Platelet growth factors from allogeneic platelet-rich plasma for clinical improvement in split-thickness skin graft

Efficacy and safety of platelet-rich plasma as an adjunct therapy to split thickness skin graft in burn patients with granulating raw wounds: a prospective, randomized, double-blind study-study protocol

BACKGROUND

Burn wounds are commonly encountered in clinical settings and the management aims at the prevention of mortality and morbidity due to disability. The platelet-rich plasma (PRP) is blood-derived biomaterial that is enriched with growth factors and cytokines that facilitate wound healing. The PRP has proven its efficacy in various other wounds, but its role in post-burn raw areas and graft take has not been validated. This proposed multicentre randomized controlled trial aims to evaluate the efficacy and safety of platelet-rich plasma as an adjunct therapy to split-thickness skin graft in burn patients with granulating raw wounds.

METHOD/DESIGN

This trial is an investigator-initiated, double-blind multicentre, randomized controlled parallel arm trial alongside trial cost-effectiveness analysis. Granulating deep second-degree and third-degree burns affecting 3-20% of total body surface area (TBSA) at 10-14th post-burn day will be included in the study. A total of 550 patients (275 in each group) will be randomized to receive either standard skin graft or allogenic PRP with skin graft treatment. The primary endpoint will be the mean percentage of graft-take on the 14th postoperative day. The result will be analyzed by two independent assessors who are blinded to the study. Secondary endpoints include (a) time taken for complete wound healing; (b) frequency of adverse events; (c) follow-up with scar index at 3 months, 6 months, and 1 year using the Patient and Observer Scar Assessment Scale (POSAS) score; (d) cost-effectiveness analysis of the intervention compared to the comparator; and (e) to estimate in a subset of participants the association between growth factor levels (PDGF BB and TGF ß-1) of activated PRP and clinical response.

DISCUSSION

The proposed trial will be expected to verify the efficacy and safety of PRP for split-thickness skin graft (STSG) in deep second-degree or third-degree granulating wounds of burn patients based on the outcome of the study.

Platelet-rich plasma and plasma rich in growth factors in extra-oral wound care

This narrative review evaluates the existing literature on the clinical efficacy and safety of platelet-rich plasma (PRP) and plasma rich in growth factors (PRGFs) in extra-oral wound care, considering their potential benefits and drawbacks. The review specifically focuses on the impact of these treatments on patients' quality of life, pain management, treatment costs, recurrence rates, and potential complications. Given the extensive literature and diverse range of extra-oral wound types in which these autologous platelet concentrates have been applied, this narrative review focuses on the most frequently described wound types, including diabetic foot ulcers, venous leg ulcers, pressure ulcers, surgical wounds, and burns. The use of PRP has been reported in various medical specialties, with a low risk of adverse events. While there is a growing interest in the use of PRGF with promising results, the available literature on this topic is still limited. Only a few studies evaluated patients' perception of the treatment and the relationship between treatment costs and clinical outcomes. Data on recurrence rates and complications also vary across studies. In conclusion, PRP and PRGF show promise as alternatives or as adjunctive therapies to conventional treatments for various extra-oral wounds and ulcers, leading to reduced wound size and accelerated healing time but should be considered on a case-by-case basis, taking into account the type and severity of the wound.

Skin Telocytes Could Fundament the Cellular Mechanisms of Wound Healing in Platelet-Rich Plasma Administration

For more than 40 years, autologous platelet concentrates have been used in clinical medicine. Since the first formula used, namely platelet-rich plasma (PRP), other platelet concentrates have been experimented with, including platelet-rich fibrin and concentrated growth factor. Platelet concentrates have three standard characteristics: they act as scaffolds, they serve as a source of growth factors and cytokines, and they contain live cells. PRP has become extensively used in regenerative medicine for the successful treatment of a variety of clinical (non-)dermatological conditions like alopecies, acne scars, skin burns, skin ulcers, muscle, cartilage, and bone repair, and as an adjuvant in post-surgery wound healing, with obvious benefits in terms of functionality and aesthetic recovery of affected tissues/organs. These indications were well documented, and a large amount of evidence has already been published supporting the efficacy of this method. The primordial principle behind minimally invasive PRP treatments is the usage of the patient's own platelets. The benefits of the autologous transplantation of thrombocytes are significant, representing a fast and economic method that requires only basic equipment and training, and it is biocompatible, thus being a low risk for the patient (infection and immunological reactions can be virtually disregarded). Usually, the structural benefits of applying PRP are attributed to fibroblasts only, as they are considered the most numerous cell population within the interstitium. However, this apparent simplistic explanation is still eluding those different types of interstitial cells (distinct from fibroblasts) that are residing within stromal tissue, e.g., telocytes (TCs). Moreover, dermal TCs have an already documented potential in angiogenesis (extra-cutaneous, but also within skin), and their implication in skin recovery in a few dermatological conditions was attested and described ultrastructurally and immunophenotypically. Interestingly, PRP biochemically consists of a series of growth factors, cytokines, and other molecules, to which TCs have also proven to have a positive expression. Thus, it is attractive to hypothesize and to document any tissular collaboration between cutaneous administered PRP and local dermal TCs in skin recovery/repair/regeneration. Therefore, TCs could be perceived as the missing link necessary to provide a solid explanation of the good results achieved by administering PRP in skin-repairing processes.

Prevention and Management of Complications in Nasal Reconstruction

Nasal reconstruction is a challenging practice with the potential for complications. Surgeons can prevent complications through preoperative optimization of patient factors, refinement of intraoperative surgical techniques, and postoperative surgical and nonsurgical wound care. Preoperatively, optimization of modifiable and recognition of nonmodifiable risk factors is paramount. Intraoperatively, meticulous flap design and surgical technique promote healing. In the postoperative setting, attentive wound care, adjuvant therapies, and close follow-up for consideration of additional procedures enhance outcomes. By anticipating potential complications across perioperative settings, surgeons can prevent common complications in nasal reconstruction and more effectively manage those complications that arise.

[Clinical efficacy of local injection of platelet-rich plasma combined with double-layer artificial dermis in treating wounds with exposed tendon on extremity]

Objective: To investigate the clinical efficacy of local injection of platelet-rich plasma (PRP) combined with double-layer artificial dermis in treating wounds with exposed tendon on extremity. Methods: A retrospective observational study was conducted. From December 2017 to October 2022, 16 patients were admitted to Department of Orthopaedic Trauma of the Second Affiliated Hospital of Guizhou University of Traditional Chinese Medicine, and 32 patients were admitted to Department of Burns and Plastic Surgery of Guiyang Steel Factory Staff Hospital. All the patients had wounds with exposed tendon on extremity caused by various reasons and met the inclusion criteria. There were 39 males and 9 females, aged 26 to 58 years. The patients were divided into PRP alone group, artificial dermis alone group, and PRP+artificial dermis group, with 16 patients in each group. The wounds were treated with autologous PRP, double-layer artificial dermis, or thei combination of autologous PRP and double-layer artificial dermis, followed by autologous split-thickness scalp grafting after good growth of granulation tissue. On the 7th day after the secondary surgery, the autograft survival was observed, and the survival rate was calculated. The wound healing time and length of hospital stay of patients were recorded. At 3 and 6 months after wound healing, the Vancouver scar scale (VSS) was used to score the pigmentation, height, vascularity, and pliability of scars, and the total score was calculated. Adverse reactions during the entire treatment process were recorded. Data were statistically analyzed with chi-square test, Fisher's exact probability test, one-way analysis of variance, least significant difference test, Kruskal-Wallis H test, Nemenyi test, and Bonferroni correction. Results: On the 7th day after the secondary surgery, there was no statistically significant difference in the autograft survival rate of patients among PRP alone group, artificial dermis alone group, and PRP+artificial dermis group (P>0.05). The wound healing time and length of hospital stay of patients in PRP+artificial dermis group were (20.1±3.0) and (24±4) d, respectively, which were significantly shorter than (24.4±5.5) and (30±8) d in PRP alone group (P<0.05) and (24.8±4.9) and (32±8) d in artificial dermis alone group (P<0.05). At 3 and 6 months after wound healing, the pliability scores of patients in PRP+artificial dermis group were significantly lower than those in PRP alone group (with Z values of 12.91 and 15.69, respectively, P<0.05) and artificial dermis alone group (with Z values of 12.50 and 12.91, respectively, P<0.05). There were no statistically significant differences in pigmentation, vascularity, height scores, and total score of scar of patients among the three groups (P>0.05). In artificial dermis alone group, one patient experienced partial liquefaction and detachment of the double-layer artificial dermis due to local infection of Staphylococcus epidermidis, which received wound dressing change, second artificial dermis transplantation, and subsequent treatment as before. No adverse reactions occurred in the remaining patients during the whole treatment process. Conclusions: Local injection of PRP combined with double-layer artificial dermis is effective in treating wounds with exposed tendon on extremity, which can not only significantly shorten wound healing time and length of hospital stay, but also improve scar pliability after wound healing to some extent in the long term. It is a clinically valuable treatment technique that is worth promoting and applying.

Role for platelet rich plasma as an adjuvant therapy in wound healing and burns

Background

Platelet rich plasma (PRP) contains high concentrations of growth factors. Intuitively, these were thought to be of potential benefit in healing of chronic wounds, skin grafts and graft donor sites. This was echoed in retrospective studies and an individual case basis but had not been randomized.

Methods

A systematic search was carried out by two individuals, independently, on the MEDLINE, EMBASE and COCHRANE databases, according to PRISMA guidelines. All data analysis and statistics was pooled and analysed using the Cochrane RevMan Software.

Results

Split thickness grafts have been described by numerous authors, but PRP use did not offer a significant advantage in graft take in pooled results (MD 5.83, 95% CI − 0.69 to 12.25, random-effects, p = 0.08). The analysis of included randomized controlled trials has shown favourable split-thickness skin graft donor site healing in the PRP group (MD − 5.55, 95% CI − 7.40 to − 3.69, random-effects, p =  < 0.00001) compared to the control group. For carpal tunnel syndrome, the pooled results showed no difference in functional scores vs steroid injections (SMD − 0.68, 95% CI − 1.47 to 0.10, randomeffects, p = 0.09) or indeed splinting groups.

Conclusions

With the current body of evidence, we conclude that the use of PRP as an adjuvant therapy in skin grafts, burns, carpal tunnel surgery or scars cannot be rationalised. A potential use of PRP is in donor site management but the cost of this would be difficult to justify.

Level of evidence: Not ratable.

Allogeneic platelet-derived growth factors local injection in treatment of tennis elbow: a prospective randomized controlled study

PURPOSE

The purpose of this study aimed to evaluate the efficacy of local injection of allogeneic platelet-derived growth factors in treatment of patients with tennis elbow.

PATIENTS AND METHODS

This study included 120 tennis elbow patients randomly divided into two groups. The patients were locally injected with allogeneic growth factors (treatment group) or with normal saline (control group). The outcomes were assessed using Patient-Related Tennis Elbow Evaluation (PRTEE) and quick Disabilities of the Arm, Shoulder and Hand (qDASH) scales. The clinical outcomes were accordingly classified as excellent, good and poor. The patient's satisfaction and adverse effects were also recorded.

RESULTS

There was no statistically significant difference between the two groups regarding the age, gender, dominant arm or the pre-injection scores. At three month follow-up, the reductions in the mean PRTEE and qDASH scores were 88.7% and 70.6% in the treatment group versus 21.8% and 14.9% in the control group, respectively. At the last follow-up, the outcomes in the treatment group were excellent in 85% of patients and good in 15%, versus 8% and 32% in the control group. Overall, 95% were satisfied in the treatment group compared to 25% in control group. Forty patients in the treatment group experienced mild transient post-injection pain.

CONCLUSION

This study strongly suggests that local injection of allogeneic platelet-derived growth factors could be a promising safe treatment option for tennis elbow with significant pain relief, functional improvement and patient's satisfaction. Yet, additional larger studies are needed to assess the durability of these outcomes.

A platelet-derived hydrogel improves neovascularisation in full thickness wounds

Platelets are a reservoir of growth factors, cytokines and chemokines involved in spontaneous wound repair. In this study, a platelet-rich and fibrin-rich hydrogel was generated from expired platelet components that would have otherwise been transfused. The material contained physiological concentrations of transforming growth factor β1 (TGF-β1, platelet-derived growth factor AB (PDGF-AB), PDGF-BB, insulin-like growth factor-1 (IGF-1), fibroblast growth factor 2 (FGF-2), and epidermal growth factor (EGF). The effect of the hydrogel on wound repair was investigated in SKH-1 mice. Full thickness dorsal wounds were created on the mice and treated with the hydrogel at various concentrations. Immunohistochemical staining with CD31 (endothelial cell marker) revealed that wounds treated with the hydrogel showed significantly enhanced vascularisation in the wound bed. Moreover, high levels of interleukin-6 (IL-6) and KC (IL-8 functional homologue) in treated wounds were sustained over a longer period of time, compared to untreated wounds. We postulate that sustained IL-6 is a driver, at least partly, of enhanced vascularisation in full thickness wounds treated with the hydrogel. Future work is needed to explore whether this hydrogel can be utilised as a treatment option when vascularisation is a critical limitation. STATEMENT OF SIGNIFICANCE: The economic cost of wound repair is estimated in billions of dollars each year. In many cases time required to vascularise wounds is a major contributor to slow wound repair. In this study, we developed a blood-derived platelet- and fibrin-rich hydrogel. It contains a number of growth factors actively involved in spontaneous wound healing. This hydrogel significantly improved dermal repair and vascularisation in a full-thickness wound mouse model. This study provides an action mechanism for modulation of localised inflammation.

Efficacy of Platelet-Rich Plasma in Reduction of Post-Operative Split-Thickness Skin Graft Loss and Hematoma Formation: A Meta-Analysis

Split-thickness skin grafting is a very popular technique of wound closure, especially for large wounds. The success rate of a split-thickness skin graft (STSG) has consistently been in the range of 70-90%. Multiple techniques have been introduced to further improve graft survival, for example, the use of autologous platelet-rich plasma (PRP), thrombin gel, platelet-rich fibrin matrix, and negative pressure wound therapy. We evaluated the impact of PRP use on the survival of STSG through a meta-analysis. We conducted the analysis in accordance with Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) protocol and performed a literature search using the following databases: PubMed, Cochrane, and ClinicalTrials.gov. A total of 126 articles were yielded by the search, out of which four randomized controlled trials (RCTs) were included according to our eligibility criteria and irrelevant articles were excluded. The intervention group received PRP application to the wound bed before applying the graft while the control group received treatment with conventional fixation procedures (sutures and staples). We estimated the pooled odds ratio with a 95% confidence interval (CI). The total number of participants in the analysis was 460. The participants had wounds of varying etiology. Post-operative graft loss and hematoma formation were taken to be the primary and secondary outcome measures, respectively. Thirty-four participants suffered graft loss of differing extent in the control group while three participants suffered graft loss in the intervention group. The pooled odds ratio for graft loss was 0.15 (95% CI: 0.05-0.49; I²=38%; p=0.184) signifying that PRP use decreased the odds of graft loss by 85%. For our secondary outcome measure, 440 participants were studied. Forty-four participants suffered hematoma formation in the control group versus 11 in the intervention group. The pooled odds ratio for hematoma formation was calculated as 0.21 (95% CI: 0.09-0.50; I²=0%; p=0.869) signifying that PRP use decreased the odds of hematoma formation by 79%. PRP appears to significantly impact graft survival, and further studies are needed to strengthen the evidence base for its use in split-thickness skin grafting.

[Not Available]

Platelet rich plasma (PRP) has trophic functions due to a high concentration of growth factors and cytokines. These properties may be of therapeutic interest in the management of burn injuries. In preparation for a clinical study at the Lyon Burn Centre on PRP as an inducer of healing in burns, we carried out a review of the literature looking at the results of the use of this therapy. A review of the literature on the use of PRP for the treatment of burn injuries was performed by querying the PUBMED database using the keywords [platelet rich plasma] AND [burns]. Controlled clinical or pre-clinical studies in English or French were included. Eleven articles were identified, consisting of eight preclinical animal model studies and three clinical studies. These looked at the effects of PRP on the healing of burned areas whether they were grafted or not, on the improvement of neuropathic pain, and on distant skin trophicity. The results of recent preclinical studies show shorter epithelialization times thanks to PRP. In humans, a significant study (201 patients) validates its use in combination with thin skin grafts, and another shows benefits on distant cutaneous trophicity. In conclusion, the use of PRP topically or by injection under the skin has a potential benefit in the management of acute burns. A large-scale series validates its use in clinical practice.

The Adjunct Use of Platelet-Rich Plasma in Split-Thickness Skin Grafts: A Systematic Review

OBJECTIVE

To summarize the available literature on platelet-rich plasma (PRP) as an adjunct to split-thickness skin graft (STSG) in an organized and easy-to-read format. These data may encourage surgeons to integrate PRP into their skin graft protocol.

DATA SOURCES

The authors conducted a systematic search using the PubMed, Cochrane, and ClinicalTrials.gov databases for articles published from their respective inceptions to October 1, 2019, to identify relevant studies.

STUDY SELECTION

A total of 629 articles were reviewed, and 5 were identified for inclusion in this study. The population of all studies was patients receiving an STSG to close a skin defect.

DATA EXTRACTION

Articles were screened for the following outcome measures: graft take rates, edema or hematoma formation, instant adhesion of graft, healing time, length of hospital stay, scar hypertrophy, and frequency of dressing changes.

DATA SYNTHESIS

The data were organized into two tables describing the studies and the selected outcome measures.

CONCLUSIONS

The data suggest that PRP in STSG reduces healing time, length of hospital stay, and scarring and that it eliminates the need for sutures/staples. Further, these benefits may correlate with a decrease in overall expenditure. This systematic review suggests that further research on PRP and skin grafts is warranted.

Prospective Randomized Evaluation of Local Injection of Allogeneic Growth Factors in Plantar Fasciitis

BACKGROUND

The aim of this study was to evaluate the efficacy and safety of injection of allogeneic growth factors in patients with plantar fasciitis.

METHODS

This study included 150 patients who were randomly divided into 2 equal groups; the patients were locally injected with allogeneic growth factors (GFs) (treatment group) or with saline 0.9% (control group). The patients were assessed using visual analog scale (VAS) and Foot Function Index-Revised short form (FFI-Rs) scores preinjection and 1, 3, 6, and 12 months postinjection. The patients were questioned about their satisfaction. Any adverse effects were recorded.

RESULTS

At baseline, there was no significant difference between both groups regarding the mean VAS and FFI-Rs scores. At 3-month follow-up, the reduction in mean VAS score was 87% in the treatment group and 55% in the control group (P < .001), and the reduction in mean FFI-Rs score was 62% in the treatment group and 40% in the control group (P < .001). Treatment group and study visit were significant factors affecting both VAS and FFI-Rs scores. Overall, 92% were satisfied in the treatment group, and 78.2% in the control group. Postinjection pain occurred in 5 patients in the treatment group.

CONCLUSION

This study provides Level I evidence regarding the efficacy and safety of allogeneic GF injection in patients with plantar fasciitis. However, additional studies are needed to evaluate their adverse effects, immunogenicity, and microbiological safety.

LEVEL OF EVIDENCE

Level I, prospective randomized controlled case series.

The application of platelet-rich plasma for skin graft enrichment: A meta-analysis

Existing evidence demonstrated that the role of platelet-rich plasma (PRP) in skin graft enrichment is uncertain. The aim of this study was to evaluate the efficacy and safety of PRP for skin graft. PubMed, EMBASE, Web of Science, and Cochrane Library databases were searched for randomised controlled trials that compared outcomes of skin graft treated with PRP versus those treated with blank controls. The outcomes mainly included the rate of skin graft take, number of skin graft loss and haematoma formation, and complications. There were 11 studies involving a total of 910 cases of skin grafts. Compared with the control group, PRP group had a significantly higher rate of skin graft take (mean difference = 5.47%; 95% confidence interval [CI], 2.80%-8.14%; P < .0001), fewer number of skin graft loss (risk ratio [RR] = 0.26; 95% CI, 0.13-0.55; P = .0004) and fewer cases of haematoma formation (RR = 0.24; 95% CI, 0.11-0.54; P = .0006). There was no significant difference in the incidence of complications between two groups. This meta-analysis summarises current evidence and indicates that PRP is a safe and effective adjuvant for skin graft enrichment.

Systematic review of the efficacy of fat grafting and platelet-rich plasma for wound healing

Adipose-derived stem cells found in fat grafts may have significant healing properties. When fat is combined with autologous platelet-rich plasma (PRP), there may be enhanced healing effects due to the pro-angiogenic and anti-inflammatory effects of PRP. This study aimed to evaluate the current evidence on fat grafting in combination with PRP for wound healing to establish the efficacy of this technique. A comprehensive search in the MEDLINE, EMBASE, CENTRAL, Science Citation Index, and Google Scholar databases (to March 2017) was conducted to identify studies on fat grafting and PRP for wound healing. Case series of less than 3 cases and studies only describing harvest technique were excluded. The database identified 571 articles, of which 3 articles that used a combination of fat and PRP for wound healing (1 RCT and 2 case series) were included in this review. A total of 69 wounds in 64 patients were treated with an average wound size of 36.32cm² . Of these, 67% of wounds achieved complete healing. When reported, the mean time to healing was 7.5 weeks for those who underwent a single treatment. There were no significant complications in any patients. The combination of fat grafting and PRP may achieve adequate wound healing with relatively quick wound healing time compared with standard wound management options. However, evidence is extremely limited, and further studies are required to evaluate its efficacy for wound healing.

Protocol for a systematic review of the efficacy of fat grafting and platelet-rich plasma for wound healing

BACKGROUND

The use of fat grafting as a reconstructive surgical option is becoming much more common. Adipose-derived stem cells found in fat grafts are believed to facilitate wound healing via differentiation into fibroblasts and keratinocytes and the release of pro-healing growth factors. Several small studies have shown a positive effect of fat grafting in healing of wounds of a variety of aetiologies. When fat is combined with autologous platelet-rich plasma (PRP), there may be enhanced healing effects. This may be due to the pro-angiogenic and anti-inflammatory effects of PRP. We aim to synthesise the current evidence on combination fat grafting and PRP for wound healing to establish the efficacy of this technique.

METHODS/DESIGN

We will conduct a comprehensive literature search in the MEDLINE, EMBASE, CENTRAL, Science Citation Index, and Google Scholar databases (up to July 2017) to identify studies on fat grafting and PRP for wound healing. All primary studies and systematic reviews of these studies will be included, except case reports and case series with fewer than three patients, to evaluate the outcome of fat grafting and PRP on wound healing either on its own or when compared to other studies. Primary outcome measures are expected to be the proportion of total wounds healed at 12 weeks and the average wound healing time (time for 100% re-epithelialisation). Expected secondary outcome measures are the proportion of wounds achieving 50% wound healing, the type of wound benefitting most from fat grafting, economic evaluation, health-related quality of life, and adverse events. Subgroup analysis will be performed for the proportions of wounds healed based on wound aetiology.

DISCUSSION

This review will provide robust evidence of the efficacy of fat grafting and PRP for wound healing. This is an emerging technique, and this review is expected to guide clinical practice and ongoing research aimed at improving wound care.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42016049881.

The application of platelet-rich plasma in the treatment of deep dermal burns: A randomized, double-blind, intra-patient controlled study

Platelet-rich plasma (PRP) is a fraction of blood with a platelet concentration above baseline. When platelets get activated, growth factors involved in wound healing are released. The application of PRP has shown good results in wound care, however, up to date no substantial research has been performed on the effect of PRP in burn treatment. This randomized double blind intra-patient controlled study investigates the effect of autologous PRP on wound healing in burns that require surgery with a meshed split skin graft (SSG). Fifty-two patients with various areas of deep dermal to full thickness burns, receiving surgery with a SSG were included after informed consent. Comparable study areas A and B (intra-patient) were appointed, randomized and either treated with a SSG and PRP or with a SSG alone. At day 5 to 7 postoperative, the epithelialization and graft take rate were assessed. Three, six, and twelve months postoperative, follow-up measurements were performed in the form of POSAS-questionnaires, DermoSpectroMeter, and Cutometer measurements. There was no statistically significant difference between the mean take rate nor the mean epithelialization rate at day 5-7 between the PRP-treated and control areas. However, PRP-treated wound areas showed more often better or equal epithelialization and take rates at day 5-7 than the standard treated areas. Minor effects were also seen in the reoperated and early operated subgroups. At 3, 6, and 12 months postoperative, POSAS scores from the patients and the observers, Dermaspectro-, and Cutometer measurements did not depict a significant difference between the PRP and standard treated areas. Concluding, the addition of PRP in the treatment of burn wounds did not result in improved graft take and epithelialization, nor could we demonstrate better scar quality. There was, however, a considerable variation in our clinical population.