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L Tardella

Publications and source records attributed to L Tardella.

5 recordsLinked to original sources
PubMed1999

A Bayesian hierarchical approach for combining case-control and prospective studies.

Motivated by the absolute risk predictions required in medical decision making and patient counseling, we propose an approach for the combined analysis of case-control and prospective studies of disease risk factors. The approach is hierarchical to account for parameter heterogeneity among studies and among sampling units of the same study. It is based on modeling the retrospective distribution of the covariates given the disease outcome, a strategy that greatly simplifies both the combination of prospective and retrospective studies and the computation of Bayesian predictions in the hierarchical case-control context. Retrospective modeling differentiates our approach from most current strategies for inference on risk factors, which are based on the assumption of a specific prospective model. To ensure modeling flexibility, we propose using a mixture model for the retrospective distributions of the covariates. This leads to a general nonlinear regression family for the implied prospective likelihood. After introducing and motivating our proposal, we present simple results that highlight its relationship with existing approaches, develop Markov chain Monte Carlo methods for inference and prediction, and present an illustration using ovarian cancer data.

Bayes Theorem↗
PubMed1983

Red blood cell age, pyruvate kinase activity, and insulin receptors. Evidence that monocytes and RBCs may behave differently.

Data emerging from insulin receptor studies performed on red blood cells (RBCs) and monocytes from the same subject are not always in agreement; dichotomy might occur since variations in mean RBC age are not taken into account or because insulin receptors on the two cell types behave differently. In the present investigation RBCs from normal male subjects were separated into five populations of different mean age by means of centrifugation of RBCs on a discontinuous gradient of buffered Percoll for 10 min at 1000 X g. Insulin binding varied significantly depending upon the RBC population tested and was closely correlated to the activity of pyruvate kinase (r2 = 0.86), a well-known marker of RBC age. These data suggested that pyruvate kinase assay might be helpful in studies of RBCs. To confirm this hypothesis, RBCs from 10 normal male subjects and 13 male patients with hemolytic anemia were studied; insulin binding was correlated to pyruvate kinase activity. By adjusting insulin binding to 2 X 10(9) RBCs/ml the range of data was abnormally high, but it became acceptable after adjusting insulin binding to pyruvate kinase activity (0.75 U/2 X 10(9) RBCs). The overall data indicated that insulin binding was highly correlated to pyruvate kinase activity (r2 = 0.82) but only slightly to reticulocyte number (r2 = 0.56) since not only reticulocytes but also erythrocytes lose receptors during maturation. Pyruvate kinase activity was measured in RBCs from normal men and from normally menstruating women at the seventh and twenty-fourth days of the cycle; results demonstrated that adjustment of data, according to mean RBC age, broadens dichotomy of monocyte and RBC data.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Circulating anti-insulin receptor antibodies in a patient suffering from lupus nephritis and hypoinsulinemic hypoglycaemia.

A 46-year-old female patient suffering from Lupus Nephritis came to our attention in 1981 for severe recurrent hypoglycaemia; she was obliged to eat every 5-7 hr to maintain glucose values not below 1.3-1.6 mM. All known causes of hypoglycaemia were excluded by performing selective angiography of the pancreas and skull, chest and abdominal computerized tomography, as well as stimulation and suppression tests. Oral glucose tolerance, tolbutamide and intravenous insulin (0.4 U/Kg b.w.) tests demonstrated that the patient was highly insulin resistant; furthermore, studies on the patient's red blood cells suggested that her insulin receptors were completely unable to bind insulin. Studies carried out to reveal the reason for this binding inhibition demonstrated that red blood cells from normal subjects as well as adipocytes from normal rats incubated with the patient's serum did not bind insulin (50% inhibition occurring at about 1:30 serum dilution). Insulin binding inhibitors were found in the fraction of the serum precipitated by ammonium sulphate. The serum cleared of IgG fraction was unable to affect insulin binding. These data demonstrate that the serum from the female patient investigated contained anti-insulin receptor antibodies blocking the binding of insulin to its receptors. Plasmapheresis improved the patient's metabolic status. The clinical picture would suggest that recurrent hypoglycaemia was caused by anti-insulin receptor antibodies acting as insulin on target cells.

Autoantibodies↗
PubMed1982

Factor VII in liver cirrhosis.

Factor VII activity and factor VII cross-reacting material (CRM) in plasma of patients with liver cirrhosis have been studied before and after vitamin K1 parenteral administration. Subjects were divided into two groups according to the absence (group I) or the presence (group II) of the following clinical findings: ascites, portal hypertension, encephalopathy. Factor VII activity and CRM show a statistically significant correlation (p less than 0.001) in all patients. In group II, significantly reduced levels of both activity and CRM were found as compared to the reference and the group I values. No variations were found after vitamin K administration. Different thromboplastins, investigated with respect to their sensitivity for factor VII, acted differently. Patients with normal albumin levels also showed normal levels of factor VII activity and antigen. No correlation was found in group II. The data discussed suggest that in liver cirrhosis with unknown aetiology no immunologically detectable precursor of factor VII is present.

Adult↗