Do you do assessments in a forensic setting? In other words, had this person committed a crime? BPD and ASPD, that's some scary combo!
I got the advantage of having a great psychologist work with me and the hospital being a host to a psychology master's program where we can have the master's students do plenty of testing. I didn't use testing on this guy because his acting out was so extreme he was not appropriate for testing until yesterday.
The trick with this guy IMHO was that Clonidine greatly stabilized him and he had a few hours of no problems. There were no psychotic symptoms that were clearly psychosis (e.g. no negative symptoms, no delusions, no paranoia), he often acted out if he did not get immediate gratification, and he said antipsychotics made him feel more hyper and they did not sedate him.
Then I found out his mother drank like a fish when she was pregnant. He does show some FAS facial characterstics but that is too nonspecific a test.
What helped me was hours of observation, experience and when we gave an emergency medication, only giving one so we knew exactly what each medication we gave did to him. It came to a head about 3 days ago. I gave him Thorazine 100 mg oral, then 20 minutes later, Prolixin 15 mg oral and crushed, then 25 minutes later Thorazine 100 IM, then put him in restraints. I will not give him Haldol because there is a medical record showing he had seizure a few years ago after he got injected with it. Each time we gave him an antipsychotic he said it just made him feel more hyper. I felt that giving him more was just being a fly hitting the window. I tried Clonidine after he was released from restraints and he told me that for the first time in years he actually felt a medication causing him some improvement. Given that it treats ADHD, he had symptoms of ADHD and that it's not a substance of abuse, I figured this was ADHD of the worst extreme I ever saw.
Another advantage is I work in a long-term facility. In that setting you can devote several hours on one patient a day. In a short term facility, you have to get them out as soon as possible or the institution starts losing money.
It took me about 6 days to figure this out, and another few days to reinforce my theory. Of course nothing is ever 100% but it's to the point where he said he feels better and I'm not giving him anything that can be used for abuse. He's gone through years of being diagnosed with bipolar disorder and being given an antipsychotic and mood stabilizer that did nothing or made him worse. Right now I got him on a starting dose of Wellbutrin and a Clonidine patch and he's been fine for a few days.
I am though doubting he has antisocial PD because since he's been stabilized, he's told me he's regretted some of his prior behaviors. He also calls a family member regularly and cries over the phone because that's his only relative and that person is not in good health. IMHO this is FAS and ADHD to the worst extreme I've seen it--to the point where the guy cannot control impulses to cause a ruckus and he had an urge to cause one moment to moment. Now that he's been a bit more stable, he told me he has an urge to stir things up and the Clonidine's calmed it down. He's not been charged before the incident for which I'm seeing him now, but he has done several misdemeanor level behaviors that could've gotten him arrested but he got away with it. (E.g. screaming in a public place, baiting people into fights in public, etc).