Journal of Depression and Anxiety Disorders

ISSN: 2643-5993

Original Study | VOLUME 4 | ISSUE 1 | DOI: 10.36959/362/484 OPEN ACCESS

Post-Traumatic Stress Disorder: Identifying Potential Differences in Participant Response to CAPS-5 Life Events Checklist Questionnaire Based on Gender

Mark W Ruddock, Joanne Watt, Mary Jo Kurth, Cherith N Reid, John V Lamont and Peter Fitzgerald

  • Mark W Ruddock 1*
  • Joanne Watt 1
  • Mary Jo Kurth 1
  • Cherith N Reid 1
  • John V Lamont 1
  • Peter Fitzgerald 1
  • Randox Laboratories Ltd, Clinical Studies Group, Randox Science Park, Northern Ireland, UK

Ruddock MW, Watt J, Kurth MJ, et al. (2022) Post-Traumatic Stress Disorder: Identifying Potential Differences in Participant Response to CAPS-5 Life Events Checklist Questionnaire Based on Gender. J Depress Anxiety Disord 4(1):127-131 Open

Accepted: October 20, 2022 | Published Online: October 22, 2022

Post-Traumatic Stress Disorder: Identifying Potential Differences in Participant Response to CAPS-5 Life Events Checklist Questionnaire Based on Gender

Abstract


Introduction: Post-traumatic stress disorder (PTSD) is a complicated and debilitating psychiatric condition that affects 1 in 3 people who have been exposed to, witnessed, or learned about a traumatic event. Females are almost 2-fold as likely to meet the criteria for PTSD and almost 4-fold as likely than males to develop chronic PTSD. In this pilot study, we examined Life Events Checklist Questionnaire responses from participants who were clinically diagnosed with PTSD to identify if there was a difference in response to checklist questions based on gender.

Materials and methods: Study participants (N = 39; n = 17 (43.6%) males; n = 22 (56.4%) females), with a PTSD diagnosis, were recruited in the US between January and June 2019 by PrecisionMed, California, USA. Study participants were matched for age, gender, and ethnicity. A CAPS-5 Life Events Checklist Questionnaire was applied at interview and symptom severity was calculated based on the sum of the participant responses.

Results: In total, N = 33 questions from the CAPS-5 Life Events Checklist Questionnaire were addressed to each of the study participants. All but one question was significantly different between males and females; namely, the inability to recall certain aspects of the traumatic event (p < 0.05) (chi square χ2). However, as the patient cohort size was limited (N = 39), we applied a post hoc Bonferroni (α = 0.05/33 = 0.0015) to account for any potential bias in the results. Based on the post hoc analysis, we did not observe any differences in the participant response based on gender.

Conclusions: Although the literature identifies gender as a significant risk for PTSD, in this participant cohort, we failed to observe any differences in the subject response to the CAPS-5 Life Events Checklist Questionnaire. The only finding that was significant was that females were 3-times more likely to experience sexual abuse than males. However, it is likely that males are more resistant to report sexual abuse, as was noted in the case report forms.

Keywords


PTSD, Gender, CAPS-5, Screening, Life events checklist

Introduction


Post-traumatic stress disorder (PTSD) is a psychiatric condition that may develop following exposure to, witnessing, or learning about a traumatic event [1]. Pre-existing factors which may contribute to PTSD susceptibility include an underlying genetic predisposition, physical injury and associated pain (i.e., actual or threatened death, serious injury, or sexual violence), hyperreactive physiological responses to stress, gender, sleep disturbances (falling and staying asleep), and structural and functional brain abnormalities [2-5]. Symptoms may include flashbacks, nightmares, severe anxiety, panic attacks, as well as uncontrollable thoughts about the event (intrusive memories) [6].

PTSD can develop immediately, or it can occur weeks, months and sometimes years after the potential traumatic event (PTE). In general, PTSD has been estimated to affect almost 1 in 3 people who have experienced a PTE. However, it is still not clear why some people develop the condition and others do not [7].

Sleep disturbances are a common presentation, occurring in almost 90% of all PTSD patients [8]. Self-medication, and alcohol abuse, contribute to increased insomnia and have significant negative consequences for individuals with pre-existing psychiatric conditions e.g., anxiety and depression, which are common comorbidities that are often associated with PTSD [9].

Fortunately, PTSD can be successfully treated, even when it develops years after the PTE e.g., antidepressants (i.e., paroxetine or sertraline) and/or psychological therapies (i.e., trauma-focused cognitive behavioural therapy (CBT) or movement desensitisation and reprocessing (EDMR)). However, treatment options will depend on the severity of the presenting symptoms and there is not one size fits all when it comes to treatment options [10].

For most people who have been exposed to a PTE, their reactions may include shock, fear, nervousness, anger, and even guilt [11]. These reactions are quite common, and in many people, they will self-resolve. However, in subjects that develop PTSD, these feelings continue and increase, significantly impacting their daily life. For example, subjects that experience PTSD > 1 month do not function as well as before the exposure to the PTE [12].

Gender is an identified risk factor for PTSD [13,14], and as such, females are twice as likely to develop PTSD than males [15]. One reason why females may be more at risk of PTSD, is that females are more likely to experience a sexual assault and/or child sexual abuse [16]. As a result, females are twice as likely to meet the criteria for PTSD and are also four times as likely than males to develop chronic PTSD.

Using the CAPS-5 Case Report Form - PTSD Screening (Life Events Checklist Questionnaire), we investigated the following; exposure type and patient score for: unwanted memories; unpleasant dreams; flashbacks; prolonged psychological distress; physical reactions; avoidance; difficulty remembering; negative beliefs; persistent, distorted cognitions; negative feelings; diminished interest; feeling of detachment; persistent inability to experience positive emotions; irritable behaviour; reckless and self-destructive behaviour; hypervigilance; exaggerated startle response; problems with concentration; sleep disturbances (falling and staying asleep); onset of symptoms; duration of symptoms; subjective distress; impairment in social functioning; impairment in occupational or other important areas of functioning; global validity (patient response); global severity (distress); global improvement (improvement in condition); depersonalization; and derealization; to identify potential differences in PTSD patient response based on gender.

Materials and Methods


Study participants

Study participants were recruited in the USA between January and June 2019 by PrecisionMed, California, USA. Participants were matched for age, gender and ethnicity. Inclusion criteria included a signed and approved written informed consent form, male or female ≥ 18 years of age, and subject is of any ethnic origin. Exclusion criteria included subjects < 18 years of age, evidence of neuropsychiatric disease, subject weighs < 45 kg, and pregnancy. The study conformed to all Data Use Agreements. Participant samples are deidentified and were publicly available and are thus exempt from the requirement of the Institutional Review Board (IRB) approval (Exempt Category 4). A CAPS-5 assessment was undertaken by a clinician and/or psychologist. CAPS-5 scores were available for all N = 39 individuals.

Psychological assessment

The CAPS-5 Life Events Checklist Questionnaire is applied at clinical interviews to assess risk of PTSD and associated psychiatric illness. The CAPS-5 total symptom severity score is then calculated by summing (∑) the response to questions that are put to each of the participants (0 = absent, 1 = mild/subthreshold, 2 = moderate/threshold, 3 = severe/markedly elevated, and 4 = extreme/incapacitating). A score of < 33 is often considered negative for PTSD. For one participant the ∑ was < 33 however, the clinical diagnoses recorded on the patient's notes by the clinician were PTSD. Additional notes and comments made by the subjects at interview were recorded on the CAPS-5 Life Events Checklist Questionnaire and included, but were not limited to, difficulty to forget and avoid memories of the event (flashbacks and unwanted memories, many associated with smell), alertness (loud noises), extreme guilt, disconnection, anxiety, depression, pain, abandonment, not being able to trust their own judgement (or others), helplessness, sad, angry (anger management issues), isolated, frustrated, cautious, suspicious, difficulty falling and staying asleep, and an inability to focus on the positive.

Clinical characteristics

Sociodemographic and clinical characteristics of the PTSD participants involved in the study, including behaviours (smoking (years) and alcohol use (Y/N)), BMI, pulse, blood pressure, comorbidities (including psychological e.g., depression, anxiety, panic disorder, ADD, suicide ideation), medications, substance abuse, and serum biomarker measurements, have been described previously [17].

Statistical analysis

Statistical analysis was performed using SPSS Statistics for Windows, Version 25 (IBM Corp, Armonk, New York). Categorical variables are presented as percentage (%) and were compared using a chi square (χ2) test. A p value < 0.05 was considered significant. A post hoc Bonferroni was applied to minimise potential bias.

Results


Exposure type

Study participants were asked to describe the traumatic event that they considered triggered their PTSD. Subject responses were noted as either (a) Experienced; (b) Witnessed; (c) Learned about; (d) Exposed to adverse details, or combinations thereof. In addition, the PTSD participants were also asked if the trauma exposure type was (i) A threat to life; (ii) A serious physical injury; (iii) Sexual violence, or again, combinations thereof (Table 1).

CAPS-5 life events checklist questionnaire

Each participant in the study answered a CAPS-5 Life Events Checklist Questionnaire, undertaken by a qualified clinician or psychologist. In all cases, the psychiatric diagnosis was PTSD (behaviours, medications, comorbidities and other clinical parameters have been reported previously) [17]. A summary of the CAPS-5 Life Events Checklist questionnaire and results are detailed in Table 2.

CAPS-5 life events checklist questionnaire results

Applying a post hoc Bonferroni, based on the number of questions that were asked of the study participants in the CAPS-5 Life Events Checklist Questionnaire (n = 33), we assigned statistical significant based on the following equation; α = 0.05/33 = 0.0015. Therefore, a significance less than p < 0.0015 was considered significant. As such, it was not unexpected that we did not observe any differences in the CAPS-5 Life Events Checklist Questionnaire response based on gender, for this small participant cohort.

Discussion


Post-traumatic stress disorder is a common psychiatric presentation that is normally associated with exposure to, witnessing, or learning about a traumatic event [18]. However, PTSD can be the result of other events, e.g., the working environment [19]; abusive co-workers [20], critical illness [21], and sexual harassment [22]; as noted in the Life Events Checklist Questionnaire.

PTEs that drive PTSD, or the perception of the trauma event, differ significantly between individuals e.g., one individual that is harassed at work may shrug it off however, another may suffer a psychiatric illness. The reason why one individual develops PTSD and another does not, is the subject of ongoing research [23]. However, individuals that are harbingers of underlying asymptomatic pathologies, such as a psychiatric illness, may be more at risk of PTSD following a PTE.

PTSD affects all socioeconomic demographics and an individual's social status is not guaranteed to be protective, albeit, subjects that have, or maintain a lower socioeconomic status, are more likely to be exposed to trauma events [24]. Therefore, it is unsurprising that this demographic is at higher risk of PTSD.

According to the National Centre for PTSD [25], females are twice as likely to experience PTSD than males (10% (10-12% lifetime prevalence) vs. 4% (5-6% lifetime prevalence), respectively) [26]. Reasons for this disparity suggest that males are more likely to encounter traumas such as physical assault, accidents, and see more death (combat). On the other hand, females are more likely to experience sexual assault and/or sexual abuse as a child [27]. Incidents reported by the National Sexual Violence Resource Centre suggest that 91% of rapes and sexual assault victims are women, and 9% are males [28]. However, this number may be significantly underreported, as many males are more resistant to report the sexual assault to their person. This reluctance to discuss sexual assault, if gender was male, was noted on the Life Events Checklist Questionnaire.

It has been suggested that females that experience PTSD are more likely to exhibit the following symptoms: easily startled (exaggerated startle response), have trouble feeling any emotion, avoid trauma reminders, have intrusive thoughts, are anxious, irritable, and feel numb. However, in direct contrast, males with PTSD are noted to have difficulty controlling their anger and regulating their mood, they constantly brace for further potential trauma, feel helpless, lonely, isolated, and ashamed. Furthermore, males are noted to be more likely to abuse alcohol, smoke more cigarettes, take more medications, and often withdraw from friends and family [15].

In this pilot study, we did not observe any significant differences in the answers to CAPS-5 Life Events Checklist Questionnaire based on gender, albeit, the number of participants involved in the study were only N = 39. However, our observations are aligned with findings reported by Hapke, et al. [29]. In their study, they stated that 'women do not have a higher vulnerability for PTSD'. They concluded that 'sexually-motivated violence and pre-existing anxiety disorders were the main reason for higher prevalence's of PTSD.'

One of the limitations of our study was that we were unaware if the participants involved had pre-existing psychiatric conditions prior to their PTSD diagnosis. Albeit, the participant report forms would suggest that several individuals sought help because of underlying health conditions, including psychiatric conditions, such as anxiety and depression. For all individuals who were diagnosed with PTSD, anxiety and/or depression was comorbid. Furthermore, physical and psychological comorbidities were recorded for all subjects, namely pain and sleep disturbances. These finding have been reported earlier [17].

However, the question remains that if the underlying comorbidities are significant contributors to risk, irrespective of gender, as suggested by Hapke, et al. [29] for a PTSD diagnosis, after a PTE, or if they are precipitated by the PTSD. This will be the subject of further investigation in a larger patient cohort.

References


  1. Alexander KS, Nalloor R, Bunting KM, et al. (2020) Investigating individual pre-trauma susceptibility to a PTSD-Like phenotype in animals. Front Syst Neurosci 13: 85.
  2. Christiansen DM, Elklit A (2008) Risk factors predict post-traumatic stress disorder differently in men and women. Ann Gen Psychiatry 7: 24.
  3. Brewin CR, Andrews B, Valentine JD (2000) Meta-analysis of risk factors for posttraumatic stress disorder in trauma-exposed adults. J Consult Clin Psychol 68: 748-766.
  4. Maguire DG, Ruddock MW, Milanak ME, et al. (2020) Sleep, a governor of morbidity in PTSD: A systematic review of biological markers in PTSD-related sleep disturbances. Nat Sci Sleep 12: 545-562.
  5. Lee H, Lee K, Jeon J, et al. (2019) 0060 Hippocampal response to sleep-related pictures moderates the association between sleep disturbance and impulsivity. Sleep 42: A25-A25.
  6. Bisson JI, Cosgrove S, Lewis C, et al. (2015) Post-traumatic stress disorder. BMJ 26: 351: h6161.
  7. Christensen RC (2012) The development of posttraumatic stress disorder following an unusual life event: A case report. Innov Clin Neurosci 9: 26-28.
  8. Pace-Schott EF, Germain A, Milad MR (2015) Sleep and REM sleep disturbance in the pathophysiology of PTSD: The role of extinction memory. Biol Mood Anxiety Disord 5: 3.
  9. Leeies M, Pagura J, Sareen J, et al. (2010) The use of alcohol and drugs to self-medicate symptoms of posttraumatic stress disorder. Depress Anxiety 27: 731-736.
  10. Zoellner LA, Feeny NC, Cochran B, et al. (2003) Treatment choice for PTSD. Behav Res Ther 41: 879-886.
  11. Lee DA, Scragg P, Turner S (2001) The role of shame and guilt in traumatic events: A clinical model of shame-based and guilt-based PTSD. Br J Med Psychol 74: 451-466.
  12. Clifton EG, Feeny NC, Zoellner LA (2017) Anger and guilt in treatment for chronic posttraumatic stress disorder. J Behav Ther Exp Psychiatry 54: 9-16.
  13. Norris FH, Foster JD, Weisshaar DL (2002) The epidemiology of gender differences in PTSD across developmental, societal, and research contexts. In: R Kimerling, P Ouimette, J Wolfe, Gender PTSD. The Guilford Press, 3-42.
  14. Tolin DF, Foa EB (2002) Gender and PTSD: A cognitive model. In: R Kimerling, P Ouimette, J Wolfe, Gender PTSD. The Guilford Press, 76-97.
  15. Olff M (2017) Sex and gender differences in post-traumatic stress disorder: An update. Eur J Psychotraumatol 8: 1351204.
  16. How Common is PTSD in Women? PTSD: National Center for PTSD. (https://www.ptsd.va.gov/understand/common/common_women.asp)
  17. Maguire D, Watt J, Armour C, et al. (2021) Post-traumatic stress disorder: A biopsychosocial case-control study investigating peripheral blood protein biomarkers. Biomarkers in Neuropsychiatry 5: 100042.
  18. Perrin M, Vandeleur CL, Castelao E, et al. (2013) Determinants of the development of post-traumatic stress disorder, in the general population. Soc Psychiatry Psychiatr Epidemiol 49: 447-457.
  19. PTSD At Work - UK Charity - Supporting the UK workforce.
  20. The Trauma of Workplace Bullying. (https://psychcentral.com/pro/recovery-expert/2017/07/the-trauma-of-workplace-bullying#1)
  21. Hatch R, Young D, Barber V, et al. (2018) Anxiety, Depression and Post Traumatic Stress Disorder after critical illness: A UK-wide prospective cohort study. Crit Care 22: 310.
  22. Chivers-Wilson KA (2006) Sexual assault and posttraumatic stress disorder: A review of the biological, psychological and sociological factors and treatments. McGill J Med MJM 9: 111-118.
  23. Dopfel D, Perez PD, Verbitsky A, et al. (2019) Individual variability in behavior and functional networks predicts vulnerability using an animal model of PTSD. Nat Commun 10: 2372.
  24. Parto JA, Evans MK, Zonderman AB (2011) Symptoms of posttraumatic stress disorder among urban residents. J Nerv Ment Dis 199: 436-439.
  25. PTSD: National Center for PTSD Home. (https://www.ptsd.va.gov/)
  26. Post-Traumatic Stress Disorder in Women: Signs & Symptoms - Capital Women's Care | MD, DC, & VA. (https://www.cwcare.net/news/post-traumatic-stress-disorder-women-signs-symptoms)
  27. Seng JS, Low LK, Sperlich M, et al. (2011) Post-traumatic stress disorder, child abuse history, birthweight and gestational age: A prospective cohort study. BJOG 118: 1329-1339.
  28. National Sexual Violence Resource Center (NSVRC). (https://www.nsvrc.org/)
  29. Hapke U, Schumann A, Rumpf HJ, et al. (2006) Post-traumatic stress disorder: The role of trauma, pre-existing psychiatric disorders, and gender. Eur Arch Psychiatry Clin Neurosci 256: 299-306.

Introduction: Post-traumatic stress disorder (PTSD) is a complicated and debilitating psychiatric condition that affects 1 in 3 people who have been exposed to, witnessed, or learned about a traumatic event. Females are almost 2-fold as likely to meet the criteria for PTSD and almost 4-fold as likely than males to develop chronic PTSD. In this pilot study, we examined Life Events Checklist Questionnaire responses from participants who were clinically diagnosed with PTSD to identify if there was a difference in response to checklist questions based on gender.

Materials and methods: Study participants (N = 39; n = 17 (43.6%) males; n = 22 (56.4%) females), with a PTSD diagnosis, were recruited in the US between January and June 2019 by PrecisionMed, California, USA. Study participants were matched for age, gender, and ethnicity. A CAPS-5 Life Events Checklist Questionnaire was applied at interview and symptom severity was calculated based on the sum of the participant responses.

Results: In total, N = 33 questions from the CAPS-5 Life Events Checklist Questionnaire were addressed to each of the study participants. All but one question was significantly different between males and females; namely, the inability to recall certain aspects of the traumatic event (p < 0.05) (chi square χ2). However, as the patient cohort size was limited (N = 39), we applied a post hoc Bonferroni (α = 0.05/33 = 0.0015) to account for any potential bias in the results. Based on the post hoc analysis, we did not observe any differences in the participant response based on gender.

Conclusions: Although the literature identifies gender as a significant risk for PTSD, in this participant cohort, we failed to observe any differences in the subject response to the CAPS-5 Life Events Checklist Questionnaire. The only finding that was significant was that females were 3-times more likely to experience sexual abuse than males. However, it is likely that males are more resistant to report sexual abuse, as was noted in the case report forms.

References

  1. Alexander KS, Nalloor R, Bunting KM, et al. (2020) Investigating individual pre-trauma susceptibility to a PTSD-Like phenotype in animals. Front Syst Neurosci 13: 85.
  2. Christiansen DM, Elklit A (2008) Risk factors predict post-traumatic stress disorder differently in men and women. Ann Gen Psychiatry 7: 24.
  3. Brewin CR, Andrews B, Valentine JD (2000) Meta-analysis of risk factors for posttraumatic stress disorder in trauma-exposed adults. J Consult Clin Psychol 68: 748-766.
  4. Maguire DG, Ruddock MW, Milanak ME, et al. (2020) Sleep, a governor of morbidity in PTSD: A systematic review of biological markers in PTSD-related sleep disturbances. Nat Sci Sleep 12: 545-562.
  5. Lee H, Lee K, Jeon J, et al. (2019) 0060 Hippocampal response to sleep-related pictures moderates the association between sleep disturbance and impulsivity. Sleep 42: A25-A25.
  6. Bisson JI, Cosgrove S, Lewis C, et al. (2015) Post-traumatic stress disorder. BMJ 26: 351: h6161.
  7. Christensen RC (2012) The development of posttraumatic stress disorder following an unusual life event: A case report. Innov Clin Neurosci 9: 26-28.
  8. Pace-Schott EF, Germain A, Milad MR (2015) Sleep and REM sleep disturbance in the pathophysiology of PTSD: The role of extinction memory. Biol Mood Anxiety Disord 5: 3.
  9. Leeies M, Pagura J, Sareen J, et al. (2010) The use of alcohol and drugs to self-medicate symptoms of posttraumatic stress disorder. Depress Anxiety 27: 731-736.
  10. Zoellner LA, Feeny NC, Cochran B, et al. (2003) Treatment choice for PTSD. Behav Res Ther 41: 879-886.
  11. Lee DA, Scragg P, Turner S (2001) The role of shame and guilt in traumatic events: A clinical model of shame-based and guilt-based PTSD. Br J Med Psychol 74: 451-466.
  12. Clifton EG, Feeny NC, Zoellner LA (2017) Anger and guilt in treatment for chronic posttraumatic stress disorder. J Behav Ther Exp Psychiatry 54: 9-16.
  13. Norris FH, Foster JD, Weisshaar DL (2002) The epidemiology of gender differences in PTSD across developmental, societal, and research contexts. In: R Kimerling, P Ouimette, J Wolfe, Gender PTSD. The Guilford Press, 3-42.
  14. Tolin DF, Foa EB (2002) Gender and PTSD: A cognitive model. In: R Kimerling, P Ouimette, J Wolfe, Gender PTSD. The Guilford Press, 76-97.
  15. Olff M (2017) Sex and gender differences in post-traumatic stress disorder: An update. Eur J Psychotraumatol 8: 1351204.
  16. How Common is PTSD in Women? PTSD: National Center for PTSD. (https://www.ptsd.va.gov/understand/common/common_women.asp)
  17. Maguire D, Watt J, Armour C, et al. (2021) Post-traumatic stress disorder: A biopsychosocial case-control study investigating peripheral blood protein biomarkers. Biomarkers in Neuropsychiatry 5: 100042.
  18. Perrin M, Vandeleur CL, Castelao E, et al. (2013) Determinants of the development of post-traumatic stress disorder, in the general population. Soc Psychiatry Psychiatr Epidemiol 49: 447-457.
  19. PTSD At Work - UK Charity - Supporting the UK workforce.
  20. The Trauma of Workplace Bullying. (https://psychcentral.com/pro/recovery-expert/2017/07/the-trauma-of-workplace-bullying#1)
  21. Hatch R, Young D, Barber V, et al. (2018) Anxiety, Depression and Post Traumatic Stress Disorder after critical illness: A UK-wide prospective cohort study. Crit Care 22: 310.
  22. Chivers-Wilson KA (2006) Sexual assault and posttraumatic stress disorder: A review of the biological, psychological and sociological factors and treatments. McGill J Med MJM 9: 111-118.
  23. Dopfel D, Perez PD, Verbitsky A, et al. (2019) Individual variability in behavior and functional networks predicts vulnerability using an animal model of PTSD. Nat Commun 10: 2372.
  24. Parto JA, Evans MK, Zonderman AB (2011) Symptoms of posttraumatic stress disorder among urban residents. J Nerv Ment Dis 199: 436-439.
  25. PTSD: National Center for PTSD Home. (https://www.ptsd.va.gov/)
  26. Post-Traumatic Stress Disorder in Women: Signs & Symptoms - Capital Women's Care | MD, DC, & VA. (https://www.cwcare.net/news/post-traumatic-stress-disorder-women-signs-symptoms)
  27. Seng JS, Low LK, Sperlich M, et al. (2011) Post-traumatic stress disorder, child abuse history, birthweight and gestational age: A prospective cohort study. BJOG 118: 1329-1339.
  28. National Sexual Violence Resource Center (NSVRC). (https://www.nsvrc.org/)
  29. Hapke U, Schumann A, Rumpf HJ, et al. (2006) Post-traumatic stress disorder: The role of trauma, pre-existing psychiatric disorders, and gender. Eur Arch Psychiatry Clin Neurosci 256: 299-306.