I have the following xml

       <TestRequests>
          <TestRequest CollectionStatus="Resulted">
            <Category>Allergen</Category>
            <Specimen>
              <CollectedStartDT>
                <Value>2007-02-15T05:30:00.0000000+05:30</Value>
              </CollectedStartDT>
            </Specimen>
            <Results>
              <Observation>
                <Identifier>
		  <Code>1</Code>
                  <SpecimenType>AMN</SpecimenType>
                </Identifier>
              </Observation>
              <Observation>
                <Identifier>
		  <Code>2</Code>
                  <SpecimenType>AMN</SpecimenType>
                </Identifier>
              </Observation>
            </Results>
          </TestRequest>

          <TestRequest CollectionStatus="Resulted">
            <Category>Allergen</Category>
            <Specimen>
              <CollectedStartDT>
                <Value>2007-02-15T05:30:00.0000000+05:30</Value>
              </CollectedStartDT>
            </Specimen>
            <Results>
              <Observation>
                <Identifier>
 		<Code>3</Code>
                  <SpecimenType>BIFL</SpecimenType>
                </Identifier>
              </Observation>
            </Results>
          </TestRequest>


          <TestRequest CollectionStatus="Resulted">
            <Category>Allergen</Category>
            <Specimen>
              <CollectedStartDT>
                <Value>2007-02-15T05:30:00.0000000+05:30</Value>
              </CollectedStartDT>
            </Specimen>
            <Results>
              <Observation>
                <Identifier>
			<Code>4</Code>
                  <SpecimenType>AMN</SpecimenType>
                </Identifier>
              </Observation>
            </Results>
          </TestRequest>


          <TestRequest CollectionStatus="Resulted">
            <Category>Chem</Category>
            <Specimen>
              <CollectedStartDT>
                <Value>2007-02-15T05:30:00.0000000+05:30</Value>
              </CollectedStartDT>
            </Specimen>            
            <Results>
              <Observation>
                <Identifier>
			<Code>5</Code>
                  <SpecimenType>AMN</SpecimenType>
                </Identifier>
              </Observation>
            </Results>
          </TestRequest>


          <TestRequest CollectionStatus="Resulted">
            <Category>Allergen</Category>
            <Specimen>
              <CollectedStartDT>
                <Value>2007-02-14T05:30:00.0000000+05:30</Value>
              </CollectedStartDT>
            </Specimen>
            <Results>
              <Observation>
                <Identifier>
			<Code>6</Code>
                  <SpecimenType>AMN</SpecimenType>
                </Identifier>
              </Observation>
            </Results>
          </TestRequest>


        </TestRequests>



I am using the following key to group by Category,CollectedStartDate abd 
Specimen Type

<xsl:key name="TestRequestGroupByCategoryCollStDtandSpecimenType" 
match="*[local-name()='InquiryMessage']/*[local-name()='ResultSet']
/*[local-name()='Results']/*[local-name()='Order']/*[local-name()='TestRequests']/*[local-name()='TestRequest']
[@CollectionStatus='Resulted']" 
use="concat(*[local-name()='Category'],' ',
*[local-name()='Specimen']/*[local-name()='CollectedStartDT']/*[local-name()='Value'], ' ',
*[local-name()='Results']/*[local-name()='Observation']/*[local-name()='Identifier']/*[local-name()='SpecimenType'])"/>



<xsl:for-each 
select="*[local-name()='InquiryMessage']/*[local-name()='ResultSet']/*[local-name()='Results']
/*[local-name()='Order']/*[local-name()='TestRequests']/*[local-name()='TestRequest']
[generate-id(.) = 
generate-id(key('TestRequestGroupByCategoryCollStDtandSpecimenType',concat(*[local-name()='Category'], ' ',
*[local-name()='Specimen']/*[local-name()='CollectedStartDT']/*[local-name()='Value'], ' ',
*[local-name()='Results']/*[local-name()='Observation']/*[local-name()='Identifier']/*[local-name()='SpecimenType']))[1])]">


categories are sorted alphabetically
Collection Date/Time sorted descending order


			<xsl:variable name="categName">
				<xsl:value-of select="*[local-name()='Category']"/>
			</xsl:variable>
			<xsl:value-of select="$categName"/>
			
			....
			....
			....

</xsl:for-each>

The output is 

Currently
---------

Allergen
Collection Date/Time: 02/15/2007 00:00:00, Type:  AMN

Allergen
Collection Date/Time: 02/15/2007 00:00:00, Type:  BIFL

Allergen
Collection Date/Time: 02/14/2007 00:00:00, Type:  AMN

Chem
Collection Date/Time: 02/15/2007 00:00:00, Type:  AMN


How to suppess when the category in the grouping repeats to get the 
following output?

Expected
--------

Allergen
Collection Date/Time: 02/15/2007 00:00:00, Type:  AMN


Collection Date/Time: 02/15/2007 00:00:00, Type:  BIFL


Collection Date/Time: 02/14/2007 00:00:00, Type:  AMN

Chem
Collection Date/Time: 02/15/2007 00:00:00, Type:  AMN