Specific Correction Factors Research Articles

Inter-method variability in PTH measurement: Implication for the care of CKD patients

The National Kidney Foundation/Kidney-Dialysis Outcome Quality Initiative guidelines recommend to maintain the serum intact parathyroid hormone (PTH) concentration between 150 and 300 ng/l in chronic kidney disease (CKD) stage 5 patients. As these limits were derived from studies that used the Allegro intact PTH assay, we aimed to evaluate whether they were applicable to other PTH assays. We compared the PTH concentrations measured with 15 commercial immunoassays in 47 serum pools from dialysis patients, using the Allegro intact PTH assay as the reference. We also evaluated the recovery of graded amounts of synthetic 1-84 and 7-84 PTH added separately to a serum pool. Although the assays were highly correlated, the concentrations differed from one assay to another. The median bias between the tested assays and the Allegro intact PTH assay ranged from -44.9 to 123.0%. When the PTH concentrations were 150 or 300 ng/l with the Allegro intact PTH assay, they ranged with other assays from 83 to 323 ng/l and from 160 to 638 ng/l, respectively. The tested assays recognized 7-84 PTH with various cross-reactivities, whereas a given amount of 1-84 PTH was recovered differently by these assays. We found important inter-method variability in PTH results owing to both antibody specificity and standardization reasons. The unacceptable consequence is that opposite therapeutic attitudes may be reached in a single patient depending on the PTH assay used. We propose to use assay-specific decision limits for CKD patients, or to apply a correcting factor to the PTH results obtained with a given assay.

SU‐DD‐A1‐04: In Vivo Prostate IMRT Dosimetry With MOSFET Detectors Using Brass Build‐Up Caps

Purpose: To develop a general formalism with various correction factors to predict dmax entrance dose with the new hemispherical brass buildup caps to be used with MOSFET detectors in anterior prostate IMRT fields and thereby integrate in vivo IMRT dose measurement as part of routine QA process in IMRT radiotherapy Method and Materials: We have used the new wide energy hemispherical build‐up caps for this study. Due to its high density and high atomic number it provides the minimal amount of metal needed to achieve full build‐up at Dmax for a range of photon energies. We have developed a general formalism to predict Dmax entrance dose by applying necessary correction factors after studying the response of MOSFET with brass build up caps for energy, dose rate, dose reproducibility, SSD and patient specific IMRT correction factor. Results: In vivo Prostate IMRT dose measurements with MOSFET detectors using brass buildup caps was performed and compared against dose predicted by two different treatment planning systems. We used both 6 MV and 10 MV for this study and compared the in vivo MOSFET detector reading with dose predicted by Philips Pinnacle (6 MV) and CMS XiO (10 MV) treatment planning systems respectively. We achieved a overall accuracy of better than ± 5% on measured patient doses. Conclusion: Routine IMRT QA in most institutions today only involves verifying the optimized fluence map delivered to the patient in a test phantom at a certain preset depth. Based on our work here, we believe adding in vivo IMRT dosimetry with MOSFET detectors using the new brass build up caps along with routine fluence map verification in phantoms and MLC quality assurance offers greater accuracy and confidence in actual dose delivered to the patient.

Predictive value of clinical risk assessment tools and guidelines for 10-year coronary heart disease risk in practice-based primary care

Summary Background: Risk for developing myocardial infarction derived from risk tables in primary care subjects in Switzerland may over- or un- derestimate risk. Coronary calcifications may improve the performance of risk tables. Methods: We used coronary calcium score percentiles >50 (CS% >50) as a surrogate marker for 10-year myocardial infarction risk in a prospective cross-sectional monocenter study. CS% >50 was compared to several risk charts, was used to reclassify subjects in the intermediate risk category assessed by Fram- ingham risk scores (FRS), and was used to cal- culate a cohort specific correction factor for FRS and PROCAM. Results from risk charts were entered into the Bayes formula as the pretest risk estimates. Subjects in our cohort were 100 primary care patients with no known history of cardiovascular disease randomly selected from three primary care practices. Results: The sensitivity of FRS to detect CS% >50 was 47%, and specificity was 85%. NCEP III and Swiss guidelines had sensitivi- ties of 53% and 67%, respectively (p = ns), and specificities of 66% and 67% (p 50-derived post-test probabilities shifted 16 subjects (76%) into the low-risk cat- egory and 5 subjects (24%) into the high-risk category. Cohort-specific correction factors were 0.68 for FRS and 0.64 for PROCAM. Conclusions: For our Swiss German co- hort, FRS and PROCAM tended to overesti- mate risk. A biological risk marker (coronary calcifications) may allow improvement of risk prediction in primary care subjects with inter- mediate risk and also helps in the calculation of cohort-specific correction factors.

A Simple Estimate of the Effect of the Serum Albumin Level on the Anion Gap

Background: The serum anion gap (serum [Na⁺]-Cl^-]-[CO₂]) is still the first-line approach to metabolic acidosis. However, while it is generally acknowledged that hypoalbuminemia mandates a downward adjustment of the expected anion gap, a specific correction factor for the anion gap in the face of low serum albumin has never been demonstrated. Methods: We reviewed initial laboratory data from 432 consecutive patients admitted or transferred to the medical intensive care unit at Nassau County Medical Center over a 6-month period and correlated the serum albumin with the anion gap and the serum [tCO₂] using multivariate analysis. We looked at the anion gap as a function of <Delta> (albumin), the difference between normal and actual serum albumin, defined as 4.0 - measured serum albumin g/dl. We also assessed [tCO₂] as an independent variable. Results: For patients with normal or high serum tCO₂, the ratio of change in anion gap (<Delta> anion gap) to <Delta> (albumin) was 1.46 and 1.45, respectively. For patients with serum tCO₂ <22 mEq/l this ratio was 1.89. In the latter group, anion gap was best predicted taking both <Delta> (albumin) and serum tCO₂ into account: anion gap = 36.2 - serum tCO₂ - 2.3*<Delta> (albumin) (r = 0.71, p < 0.0001). Conclusion: For intensive care patients with normal or high serum tCO₂ (>21 mEq/l) a simple bedside adjustment of the anion gap by subtracting 1.5 times the difference between measured serum albumin and the 'normal' level of 4.0 g/dl gives a close estimate of the actual anion gap. For intensive care patients with serum tCO₂ <22 mEq/l, correction of the anion gap is well predicted by adding about twice the <Delta> (albumin) to the calculated gap.

Estimación de factores de corrección edad-mes de parto para producción de leche en ganado holstein en México

Valencia PM, Ruiz LFJ, Montalvo VH, Trejo VB, Keown JF, Van Vleck LD. Tec Pecu Mex. 2000;38(1)9-18. In order to estimate age-month multiplicative correction factors for milk production in Mexican Holstein cattle, 72,111 lactation records from 43,267 Holstein cows for the period 1970- 1997 were used. An animal model was used and it included all available genetic relationships among animals. Separate analysis were made to estimate correction factors for North, Central and South regions of Mexico. Correction factors currently used and those obtained in this study were different (P<0.001) for the three regions according to age and month of calving for each region. These results suggest that corrected milk production could be different using both groups of factors and results in genetic evaluation could be different. The large differences between current correction factors and those estimated in this study were found for cows with 18-40 months old, in January, and between correction factors for the North region with current correction factors for cows older than 70 months in April. Correction factors estimated in this study are probably more appropiate than current correction factors, because an animal model was used, more information was available and specific variances and correction factors were obtained for each region. It is convenient that new correction factors obtained in this study should be used to obtain Mexican Holstein genetic evaluations.

Use of Tracer Gas for Direct Calibration of Emission-Factor Measurements in a Traffic Tunnel

ABSTRACT Pollutant measurements in traffic tunnels have been used to estimate motor-vehicle emissions for several decades. The objective in this type of study is to use the traffic tunnel as a tool for characterizing motor vehicles rather than seeking a tunnel design with acceptably low pollutant concentrations. In the past, very simple aerodynamic models have been used to relate measured concentrations to vehicle emissions. Typically, it is assumed that velocities and concentrations are uniform across the tunnel cross section. In the present work, a vehicle emitting a known amount of sulfur hexafluoride (SF6) was driven repeatedly through a 730-m-long traffic tunnel in Vancouver, Canada. Comparing the measured SF6 concentrations to the known emission rates, it is possible to directly assess the accuracy of the simple tunnel aerodynamic models typically used to interpret tunnel data. Correction factors derived from this procedure were then applied to measurements of carbon monoxide and other pollutants to obtain gram-per-kilometer emission factors for vehicles. Although the specific correction factors measured here are valid only for the tunnel tested, the magnitude of the factors (up to two or more) suggests that the phenomena observed here should be considered when interpreting data from other tunnels.

On the computation and efficiency of a HBP-GM estimator some simulation results

We propose and test a specific correction factor which improves both the resampling and projection algorithm for approximating the minimum volume ellipsoid (MVE) estimator. Simulations show that a high-breakdown-point GM estimator, based among other things on these improved MVE-estimates of location and scatter (i) is little less efficient than OLS if data are free from outlying observations, but in most cases is much more efficient if outliers corrupt the data, (ii) is always more efficient than Rousseeuw's least median of squares (LMS) estimator, and (iii) is always superior to both LMS and OLS if both precision and efficiency are considered.

Cross-calibration of fat and lean measurements by dual-energy X-ray absorptiometry to pig carcass analysis in the pediatric body weight range

The objective of this study was to cross-calibrate measurements of body composition by dual-energy X-ray absorptiometry (DXA) with chemical analysis of carcasses of pigs in the pediatric range of body weight. Eighteen pigs (25.5 +/- 7.0 kg; 9.9-32.8% body fat) were scanned in duplicate by using DXA with a Lunar DPX-L densitometer in the pediatric medium and adult fast-detail scan modes. Pigs were then killed and their carcasses analyzed completely. Carcass lean and fat contents were highly correlated with DXA measurement in both scan modes (Pearson r values > 0.98). For lean mass, the relation between carcass content and DXA measures was not significantly different from the line of identity in the adult mode, but was in the pediatric mode. For fat mass, the relations between carcass content and DXA measures were significantly different from the line of identity in both the adult and pediatric modes. In duplicate scans, the reliability of DXA measures of lean mass and fat mass was excellent in both scan modes. Because neither the adult nor the pediatric scan mode provided accurate measures of fat and lean mass, we derived specific correction factors to improve the measurement of total fat and lean compartments, thereby calibrating the Lunar DPX-L to the laboratory standard of carcass analysis in pigs.

Direct and indirect estimates of Leaf Area Index (LAI) for lodgepole and loblolly pine stands

We compared direct and indirect estimates of leaf area index (LAI) for lodgepole and loblolly pine stands. Indirect estimates of LAI using radiative methods of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) did not correlate with allometric estimates for lodgepole pine, and correlated only weakly with litter-trap estimates for loblolly pine. The PCA consistently under-estimated LAI in lodgepole pine stands with high LAI, and over-estimated LAI in the loblolly pine stands with low LAI. We developed a physical model to test the hypothesis that the PCA may under-estimate LAI in high leaf area stands because of increased foliage overlap and, therefore, increased selfshading. Radiative estimates of LAI using the PCA for the physical model were consistenly lower than allometric measures. Results from the physical model suggested that increased foliage overlap decreased the ability of the PCA to accurately estimate LAI. The relationship between allometric and radiative measures suggested an upper asymptote in LAI estimated using the PCA. The PCA may not accurately estimate LAI in stands of low or high leaf area index, and the bias or error associated with these estimates probably depends on species and canopy structure. A species specific correction factor will not necessarily correct bias in LAI estimates using the PCA.

Validité de l'analyse des sacs fécaux pour l'étude du régime alimentaire des jeunes au nid de la linotte mélodieuse (Carduelis cannabina)

Diet was studied in nestlings of the European Linnet (Carduelis cannabina L.) by analysing fecal sacs, the only method that allows continuous sampling of the diet to the end of the nesting period. The validity of the method was tested by comparing the results of the analysis with the composition of the stomach contents of nestlings that died during nesting. This study was carried out in a moor surrounded by hedges, at Campénéac, in Brittany, France. There is a strong correlation between the mean composition of the fecal sacs and that of the stomach contents, but biases were found. Animal matter, which represents a minimal fraction of the food and is given only occasionally to the chicks during the first days of feeding, leaves practically no traces in fecal sacs. Moreover, a few species of seeds that are almost completely assimilated, e.g. Brassica napus and Euphorbia helioscopia, can be greatly underestimated in the analysis of fecal sacs. As these species may be at certain times the preferred food of the chicks, specific correction factors have been calculated to compensate for the biases. Our results indicate that by analysing the fecal sacs one can quickly identify and quantify the diet of nestlings and that with a relatively small number of samples; it constitutes therefore a reliable and rapid technique.[Journal translation]

FID response factors for aliphatic sulphur compounds at higher concentration levels

The molar responses and specific weight correction factors for 25 aliphatic sulphur compounds in the 10 μg range were measured with a hydrogen flame-ionisation detector. No abnormal behaviour was found with sufficiently high ratio air/H2. The molar response of the sulphides and disulphides is strictly proportional to the carbon number. For a certain organic residue the weight correction factor is proportional to the number of sulphur atoms (or the molecular weight). No destructive effects on the detector burner and no decrease of sensitivity were observed.

Amniotic fluid analysis in erythroblastosis fetalis: II. Quantitative bilirubin relationships

The concentration of a solution of bovine albumin was adjusted so that its spectral absorption was essentially the same as a sample of normal amniotic fluid whose total protein content was 0.20 Gm. per 100 ml. Known amounts of protein bilirubin were added to 10 samples of the bovine albumin solutions and the log ΔO.D.450 and O.D.450 were determined. A constant relationship between these measurements was observed and the log ΔO.D.450 was then related to the known concentrations of protein bilirubin by a specific correction factor. This factor was used to determine the bilirubin concentration of pathologic amniotic fluid samples.