%macro ck_dups(din=, byvars=usubjid, keepvars=, whrstr=, dout=ck_dups);

    %let lastvar=%scan(&byvars, -1);
	%let din0=%scan(&din, -1);
   
    *** sort data     *****;
    proc sort data=&din out=&din0; by &byvars; &whrstr; run;

    ***** find dups visits   *****;    
    data &dout;
        set &din0;
        by &byvars;

        if first.&lastvar and last.&lastvar then delete;
		%if &keepvars ne  %then %do;
			keep &keepvars;
		%end;
    run;

 %mend ck_dups;


%ck_dups(din=sdtm.lb, byvars=%str(usubjid lbtestcd lbdtc));