Sampling distributions of p(pos) and p(neg)

Influence of the glycation gap on the diagnosis of type 2 diabetes

AIMS

The results of using HbA1C-based criteria for diagnosis of type 2 diabetes and prediabetes have been reported to differ from those obtained using fasting plasma glucose (FPG) or an oral glucose tolerance test (OGTT). We aimed to determine whether these discrepancies might be due to the influence of the glycation gap.

METHODS

For 430 patients without previously diagnosed diabetes for whom an OGTT had been requested in normal clinical practice, FPG, fructosamine and HbA1C were measured at the time of the test and again 1 month later. Glycaemia/diabetes status was classified as normoglycaemia, prediabetes or diabetes using both HbA1C-based and FPG/OGTT-based criteria, and their glycation gaps GG were calculated.

RESULTS

The specificity of an HbA1C level of 6.5 % (48 mmol/mol) for diagnosis of FPG/OGTT-defined type 2 diabetes was 99 %, but its sensitivity was less than 37 %. HbA1C-diabetic patients had higher average blood glucose levels than FPG/OGTT-diabetic patients. With either set of criteria, high-GG patients were disproportionately numerous among those classified as diabetic and were disproportionately infrequent among those classified as normoglycaemic, but the effect was greater for the HbA1C criteria.

CONCLUSIONS

The differences between HbA1C-based and FPG/OGTT-based diagnoses are largely due to the influence of the glycation gap, which may also influence the early stages of FPG/OGTT-defined diabetes.

Molecular and serological markers of Leishmania donovani infection in healthy individuals from endemic areas of Bihar, India

OBJECTIVES

Recent epidemiological reports indicate that asymptomatic human infections with Leishmania donovani, the causative agent of visceral leishmaniasis or Kala-azar (KA), occur frequently in India. We explored markers of infection.

METHODS

Blood samples were collected from 286 healthy subjects from 16 villages in the Muzaffarpur district of Bihar. These individuals were classified into three groups: (i) persons with no history of KA and living in a house where no KA cases were previously reported, (ii) persons with no history of KA but living in a house where KA cases were diagnosed at the time of sampling or in the past, and (iii) successfully treated KA patients. Each sample was tested using a Leishmania-specific PCR to detect Leishmania DNA, and two serological tests to demonstrate anti-Leishmania antibodies: the Direct Agglutination Test and rK39 ELISA.

RESULTS

PCR positivity was similar among the three groups (20-25%). In contrast, among treated patients, the percentage of serologically positive individuals was roughly five times that of healthy individuals with no KA history, as measured with either test. Living in a house where KA had been reported did not affect seropositivity.

CONCLUSION

A significant proportion of asymptomatic infections of Leishmania exist in endemic regions. Using a combination of molecular and serological tests increases the capacity to detect infections at different stages. Further work is required to understand the kinetics of the markers.

Inter-observer variability in chest radiograph reading for diagnosing acute lung injury in children

Acute lung injury (ALI), including its most serious form called acute respiratory distress syndrome (ARDS), is a devastating disease that can occur at any age. ALI/ARDS accounts for only 5-8% of admissions to pediatric intensive care units (PICUs) but is fatal in 30-60% of cases. International multicenter prospective studies are needed to better understand pediatric ALI/ARDS. However, a reproducible definition of ALI/ARDS is crucial to ensure that study populations are homogeneous. We designed a retrospective review to test the inter-observer variability of chest radiograph interpretation for presence of the American-European Consensus Conference (AECC) radiographic criterion for ALI/ARDS. The medical files of 24 children ventilated for ALI/ARDS in our PICU between January 1993 and December 2002 were reviewed. Five pediatric radiologists and five pediatric intensivists interpreted one frontal chest radiograph (FCR) per patient taken on the day of ALI/ARDS diagnosis. Each reader indicated whether the radiograph showed the AECC radiographic criterion for ALI/ARDS. Data analysis involved comparing each reader to all the others based on the raw agreement and Kappa coefficient (kappa). Features in the 24 patients were consistent with earlier studies. Global inter-observer agreement beyond chance was fair (kappa = 0.29 +/- 0.02) among the five radiologists (kappa = 0.26 +/- 0.05) and among the five intensivists (kappa = 0.29 +/- 0.05). Thus, considerable inter-observer variability occurred in assessing the radiographic criterion for ALI/ARDS, as previously shown in adults. Given the low incidence of ALI/ARDS in children, this variability may have a large impact in studies of pediatric ALI/ARDS.

The Genetics of Generalized Osteoarthritis (GOGO) study: study design and evaluation of osteoarthritis phenotypes

PURPOSE

The primary goal of the Genetics of Generalized Osteoarthritis (GOGO) study is to identify chromosomal regions associated with increased susceptibility to generalized osteoarthritis (OA). Here we describe the study design and phenotype of the 2728 participants from the 1145 families recruited for this study.

METHODS

GOGO is an investigator-initiated collaboration involving seven clinical academic sites and sponsored by GlaxoSmithKline. Family ascertainment was carried out between 1999 and 2002. A qualifying family required self-reported Caucasian ethnicity and at least two affected siblings with clinical hand OA. We hypothesized that this clinical phenotype would facilitate identification of participants with multijoint radiographic OA (rOA) in and beyond the hand. The "gold standard" case definition, however, was based on rOA (Kellgren-Lawrence grade > or =2) involving > or =3 hand joints distributed bilaterally and including at least one distal interphalangeal joint, with two of the three involved joints within a joint group (distal interphalangeal, proximal interphalangeal, or carpometacarpal). Radiographs of hips, knees and spine were also obtained. Additional siblings and living parents from qualifying families, both affected and unaffected, were invited to participate.

RESULTS

A total of 2706 participants had complete clinical and radiological examination data. Of these, 2569 participants met clinical examination criteria for affected status; while 1963 (73%) participants met the prespecified radiographic criteria for affected status. This corresponded to a total of 707 families with at least two affected siblings that met the hand rOA criteria. Of those individuals with rOA of the hand, the frequency of rOA at other sites was highest for the knee (51%) and spine (54%), and less common for the hip (25%). Concordance rates among hand affected siblings were greatest for spine (36%) followed by knee (31%) and hip (9%); a total of 53% of the affected sib pairs were concordant for specific patterns of generalized rOA involving the hand and large joints (knees, hips or spine).

CONCLUSIONS

GOGO represents a large multicenter collection of families with multiple joint OA that have been characterized both clinically and radiographically. The GOGO study will employ a comprehensive strategy for genetic screening based upon both qualitative and quantitative radiographic trait analyses, circulating biomarkers in a quantitative trait-based analysis, fine mapping, and candidate gene analysis. This sample should provide sufficient power to detect linkage to OA associated genes.

Approximate standard errors and confidence intervals for indices of positive and negative agreement

Indices of positive and negative agreement for observer reliability studies, in which neither observer can be regarded as the standard, have been proposed. In this article, it is demonstrated by means of an example and a small simulation study that a recently published method for constructing confidence intervals for these indices leads to intervals that are too wide. Appropriate asymptotic (i.e., large sample) variance estimates and confidence intervals for the positive and negative agreement indices are presented and compared with bootstrap confidence intervals. We also discuss an alternative method of interval estimation motivated from a Bayesian viewpoint. The asymptotic intervals performed adequately for sample sizes of 200 or more. For smaller samples, alternative confidence intervals such as bootstrap intervals or Bayesian intervals should be considered.