CREATE PROCEDURE [dbo].[CheckSomething]
AS
    SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED

    BEGIN TRANSACTION

    -- Do checks

    COMMIT TRANSACTION

CREATE PROCEDURE [dbo].[DoSomethingImportant]
AS
    SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

    BEGIN TRANSACTION

    EXECUTE [dbo].[CheckSomething]

    -- Do some work

    COMMIT TRANSACTION