CASE
        WHEN @HIV1 = 'Non-reactive' AND @HIV2 = 'Non-reactive' AND @HIV3 = 'Non-reactive' THEN 'Negative'
        WHEN @HIV1 = 'Reactive' AND @HIV2 = 'Reactive' AND @HIV3 = 'Reactive' THEN 'Positive'
        WHEN (@HIV1 = 'Reactive' OR @HIV2 = 'Reactive' OR @HIV3 = 'Reactive') AND
             (@HIV1 = 'Non-reactive' OR @HIV2 = 'Non-reactive' OR @HIV3 = 'Non-reactive' OR
             @HIV1 IS NULL OR @HIV2 IS NULL OR @HIV3 IS NULL)
        THEN 'Inconclusive'
        ELSE 'Unknown'
    END