd:documentation>The defined concentration of an analyte in a specimen at or above which the test is called positive and below which it is called negative. This concentration is usually significantly greater than the sensitivity of the assay.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
            <xsd:element name="DetectionLimit" type="xsd:string" minOccurs="0">
                <xsd:annotation>
                    <xsd:documentation>Lowest concentration of a drug that can be reliably detected.</xsd:documentation>
                </xsd:annotation>
            </xsd:element>
        </xsd:sequence>
    </xsd:complexType>
</xsd:element>