Transcutaneous bilirubin measurement

The development of transcutaneous measurements of medically important diagnostic data is a worthy endeavor intended to eliminate the need for invasive procedures. This paper reports success in meeting those ends with a clinical instrument for transcutaneous bilirubin measurement. The need for this device and technologic developments leading to such a device are described. The transcutaneous bilirubin meter exhibits a high degree of correlation with serum bilirubin levels and can be used for screening.     

An automated method for serum bilirubin determination

A method for the determination of both direct and indirect serum bilirubin on the AutoAnalyzer is described which has a number of advantages over the automated method that is currently recommended. It gives total bilirubin results which are similar to those obtained with the equivalent manual method and direct bilirubin results which are usually about 10% lower.     

Modification of Michaëlsson''s method for the measurement of plasma total bilirubin

Michaëlsson''s (1961) method for the measurement of plasma bilirubin concentration was found to be complicated by conjugated bilirubin. Delaying the addition of the accelerator, diphylline, corrected this fault. The method was calibrated using serum or plasma, since reconstituted protein solutions introduced large errors.     

Efficacy of using total bilirubin values as a guide for screening direct bilirubin requests

Two divergent laboratory approaches to the determination of direct bilirubin were assessed. The first approach, assaying direct bilirubin (DB) on all total bilirubin (TB) requests regardless of TB values, resulted in a true negative rate (normal TB level less than 1.0 mg/dL [less than 17 mumol/L], and DB level, less than 0.4 mg/dL [less than 6.8 mumol/L]) of 98.7% (984/997 specimens) and a low false negative (normal TB level, abnormal DB level) rate of 1.3% (13 of 997). The second approach, assaying DB on physician request and only if the TB level was greater than or equal to 1.0 mg/dL (1.7 mumol/L), resulted in a true negative rate (normal TB level, no liver disease) of 87.7% (150%) of 171 patients) and a relatively low false negative rate (normal TB level, liver disease) of 12.3% (21 of 171) patients. Medical chart review revealed that, with either approach, none of the patients with false negative results with hepatobiliary disease would have been missed clinically, even if the DB assay had not been done. It is possible to screen DB requests using a TB of 1.0 mg/dL (17 mumol/L) as a means to determine whether DB should be assayed.     

Evaluation of transcutaneous bilirubin measurement and agreement with bilirubinemia

Evaluation of the neonates for jaundice and kernicterus is indispensable when early hospital discharge has become standard practice. Transcutaneous bilirubin (TcB) measurement is an advantageous option because of its non-invasive nature and the possibility of its use near the patient. The point of care device BiliCheck has been compared in numerous instances to serum bilirubin. However, its clinical utility remains a subject of discussion. We have compared total blood bilirubin (TBB) concentrations to TcB values using the BiliCheck in newborns at 48 +/- 12 hours of life, at the time of discharge when they have lost weight. One hundred and ninety-six term neonates were initially included into the study. Transcutaneous bilirubin could be compared to whole blood bilirubin for 178 of them. Methods were compared by linear regression analysis and by the non-parametric Bland and Altman method. The correlation between BiliCheck and whole blood bilirubin was adequate (r(2): 0.7768). However, the Bland-Altman analysis revealed a 95% CI of -50.4 to 47.5 micromol/L. Transcutaneous bilirubin was also compared to a measure on plasma in a sub-group of 53 infants, the correlation was 0.7749 with a 95% CI of -35.8 to 46.5 micromol/L. Comparing total blood bilirubin with plasma bilirubin in 35 patients, we observed a similar results with a correlation of 0.7583 and a 95% CI of -34.6 to 40.7 micromol/L. Finally, the extent of weight loss observed in our group of patients had little influence and did not affect the agreement between the 2 approaches. We conclude that the BiliCheck may be used to monitor bilirubin in term neonates at 48 hours of life even with a weight loss. Clinicians have however to be conscious of the limit of the precision of the measures both for the BiliCheck and the laboratory methods.     

Noninvasive total hemoglobin measurement

Wavelength selection and prediction algorithm for determining total hemoglobin concentration are investigated. A model based on the difference in optical density induced by the pulsation of the heart beat is developed by taking an approximation of Twersky's theory on the assumption that the variation of blood vessel size is small during arterial pulsing. A device is constructed with a five-wavelength light emitting diode array as the light source. The selected wavelengths are two isobestic points and three in compensation for tissue scattering. Data are collected from 129 outpatients who are randomly grouped as calibration and prediction sets. The ratio of the variations of optical density between systole and diastole at two different wavelengths is used as a variable. We selected several such variables that show high reproducibility among all variables. Multiple linear regression analysis is made in order to predict total hemoglobin concentration. The correlation coefficient is 0.804 and the standard deviation is 0.864 g/dL for the calibration set. The relative percent error and standard deviation of the prediction set are 8.5% and 1.142 g/dL, respectively. We successfully demonstrate the possibility of noninvasive hemoglobin measurement, particularly, using the wavelengths below 1000 nm.     

Importance of using soluble derivatives in assessing bilirubin interference: the example of gamma-glutamyltransferase

In assessing possible in vitro interference from bilirubin on analytical methods, different results are to be expected from using either unconjugated (uB) or conjugated (cB) bilirubin as test materials, because of their different solubilities. In vitro interference of a synthetic soluble bilirubin derivative (ditauro-bilirubin, dtB) on gamma-glutamyltransferase activity measurement has been studied, in comparison with uB. In three out of five analytical methods/systems for the measurement of the enzyme activity, significantly higher (negative) interference was observed in the presence of the soluble derivative. Whichever the mechanism for the observed effect, the opportuneness of using soluble derivatives in order to assess bilirubin interference is pointed out: pathological serum specimens, submitted for laboratory investigations, are indeed frequently loaded with soluble bilirubin conjugates.     

Drug interference with measurement of metanephrines in urine

The influence of 35 commonly used drugs on measurement of metanephrines in urine was evaluated. Two concentrations of drugs were chosen for study based on usual doses and the percent of dose excreted unchanged in the urine. At "medium" drug concentrations, only phenylephrine falsely elevated metanephrine levels, whereas at a 10-fold higher drug concentration, guanethidine, hydrocortisone, imipramine, isoetharine, levodopa, phenobarbital, and phenylephrine caused positive interference. Propranolol and theophylline caused a negative interference at the two concentrations studied. The significance of these results is discussed.     

The measurement of fractionated bilirubin by Ektachem film slides. Method validation and comparison of conjugated bilirubin measurements with direct bilirubin in obstructive and hepatocellular jaundice

The authors evaluated the Kodak Ektachem Slides for total, "direct," conjugated, unconjugated, and albumin-bound ("delta") bilirubin. For various concentrations of control material, the precision (CV) within- and between-day ranged from 1.7 to 2.4% (2.8-6.6%) for total bilirubin, 0.8-4.2% (1.6-11.5%) for unconjugated bilirubin, and 1.6-9.5% (2.6-20.7%) for conjugated bilirubin. The Ektachem total and "direct" bilirubin assays demonstrated excellent correlation with the Jendrassik and Grof procedure; a 30% difference was observed, however, between absolute numbers with the two direct bilirubin methods. We found the measurement of true conjugated bilirubin by the Kodak Method to be superior to the measurement of "direct" bilirubin in following the response to treatment of various hepatic disorders manifested by extrahepatic and intrahepatic biliary obstruction.     

Calibrated automated thrombin generation measurement in clotting plasma

Calibrated automated thrombography displays the concentration of thrombin in clotting plasma with or without platelets (platelet-rich plasma/platelet-poor plasma, PRP/PPP) in up to 48 samples by monitoring the splitting of a fluorogenic substrate and comparing it to a constant known thrombin activity in a parallel, non-clotting sample. Thus, the non-linearity of the reaction rate with thrombin concentration is compensated for, and adding an excess of substrate can be avoided. Standard conditions were established at which acceptable experimental variation accompanies sensitivity to pathological changes. The coefficients of variation of the surface under the curve (endogenous thrombin potential) are: within experiment approximately 3%; intra-individual: <5% in PPP, <8% in PRP; interindividual 15% in PPP and 19% in PRP. In PPP, calibrated automated thrombography shows all clotting factor deficiencies (except factor XIII) and the effect of all anticoagulants [AVK, heparin(-likes), direct inhibitors]. In PRP, it is diminished in von Willebrand's disease, but it also shows the effect of platelet inhibitors (e.g. aspirin and abciximab). Addition of activated protein C (APC) or thrombomodulin inhibits thrombin generation and reflects disorders of the APC system (congenital and acquired resistance, deficiencies and lupus antibodies) independent of concomitant inhibition of the procoagulant pathway as for example by anticoagulants.     

An automated method for the measurement of folate activity

A new approach to the estimation of folate activity is described. The system may be used as a semi-automated method or as a fully automated method using the AutoAnalyzer or Mecolab equipment. The methods use a chloramphenicol-resistant strain of L. casei as the test organism, and this eliminates the need for sterilization or aseptic addition. The systems are able to handle extremely large numbers of samples in a relatively short time. Results are similar to those obtained by standard techniques.     

Toward the automated measurement of the Type-A behavior pattern

Sixty-six structured interviews that were rated by Rosenman on a 5-point Type A/B behavior pattern scale, were scored by means of a semiautomated system for verbosity, voice volume and the temporal pacing of speech. A significant negative correlation obtained between interviewees' A/B ratings and their reaction-time scores; significant positive correlations obtained between their behavior type ratings and their voice volume and duration of vocalization scores. A regression equation consisting of reaction-time and voice volume scores correctly classified the A/B ratings of 89 percent of the interviewees. The significant correlations that were obtained between the interviewer's and the interviewees' speech patterns emphasize the need for standardizing the interviewer's style. Finally, the findings suggest that anxiety-arousal is a mediating variable in the relationship between Type-A behavior and coronary heart disease.This paper is based on a Master's thesis conducted by the first author under the supervision of the second author.     

An automated biochemical assay for haptoglobin: Prevention of interference from albumin

Measurement of the acute phase serum protein, haptoglobin (Hp), is performed by biochemical methods based on haemoglobin binding, in many veterinary diagnostic laboratories. During attempts to develop a robust biochemical assay for serum Hp it was discovered that serum albumin interfered with the assay system increasing results by as much as 0.28 mg/ml, which could affect interpretation of results especially in species with low normal Hp concentrations. A reagent cocktail (SB-7) was devised which inhibited the interfering effect of albumin. An automated assay for Hp utilising SB-7 was developed for production as a biochemical assay kit and was evaluated for use in veterinary diagnosis. The intra-assay coefficients of variation were of 0.9%, 0.9% and 1.3% for Hp concentrations of 2.0, 1.0 and 0.23 mg/ml, respectively and interassay coefficients of variation of 1.7% and 4.5% for Hp of 2.08 mg/ml and 0.24 mg/ml, respectively. The lower limit of detection of was 0.02 mg/ml, linearity extended to 8 mg/ml and recovery was 101±7% (mean ±SD). The assay had correlation coefficients (R²) of 0.96 and 0.90 when compared with immunodiffusion assays of canine Hp and bovine Hp, respectively. Lipaemia and bilirubinaemia caused no interference. Haemolysis did not affect measurement of low levels of Hp, but at serum Hp concentrations of 0.4 and 1.8 mg/ml the apparent Hp concentration was decreased. Elevated concentrations of Hp were measured in cattle with mastitis, dogs with polyarthritis and rats experimentally infected withBordetella pertussis. The automated assay is precise and has negligible interference from albumin.     

Spurious hemoglobin Barts caused by bilirubin: a common interference mimicking an uncommon hemoglobinopathy

High-performance liquid chromatography (HPLC) is replacing electrophoresis for identification of hemoglobin variants. Our objective was to identify unknown tall peaks with elution times and shapes of hemoglobin Barts found on hemoglobin chromatograms that could not be confirmed by alkaline and acid gel electrophoresis. Of 90 specimens identified with this peak, 86 were from patients with hemoglobin SS. Regression of the height of the unknown peaks to serum bilirubin concentrations, diminution of the unknown peaks by washing the specimens, and chromatographic similarity of a total bilirubin serum calibrator, a bilirubin proficiency testing specimen, and 3 patients' serum samples with markedly elevated bilirubin to hemoglobin Barts provide evidence the peak was bilirubin. We suggest exclusion of bilirubin before HPLC results are reported as consistent with hemoglobin Barts.