At what age is it recommended to use PTSD Checklist-Civilian (PCL-C) Questionnaire. Can it be used for screening from the age of 15 or from the age of 18?
I think that the PCL-C or S can be used at least with 16-year-olds and I am pretty sure that it is also fine clinically to extend down to 15 or even younger; but I have not seen a study on this. The measure essentially reiterates the DSM criteria with a severity scale. As long as the clinician is clear that the teenager understands the instructions and language and is precise about the items referring to the trauma specified and within the time-frame specified, it should be clinically valid.
The CPSS is one good possibility as suggested by Steve Janssen. In the US, the more frequently used measure validated for adolescents is the UCLA PTSD Index (based on former UCLA Reaction Index). It is freely accessible. See the following information from the National PTSD Center website:
UCLA PTSD Index for DSM-IV
Description
The UCLA PTSD Index for DSM-IV (UPID) (Pynoos, et al., 1998) is a revision of the Child PTSD Reaction Index: CPTS-RI. It is a 48-item semi-structured interview that assesses a child's exposure to 26 types of traumatic events and assesses DSM-IV PTSD diagnostic criteria. It includes 19 items to assess the 17 symptoms of PTSD as well as 2 associated symptoms (guilt and fear of event's recurring).
Additional Resources
The National Center for Child Traumatic Stress has a power point that can be viewed on administering and scoring the UCLA reaction index (http://www.nctsnet.org*)
References
Pynoos, R., Rodriguez, N., Steinberg, A., Stuber, M., & Frederick, C. (1998). UCLA PTSD Index for DSM-IV.
Steinberg, A., Brymer, M., Decker, K., Pynoos, RS. (2004). The UCLA PTSD Reaction Index. Current Psychiatry Reports 6:96-100.
Steinberg, A., Brymer, M. (2008). The UCLA PTSD Reaction Index. In: G. Reyes, J. Elhai, J. Ford (eds.) Encyclopedia of Psychological Trauma, John Wiley & Sons, Ltd., 673-674.
To Obtain Scale
The University of California requires a licensing agreement for the use of the scale. For assistance, contact:
UCLA PTSD Index for DSM-IV: UCLA Trauma Psychiatry Service
I would concur with Daniel Schechter: I believe you should be fine using the PCL-C with 15-year-olds, at least in clinical use, and provided you know the person and can be confident they understand the questions. For systematic research, however, I would rather recommend one of the scales developed specifically for children and adolescents.