SCROLLINFO si = new SCROLLINFO();
si.cbSize = (uint)Marshal.SizeOf(si);
si.fMask = (uint)ScrollInfoMask.SIF_ALL;
WIN32.GetScrollInfo(this.Handle, (int)SBOrientation.SB_VERT, ref si)

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetScrollInfo(IntPtr hwnd, int fnBar, ref SCROLLINFO lpsi);

[Serializable, StructLayout(LayoutKind.Sequential)]
public class SCROLLINFO
{
    public uint cbSize;
    public uint fMask;
    public int nMin;
    public int nMax;
    public uint nPage;
    public int nPos;
    public int nTrackPos;
}

public enum ScrollInfoMask : uint
{
    SIF_RANGE = 0x1,
    SIF_PAGE = 0x2,
    SIF_POS = 0x4,
    SIF_DISABLENOSCROLL = 0x8,
    SIF_TRACKPOS = 0x10,
    SIF_ALL = (SIF_RANGE | SIF_PAGE | SIF_POS | SIF_TRACKPOS),
}