SQL Query - Select Top or Max

Per my client, they need the last HGBA1C Value (which is the o.OBSVALUE) along with the last date that corresponds with this (o.ObsDate). In my query below, I am getting more then one record for a specific patient. How could I just return the patients one date and value versus them all? SELECT TOP 1 maybe? Not 100% sure.

---- Last HGBA1C Value / Date Last HGBA1C Value / (HGBA1C is obs.HDID = 28)

SELECT  o.pid,
        pp.PatientId,
        pp.PatientProfileId,
        dbo.FormatName('', pp.First, pp.Middle, pp.Last, pp.Suffix) AS PatientName,
        MAX(o.OBSDate) AS obsdate,
        o.OBSVALUE
FROM    OBS AS o
        JOIN OBSHEAD AS oh ON o.HDID = oh.HDID
        JOIN PatientProfile AS pp ON o.PID = pp.PId
WHERE   o.HDID = 28
GROUP BY o.PID,
        pp.PatientId,
        pp.PatientProfileId,
        dbo.FormatName('', pp.First, pp.Middle, pp.Last, pp.Suffix),
        o.OBSVALUE