Biomedical subjects

Brian S Bull

Publications and source records attributed to Brian S Bull.

7 recordsLinked to original sources

PubMed2004

Avoiding regression analysis pitfalls when calibrating white blood cell differential counters.

Method comparison and calibration are important for clinical hematologists and for manufacturers of new methods and instruments. Automation of the white blood cell (WBC) differential count poses unique problems in this regard because the reference method is a microscopic manual cell count of 200 WBCs. A highly variable reference method can obscure the true relation between the reference and the test methods and reduce sensitivity to miscalibration. A computer model based on published cell distributions and on the statistical properties of proportions was created to enable testing of alternative approaches to calibration. Ordinary linear regression (OLR) and standard Deming regression (SDR) were applied to a comparison of the results obtained with a virtual cell counter (counting 2,000 WBCs) and that obtained with a virtual 200-cell reference method for monocytes (mean population percentage of 7.1%) and lymphocytes (mean population percentage of 29%). Both regression approaches can misrepresent the known mathematical relation between the methods. This problem almost always occurs when OLR is used and the proportion of the cell of interest is low, as in the case of monocytes (7.1% of the total count). OLR comparisons, however, introduce significant error even for cell counts of 29%. SDR performed much better for both cell types.

Automation↗

PubMed2003

The effect of three commercial coaching courses on Step One USMLE performance.

BACKGROUND: A substantial industry exists to provide formal review courses for Step 1 of the United States Medical Licensing Examination (USMLE). There are limited data on the usefulness of these courses. AIM: To determine whether or not student participation in a commercial coaching course improves performance on Step 1 of the USMLE. METHODS: Scores achieved by 468 students on the National Board of Medical Examiners (NBME) Comprehensive Basic Science Examination (CBSE) were used to predict a score on Step 1 of the USMLE. The NBME is the organisation that prepares and administers the USMLE. Predicted USMLE scores were then regressed against the actual scores achieved by the students on Step 1. The students were divided into 2 groups: those who took a 3-4-week live commercial coaching course and those who studied on their own. RESULTS: The regression lines for the 369 students who studied on their own and the 99 students who took a commercial coaching course were statistically indistinguishable. The analysis was powerful enough to have picked up a difference of 1% on average (P = 0.05) or 2 questions out of the 350 constituting Step 1 of the USMLE. Neither the students who performed above average nor those who performed below average on the CBSE improved their performance on Step 1 as a result of the coaching courses. CONCLUSIONS: Students who take a live, 3-4-week commercial coaching course to improve performance on Step 1 of the USMLE do not achieve higher scores than students who study on their own. Students should strongly consider whether or not a substantial investment in time and money for a commercial coaching course is justified in the light of such meagre returns.

Curriculum↗

PubMed2002

Rapid-SF: a rapid whole-blood screen for soluble fibrin monomer.

Thrombosis accounts for a high proportion of disability and death in the West. Although soluble fibrin (SF) assays have been shown to be good predictors of thrombosis, current quantitative assays are too complex or lengthy to provide timely results, while simpler methods are qualitative and lack sensitivity. We here describe a rapid, new, protamine-based whole-blood screening method for SF which is quantitative and suitable for point-of-care use. Citrated whole blood is mixed with reagent under controlled conditions and the time until development of an SF precipitate is measured. Negative samples remain precipitate-free for 300 seconds. Strongly positive samples develop precipitate in as little as 10 seconds. SF times are mathematically converted to arbitrary SF units (SFU). This Rapid-SF test provides a simple and reliable means of detecting the presence of SF, and is well-suited for whole-blood rapid screening in the emergency department, operating room or clinic.

Fibrin↗

PubMedDate not supplied

Control of analyzer slope and intercept in the measurement of packed red cell volume (PCV): part I.

Five multichannel hematology analyzers (four different models) were evaluated to determine the ability of analyzers to correctly measure packed cell volume (PCV) values across the clinically relevant range. A sixth analyzer (fifth model) was subsequently included using archival data. Twenty-two different blood samples with PCVs ranging from 0.2 to 0.6 L/L were run in duplicate on each analyzer. Duplicate reference PCV determinations were also done using the recently described ICSH-recommended reference method. Simultaneously, a simpler "surrogate reference" procedure was performed in duplicate. Analyzer values were compared to ICSH reference and to surrogate reference PCV values using Deming regression analysis. Compared to either reference, all analyzers showed a slope of less than 1.0, thereby overestimating the PCV at 0.2 L/L and underestimating the PCV at 0.6 L/L to some extent. This outcome was surprising. Deming regression slopes would be expected to average at 1.0. Instruments whose slopes are significantly less than 1.0 will show decreased sensitivity to both anemic and polycythemic patients. We know of no inherent reason why multichannel analyzers should behave in this fashion.

Adult↗

PubMedDate not supplied

Control of analyzer slope and intercept in the measurement of packed red cell volume (PCV): part II.

A majority of packed cell volume (PCV) assays performed in the United States are performed by multichannel hematology analyzers rather than by centrifugation of blood samples in glass capillary tubes. PCV results from both analytical approaches were compared to the recently described ICSH reference method to determine the effect of assay slope on clinical utility. Though not controllable by the end user, the slope of the PCV assay versus the reference was satisfactory when performed in centrifuged glass capillaries. In the small sample of multichannel analyzers surveyed, only two of six machines functioned as well in this respect as did the glass capillaries. The worst of the unsatisfactory multichannel analyzers would have identified correctly only about half of the anemic and the polycythemic patients in the 12,623 males surveyed in the Third National Health and Nutrition Examination Survey (NHANES III). The performance on the females in this U.S. Department of Health and Human Services study would have been similarly poor. It is important that manufacturers of multichannel analyzers attend to the slopes of their PCV assays if the results are to be diagnostically useful.

Adult↗

PubMedDate not supplied

Reinfusion of aspirated pericardial blood during CPB. Part I. Hypothesis: laparotomy sponges are a significant part of the CPB circuit?

Blood accumulating in the pericardial sac is routinely reinfused during cardiopulmonary bypass (CPB) surgery. Such reinfusion has been associated with an increased incidence of serious complications such as coagulopathy, systemic inflammation, and neurologic sequelae. We hypothesize that some of these complications occur because the reinfused blood has been exposed to and activated by laparotomy sponges used to elevate the heart during vein graft emplacement. Such laparotomy sponges expose accumulating pericardial blood to a large, raw, cotton surface with an area approximately five times that of the CPB circuit (excluding the biocompatible oxygenator membrane). Because the reinfused blood has been exposed to this surface, the sponge becomes, in essence, a significant-though inapparent-part of the CPB circuit. Steps should be taken to either eliminate the sponge or to reduce the area of this foreign surface and make it more biocompatible.

Blood Loss, Surgical↗

PubMedDate not supplied

Reinfusion of aspirated pericardial blood during CPB. Part II. Laparotomy sponges are hazardous parts of the CPB circuit?

Usually, cotton laparotomy sponges are discarded when they become blood soaked. During bypass surgery, however, they are often wrung out into the pericardial sac and the contents of the sac are aspirated into the cardiopulmonary bypass (CPB) circuit. After cardiopulmonary bypass, many patients give evidence of mental confusion, excessive bleeding, and systemic inflammatory response syndrome (SIRS). We believe that a possible cause is reinfusion of blood that has been activated by contact with laparotomy sponges and contains fibrin microemboli and thrombin. Thrombin production, soluble fibrin (SF) development, and fibrinogen disappearance were measured, over time, in model systems composed of increasing amounts (0-10-20 microL) of tissue factor (TF) in 4 ml of anticoagulated blood distributed through the interstices of a 49-cm(2) laparotomy sponge. Clotting occurred in all of the sponges. Clotting was accelerated by the presence of TF. Without TF, clotting occurred in an average of 28 min (range 17-39). With 10 and 20 microl TF, clotting occurred in 20 (range 11-27) and 13 (range 10-16) min, respectively. Thrombin at a level of approximately 16 NIHU/ml whole blood was present in several donors for 10-20 min after clotting was complete. If 120 ml of blood was to be wrung from a full-sized laparotomy sponge at this point in time, it could contain as much as 2000 units of thrombin.

Blood Coagulation↗