Neuroscience-informed classification of prevention interventions in substance use disorders: An RDoC-based approach

Neuroscience has contributed to uncover the mechanisms underpinning substance use disorders (SUD). The next frontier is to leverage these mechanisms as active targets to create more effective interventions for SUD treatment and prevention. Recent large-scale cohort studies from early childhood are generating multiple levels of neuroscience-based information with the potential to inform the development and refinement of future preventive strategies. However, there are still no available well-recognized frameworks to guide the integration of these multi-level datasets into prevention interventions. The Research Domain Criteria (RDoC) provides a neuroscience-based multi-system framework that is well suited to facilitate translation of neurobiological mechanisms into behavioral domains amenable to preventative interventions. We propose a novel RDoC-based framework for prevention science and adapted the framework for the existing preventive interventions. From a systematic review of randomized controlled trials using a person-centered drug/alcohol preventive approach for adolescents, we identified 22 unique preventive interventions. By teasing apart these 22 interventions into the RDoC domains, we proposed distinct neurocognitive trajectories which have been recognized as precursors or risk factors for SUDs, to be targeted, engaged and modified for effective addiction prevention.

An Efficient Capsule-based Network for 2D Left Ventricle Segmentation in Echocardiography Images

The segmentation of cardiac chambers is essential for the clinical diagnosis and treatment of cardiovascular diseases. It is demonstrated that in cardiac disease, the left ventricle (LV) is extensively involved. Therefore, segmentation of the LV in echocardiographic images is critical for the precise evaluation of factors that influence cardiac function such as LV volume, ejection fraction, and LV mass. Although these measurements could be obtained by manual segmentation of the LV, it would be time-consuming and inaccurate because of the poor quality and low contrast of these images. Convolutional neural networks, commonly referred to as CNNs, have emerged as a highly favored deep learning technique for medical image segmentation. Despite their popularity, the pooling layers in CNNs ignore the spatial information and do not consider the part-whole hierarchy relationships. Furthermore, they require a large training dataset and a large number of parameters. Therefore, Capsule Networks are proposed to address the CNNs limitations. In this study, for the first time, an optimized capsule-based network for object segmentation called SegCaps is proposed to achieve accurate LV segmentation on echocardiography images applied to the CAMUS dataset. The result was compared against the standard 2D-UNet. The modified SegCaps and 2D-UNet achieved an average Dice similarity coefficient (DSC) of 84.48% and 83.28% on LV segmentation, respectively. The capabilities of the CapsNet led to an improvement of 1.44% in DSC with 92.77% fewer parameters than the U-Net. The results indicate that the proposed method leads to accurate and efficient LV segmentation.Clinical Relevance- From a clinical point of view, our findings lead to more precise evaluations of critical cardiac parameters, including ejection fraction as well as left ventricle volume at end-diastole and end-systole.

Psoriatic arthritis, axial spondyloarthritis and rheumatoid arthritis in Norway: nationwide prevalence and use of biologic agents

OBJECTIVE

To estimate the prevalence of psoriatic arthritis (PsA), axial spondyloarthritis (axSpA) and rheumatoid arthritis (RA) and the use of biologic agents in these diseases in Norway.

METHODS

From the Norwegian Patient Registry (NPR), we identified as PsA, axSpA and RA patients ≥18 years those with ≥2 recorded episodes with diagnostic coding for index disease (L40.5, M07.0-M07.3 for PsA; M45, M46.0, M46.1, M46.8 and M46.9 for axSpA; M05-M06 for RA). We calculated the point prevalence of PsA, axSpA and RA as per the 1^st of January 2017 in the Norwegian adult population (age ≥18). Dispensed disease-modifying antirheumatic drug (DMARD) prescriptions were obtained from the Norwegian Prescription Database and biologic DMARDs given in hospitals from the NPR.

RESULTS

The point prevalence of PsA, axSpA, RA, and any of these diseases in total was 0.46%, 0.41%, 0.78%, and 1.56%, respectively. Among women, the prevalence of PsA, axSpA, and RA was 0.50%, 0.37%, and 1.10%, and among men 0.43%, 0.45%, and 0.46%, respectively. In 2017, 27.3% of RA patients, 25.7% of PsA patients and 35.1% of axSpA patients used biologic DMARDs. Treatment with biologics was more frequent in younger age groups in all three diseases, and became more infrequent especially after age ≥55 years.

CONCLUSION

In Norway, the combined prevalence of PsA, axSpA, and RA was over 1.5%. Reflecting the good overall access to highly effective but costly biologic treatments, more than a fourth of these patients used biologic agents, which corresponds to over 0.4% of Norwegian adult population.

POS0516 PLASMA CALPROTECTIN WAS ASSESSED IN MULTIPLE BIOLOGICAL TREATMENT STRATEGIES FOR EARLY RHEUMATOID ARTHRITIS

Background

Plasma calprotectin is a sensitive inflammatory marker in patients with rheumatoid arthritis (RA) and reflects activation of granulocytes and macrophages. Plasma calprotectin has not previously been studied in a head-to-head trial of multiple biological mechanisms of action versus active conventional therapy (ACT) with methotrexate and prednisolone.

Objectives

To assess the effect of treatment on plasma calprotectin levels in patients with early RA by determining the 24-week change in the four arms of the NORD-STAR Study, a large multicenter randomized head-to-head clinical trial of ACT versus tumor necrosis factor inhibition, T-cell co-stimulation inhibition, and interleukin-6 inhibition (1).

Methods

Calprotectin was analyzed in plasma samples at baseline, week 4 and week 24 from 400 treatment naïve patients with early RA in the NORD-STAR Study. Samples were analyzed using a calprotectin ELISA alkaline phosphatase (ALP) kit from CalproLab (Oslo, Norway) in a Dynex DS2 processing system (normal levels <910 µg/L). Patients were assessed by clinical (CRP, 28 SJC/TJC, physician global) and patients’ reported assessments. Crude and adjusted linear regression analyses were performed in R 4.0.3 with calprotectin levels at week 24 as the outcome. The four arms were represented by three dummy variables. The adjustment variables were age, sex, anti-CCP status and country. Both analyses were adjusted for baseline calprotectin levels.

Results

At baseline, the mean time since diagnosis was 15.7 days (SD) (22.9), mean age 53.7 (15.0) years, ACPA positive 81%, and female 66%. Mean calprotectin levels were 1931 (1495) µg/L at baseline, 866 (951) µg/L at week 4, and 629 (661) µg/L at week 24. At baseline, normal calprotectin levels (<910 µg/L) were observed in 27% of all patients (ACT 22%, certolizumab-pegol and methotrexate 30%, abatacept and methotrexate 25%, tocilizumab and methotrexate 31%). At week 24, normal calprotectin levels were observed in 82% of all patients (ACT 68%, certolizumab-pegol and methotrexate 91%, abatacept and methotrexate 80%, tocilizumab and methotrexate 90%).

Observed calprotectin levels at week 24 were significantly lower in patients treated with certolizumab-pegol and methotrexate -336µg/L (97) (p< 0.006) or tocilizumab and methotrexate -284 (99) (p < 0.004), versus ACT when adjusted for age, sex, anti-CCP status, baseline calprotectin level, and country; however, a significant difference was not observed in patients treated with abatacept and methotrexate -110 (96) (p = 0.25). The Figure 1 shows the average percentage change in calprotectin levels from baseline to week 24 for all treatment groups.

Figure 1.

Average percentage change in calprotectin levels from baseline to week 24. ACT: active conventional therapy, CZP+MTX: certolizumab-pegol and methotrexate, ABA+MTX: abatacept and methotrexate, TCZ+MTX: tocilizumab and methotrexate.

Conclusion

Calprotectin, a sensitive biomarker of inflammation, normalized in the majority of patients. The decline differed between treatment groups and was largest in patients treated with a TNF inhibitor and methotrexate, suggesting that calprotectin reflects the activity of specific inflammatory pathways rather than overall inflammation. The findings of this study should be further explored.

References

[1]Hetland ML, et. al., Active conventional treatment and three different biological treatments in early rheumatoid arthritis: phase IV investigator initiated, randomised, observer blinded clinical trial. BMJ. 2020 Dec 2;371:m4328. doi: 10.1136/bmj.m4328. PMID: 33268527; PMCID: PMC7708829.

Acknowledgements

I would like to acknowledge the NORD-STAR Study group.

Disclosure of Interests

David Stevens: None declared, Marte Heiberg: None declared, Amirhossein Kazemi: None declared, Ronald van Vollenhoven: None declared, Jon Lampa: None declared, Anna Rudin: None declared, Kristina Lend: None declared, Merete Lund Hetland: None declared, Mikkel Østergaard: None declared, Michael Nurmohamed: None declared, Kim Hørslev-Petersen: None declared, Dan Nordström Consultant of: Abbvie, BMS, Lilly, MSD, Novartis, Pfizer, Roche and UCB, Björn Gudbjornsson: None declared, Till Uhlig: None declared, Espen A Haavardsholm: None declared, Hilde Berner Hammer Speakers bureau: AbbVie, Novartis, and Lilly.

Opium tincture for opioid substitution treatment

Introduction

Opium tincture (OT) is widely used for opioid substitution treatment (OST) in Iran.

Objectives

To determine if OT is a safe and effective medication for OST.

Methods

Opium Trial was a multicenter, double‐blind, noninferiority randomized controlled trial, with 204 participants with opioid dependence in Iran. Participants were then randomized to OT or methadone arms with an allocation ratio of 1:1 and were followed for 12 weeks. The primary outcome was retention in treatment, compared between the two groups using both intention-To-Treat (ITT) and Per-Protocol (PP) analyses.

Results

A total of 70 participants (IT: 68.6%, PP: 69.3%) in methadone arm and 61 participants (ITT: 59.8%, PP: 60.4%) in OT arm remained in the treatment. The relative retention rate was 1.15 (0.97, 1.36) in both analyses in favour of methadone. A total of 46 out of 152 (30.3%) participants in OT arm and 83 out of 168 (49.4%) participants in methadone arm reported opioid use outside the treatment. The difference in these two proportions (OT - methadone) was 19%: (10%, 28%) in favour of OT. The proportion of patients with adverse events were not different between the two arms (P = 0.06). There was no serious AE in OT arm.

Conclusions

Opium tincture is a clinically effective and safe medication, but this study could not conclude if it was as equally effective as methadone in retaining participants in treatment, but it showed that OT was superior to methadone in reducing opioid use outside the treatment.

Disclosure

No significant relationships.

Effect of probiotic and prebiotic versus placebo on appetite in patients with major depressive disorder: post hoc analysis of a randomised clinical trial

BACKGROUND

Poor appetite and weight loss are common in melancholic depression. Probiotics and prebiotics have the capacity to affect host behaviour, appetite and weight change by modulating the gut microbiome. The aim of this post hoc analysis was to investigate the effect of supplementation with probiotic and prebiotic on appetite, in parallel with body mass index (BMI), weight and energy intake, in patients with major depressive disorder (MDD).

METHODS

We extracted data from a clinical trial with 81 patients. The participants were randomly assigned to receive probiotic (Lactobacillus helveticus and Bifidobacterium longum), prebiotic (galactooligosaccharide) or placebo for 8 weeks. Appetite, weight, BMI, dietary intake, serum leptin and physical activity were measured. Subjective appetite rating was evaluated every 2 weeks using visual analogue scales (VAS) to assess satiety, hunger, fullness and desire to eat. Serum leptin was measured by an enzyme-linked immunosorbent assay. Physical activity was measured using the international physical activity questionnaire. A repeated measures analysis of variance model was used to analyse VAS data and analysis of variance/analysis of covariance models for dietary intake, BMI, weight and leptin data.

RESULTS

VAS data analyses indicated no significant intervention-time interactions but did show a significant increase over time for desire to eat within the probiotic group (P = 0.025). No significant difference in either BMI or weight was seen among the groups. Energy intake and leptin were significantly increased in the probiotic group compared to the prebiotic.

CONCLUSIONS

Overall, probiotic supplementation for 8 weeks among MDD patients resulted in improvement of appetite, whereas prebiotic administration had no significant effect on appetite.

The effects of weight loss approaches on bone mineral density in adults: a systematic review and meta-analysis of randomized controlled trials

We assessed the impact of weight loss strategies including calorie restriction and exercise training on BMD in adults using a systematic review of randomized controlled trials. Weight reduction results in reduced BMD at the hip, but has less effect on the spine. Both calorie restriction and a combination of calorie restriction and exercise result in a decrease in hip bone density, whereas weight loss response to exercise training without dietary restriction leads to increased hip BMD.

INTRODUCTION

Findings are not consistent on the effect of weight loss on bone mineral density (BMD). We conducted a systematic review on the randomized controlled trials to assess the effect of weight loss strategies, including calorie restriction and exercise programs on BMD in adults.

METHODS

A structured and comprehensive search of MEDLINE and EMBASE databases was undertaken up to March 2016. Study-specific mean differences (MD) were pooled using a random-effects model. Subgroup analysis and meta-regression were used to find possible sources of between-study heterogeneity.

RESULTS

Thirty-two randomized controlled trials met predetermined inclusion criteria. The meta-analysis revealed no significant difference on total BMD (MD 0.007, 95 % CI -0.020-0.034, p = 0.608). In contrast, the pooled data of studies showed a significant effect of weight loss on hip BMD (MD -0.008, 95 % CI -0.09 to -0.006 g/cm(2), p < 0.001) and also lumbar spine BMD (MD -0.018 g/cm(2), 95 % CI -0.019 to -0.017, p < 0.001). BMD in the hip site decreased after more than 4 months, especially in those who were obese. Moreover, calorie restriction interventions longer than 13 months showed a significant decreased in lumbar spine BMD.

CONCLUSION

Weight loss led to significant decreases at the hip and lumbar spine BMD but not at the total. Weight loss response following calorie restriction resulted in a decrease in hip and lumbar spine bone density especially more than 1 year; whereas an exercise-induced weight loss did not.

Endocarditis associated with Erysipelothrix rhusiopathiae in a fat-tailed ram

Endocarditis is rarely reported in sheep and information presented for ovine endocarditis is based mostly on comparative findings in the cattle. Infective vegetative endocarditis of the right heart was diagnosed in a 3-year-old fat-tailed ram. Clinical findings included tachycardia, marked brisket edema, jugular veins distention and pulsation and pale mucous membranes. Hematologic abnormality included neutrophilic leukocytosis. Necropsy confirmed severe right atrioventricular and pulmonary valves vegetative endocarditis with evidence of right heart failure. Erysipelothrix rhusiopathiae was isolated from those vegetative lisions.

Endovascular treatment of symptomatic intracranial atheromatous stenosis: a single center study of 21 consecutive cases

OBJECTIVES

This retrospective single-center study evaluated the technical success as well as the periprocedural and long-term complications of angioplasty with stenting of symptomatic intracranial atheromatous stenosis.

PATIENTS AND METHODS

From January 2005 to December 2010, 21 patients were treated by angioplasty with stent implantation for symptomatic atheromatous intracranial stenosis greater or equal to 50% at least 7 days after a stroke.

RESULTS

The median population age was 65 years (range: 41-88 years), and 76% (16/21) of the candidates had a history of transient ischemic attack (TIA) or stroke before the event qualifying them for an endovascular procedure. In addition, 86% (18/21) were taking antithrombotic medication at the time of the qualifying event. Technical success was obtained in all cases. The periprocedural stroke or death rate was 9.5% (2/21), and there was no other stroke or death after 30 days during the mean follow-up of 1.4 years.

CONCLUSION

Endovascular treatment of symptomatic intracranial atherothrombotic stenosis can lead to severe complications, particularly during the periprocedural period, but it also represents the only alternative treatment for patients who fail with medical therapy. Future studies need to focus on improvement of periprocedural complications. Essentially, this should include more rigorous selection of candidates as well as a better understanding of the pathophysiological mechanism(s) of the ischemic phenomenon related to stenosis.

Isolation and characterization of some moderately halophilic bacteria with lipase activity

Lipases are an important class of enzymes which catalyze the hydrolysis of long chain triglycerides and constitute the most prominent group ofbiocatalysts for biotechnological applications. There are a number of lipases, produced by some halophilic microorganisms. In this study, some lipase producing bacteria from Maharlu salt lake located in south of Iran were isolated. All isolates were screened for true lipase activity on plates containing olive oil. The lipase activity was measured using titrimetric methods. Among thirty three isolates, thirteen strains demonstrating orange zone around colonies under UV light, were selected for identification using the molecular methods and some morphological characteristics. The bacterium Bacillus vallismortis BCCS 007 with 3.41 +/- 0.14 U/mL lipase activity was selected as the highest lipase producing isolate. This is the first report of isolation and molecular identification of lipase producing bacteria from Maharlu lake.

Classification of Iranian patients with Glanzmann's Thrombasthenia using a flow cytometric method

Glanzmann's Thrombasthenia (GT) is a rare inherited autosomal recessive platelet disorder caused by a deficiency or dysfunction of the GPIIb-IIIa receptor on platelets, which is characterized by a lack of platelet aggregation in response to multiple physiologic agonists and a life-long bleeding disorder. Flow cytometry is a rapid and highly sensitive method that can detect reduced levels of receptors, as well as absolute deficiency. The aim of this study was to classify Iranian GT patients by a flow cytometric method, and to correlate these findings with the severity of clinical bleeding. The expression of GPIIb-IIIa on the platelet surface was assessed in 123 GT patients using quantitative flow cytometry to determine the most common subtype among these patients. We used a panel of antibodies to detect the expression of glycoproteins GPIb, GPIIb, GPIIIa, as well as Integrin αv. Patients were also interviewed with regard to the severity and frequency of bleeding, according to history and gender, in order to evaluate the nature of their bleeding phenotype, and classify them as mild, moderate or severe bleeders, in accordance with the Glanzmann's Thrombasthenia Italian Team (GLATIT) protocol. In the detailed analysis of the results of our investigation, 95 out of 123 (77.5%) were classified as type I; 20 (16%) as type II with residual GPIIb-IIIa, and eight (6.5%) as GT variants. The variant type was diagnosed by the inability of GPIIb-IIIa to bind fibrinogen, as evidenced by the absence of platelet aggregation in response to physiologic agonists. There was no significant correlation between bleeding severity and different subtypes of GT. This study demonstrates that GT type I is the most common subtype among Iranian patients. There was no correlation between severity of symptoms and cytometric phenotype of the disease. The identification of families at risk may significantly decrease the incidence of the severe form of the disorder if genetic counseling is provided.

Effect of Fe2+ and Fe3+ ions on human plasma cholinesterase activity

OBJECTIVES

Metals such as iron are needed for physiological functions of the body. However, their excess may cause serious damage including poisoning. The effects of Fe2+ and Fe3+ ions on human plasma cholinesterase activity were investigated.

MATERIAL AND METHODS

Plasma were obtained (n = 24) from healthy male volunteers, and treated with five various concentrations of Fe2+ and Fe3+ ions. Activity of butyryl cholinesterase (BChE) was assayed according to colorimetric EIIman procedure. The activity was calculated as micromole of hydrolyzed substrate, per minute in each ml.

RESULTS

Both ferric (Fe3+) and ferrous (Fe2+) ions significantly decreased the BChE activity in all tested concentrations. The effect of ferric (Fe3+) ions on the reduction of plasma enzyme activity was more pronounced than ferrous (Fe2+) ions (p < 0.001, respect to control group).

CONCLUSIONS

The present paper represents the effect of Fe2+ and Fe3+ ions on ButyrylChE activity in human plasma. It reveals that both ions suppress BChE activity.

pH of pus collected from periapical abscesses

AIM

To determine the pH of pus collected from periapical abscesses.

METHODOLOGY

Forty patients (Male = 17/Female = 23) between the ages 17 and 37 years, each with a periapical abscess and with no relevant medical history, were recruited. All the participants had moderate-to-severe pain on percussion accompanied by localized or generalized swelling. At least 1 mL of pus was aspirated from each participant using a No 20 gauge needle. A pH meter was used to define the pH of the pus immediately following aspiration.

RESULT

The mean pH of pus from the periapical abscesses of patients was 6.68 +/- 0.324 with a range between 6.0 and 7.3. There was no statistically significant difference in pH by gender or age.

CONCLUSION

The mean pH of pus from periapical abscesses was generally acidic, but some samples (two female and three male) were neutral and some samples (four female and one male) were alkaline.

Cholesteryl ester transfer protein I405V polymorphism influences apolipoprotein A-I response to a change in dietary fatty acid composition

The aim of the present study was to investigate whether the cholesteryl ester transfer protein (CETP) I405V polymorphism modifies the response to changes in the dietary ratio of polyunsaturated to saturated fat (P:S). The population included 85 healthy subjects with the different I405V genotypes (35 II, 36 IV, and 14 VV) assigned to two consecutive 28-day experimental period. All subjects consumed a high-P:S with P:S of 1.2 for the first period and a low-P:S with a P:S of 0.3 for the next 28-day period. At the first and end of each dietary period, serum lipid, lipoprotein, and CETP concentrations were measured. At screening, lipid or lipoprotein concentrations were not significantly different among CETP I405V genotype groups. After the low-P:S diet, subjects carrying V allele had greater reduction in apoA-I and HDL cholesterol (HDL-C) than subjects with II genotype. A genotype-by-diet interaction effect was observed on apoA-I (p=0.016) concentrations. In conclusion, the CETP I405V polymorphism contributes to the unfavorable changes of apoA-I and HDL-C when a high-P:S diet was replaced with a low-P:S diet.

Serum level of anti-hepatitis B surface antigen 6-8 years after hepatitis B vaccination at birth

The duration of protection after hepatitis B vaccination in children is unknown. We determined the serum level of antibody to hepatitis B surface antigen (anti-HBsAg) in 273 randomly selected 7-9-year-old schoolchildren from Zanjan City, Islamic Republic of Iran, who had been fully vaccinated against hepatitis B starting at birth. Titres < or = 10 mlU/mL were considered unprotective. Just over half of the children (52%) had titres < or = 10 mlU/mL with no difference between the sexes, while 81 (29.7%) had no anti-HBsAg (0 mlU/mL). Three of the children had antibodies to hepatitis B core protein. More studies are needed to determine the necessity for or timing of booster doses.

Combination of gastric atrophy, reflux symptoms and histological subtype indicates two distinct aetiologies of gastric cardia cancer

INTRODUCTION

Atrophic gastritis is a risk factor for non-cardia gastric cancer, and gastro-oesophageal reflux disease (GORD) for oesophageal adenocarcinoma. The role of atrophic gastritis and GORD in the aetiology of adenocarcinoma of the cardia remains unclear. We have investigated the association between adenocarcinoma of the different regions of the upper gastrointestinal tract and atrophic gastritis and GORD symptoms.

METHODS

138 patients with upper GI adenocarcinoma and age- and sex-matched controls were studied. Serum pepsinogen I/II was used as a marker of atrophic gastritis and categorised to five quintiles. History of GORD symptoms, smoking and H pylori infection were incorporated in logistic regression analysis. Lauren classification of gastric cancer was used to subtype gastric and oesophageal adenocarcinoma.

RESULTS

Non-cardia cancer was associated with atrophic gastritis but not with GORD symptoms; 55% of these cancers were intestinal subtype. Oesophageal adenocarcinoma was associated with GORD symptoms, but not with atrophic gastritis; 84% were intestinal subtype. Cardia cancer was positively associated with both severe gastric atrophy [OR, 95% CI: 3.92 (1.77 to 8.67)] and with frequent GORD symptoms [OR, 95% CI: 10.08 (2.29 to 44.36)] although the latter was only apparent in the non-atrophic subgroup and in the intestinal subtype. The association of cardia cancer with atrophy was stronger for the diffuse versus intestinal subtype and this was the converse of the association observed with non-cardia cancer.

CONCLUSION

These findings indicate two distinct aetiologies of cardia cancer, one arising from severe atrophic gastritis and being of intestinal or diffuse subtype similar to non-cardia cancer, and one related to GORD and intestinal in subtype, similar to oesophageal adenocarcinoma. Gastric atrophy, GORD symptoms and histological subtype may distinguish between gastric versus oesophageal origin of cardia cancer.

An in-vitro direct chemiluminescence assay for assessment of platelet-bound antibody in thrombocytopenic patients

A direct chemiluminescence test (CLT) employing autologous monocytes and granulocytes was used to assay platelet-bound antibody in comparison to the direct platelet suspension immunofluorescence test (PSIFT) in 50 patients. Twenty-six of the 30 immune thrombocytopenic purpura (ITP) patients, including all 21 chronic ITP patients with platelet counts below 100 x 10(9)/l, showed positive results with at least one type of phagocytic cell; so did seven of the eight patients with other presumed autoimmune thrombocytopenias, and three out of 12 patients with thrombocytopenia associated with non-immune disorders. This test appears potentially valuable in the clinical diagnosis of immune thrombocytopenias.

Platelet separation from the blood of severely thrombocytopaenic patients

An efficient method is described for the isolation of platelets from the blood of severely thrombocytopaenic patients. The method, based on centrifugation over a density medium, was compared with platelet-rich plasma obtained by conventional differential centrifugation at a relative centrifugal force of 200 x g. With samples from thrombocytopaenic patients (n = 10, platelet counts between 7 and 22 x 10(9)/l), the density barrier method gave significantly improved platelet recoveries (82.1% +/- 6.2%) compared with differential centrifugation (61.6 +/- 4.6%) (P less than 0.001). Platelets isolated by the density barrier method showed no tendency to aggregate and were suitable for use in tests to detect platelet-associated immunoglobulin.