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Four enzymatic methods for creatinine measurement were evaluated on a DuPont Dimension automatic analyzer. Biomed Creatinine-Duo-UV (BIO) and Raichem Creatinine Reagent Enzymatic (RAI) start creatinine breakdown with creatinine iminohydrolase (EC 3.5.4.21) resulting in the formation of NH4+. The Boehringer Mannheim Creatinine PAP (BM1) and SopaChem Creatinine (SOP) start the breakdown of creatinine with creatininase (EC 3.5.2.10) which yields creatine. In order to reduce bilirubin interference, the BM1 method was modified to contain K4Fe(CN)6. This substance was added with reagent 1 (BM2) or with reagent 2 (BM3). All the enzymatic creatinine methods tested displayed good linearity for concentrations up to at least 1000 mumol/l. The BIO, BM3, RAI and SOP methods showed good stability of test outcome for the tested period of a week. The outcome of the BM1 and BM2 method increased continually with time. Only the results of the RAI method were diminished by the presence of lipids. The BM1, BM2, BM3 and SOP methods showed no interference with haemoglobin, whereas this increased the outcome of the BIO method and slightly decreased the results of the RAI method. Using spiked human albumin solutions it was found that the BIO, BM2, BM3 and RAI methods displayed good resistance to interference by bilirubin or ditauro-bilirubin. The outcome of the BM1 and SOP method was strongly decreased by both bilirubin and ditauro-bilirubin. When creatinine was measured in a panel of sera originating from 100 patients with bilirubin concentrations higher than 50 mumol/l, the obtained results were in close agreement with those found for the spiked human albumin solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

The different matrix properties of neonatal serum and commercial control samples can lead to considerable errors in the calibration and control of bilirubinometers. These difficulties can be avoided by calibration with serum from healthy adults which is supplemented with unconjugated bilirubin. But this procedure is impracticable for most routine laboratories. Under certain preconditions, control samples, with bilirubin concentrations determined with correctly calibrated bilirubinometers or spectrophotometers, are also suitable as calibrators. This was established by determination of the bilirubin concentration of 16 different control samples, using both the reference method and correctly calibrated bilirubinometers or spectrophotometers in three or four specialist laboratories. This was also confirmed in several interlaboratory surveys, some involving up to 72 laboratories. The results of these investigations show that a control sample should be used for the calibration of a bilirubinometer only if it meets the following preconditions: 1. There should be no significant difference between the bilirubin values determined with the reference method and with a correctly calibrated spectrophotometer or bilirubinometer. 2. The bilirubin concentration should lie in the range 230-300 mumol/l. The photometric response of bilirubinometers has a limited linear range, so that analytical results greater than 300 mumol/l must be rated as basically unreliable.

A study is reported on the determination of creatinine with the DuPont Dimension, paying special attention to interference by bilirubin. Various methods for dealing with bilirubin interference are described, including modification of the Jaffé reaction, enzymatic assay of creatinine, enzymatic destruction of bilirubin, and ultrafiltration of the serum sample. None of these modifications gave completely satisfactory results, although the Jaffé method with a ferricyanide oxidation step, and the enzymatic assay with ferrocyanide gave reasonable results with icteric specimens from adult patients, while only the latter method could be used for neonatal serum samples.

A study was undertaken to evaluate the accuracy of the Reflotron creatinine determination. Two aspects are reported: the calibration of the instrument and the influence of bilirubin on the test result. As the reference method, an HPLC based technique was used. Variations due to the instrument as well as to the test strip were found, while interference by bilirubin proved to be very moderate.

An HPLC-based method for the determination of creatinine was evaluated, with emphasis on interference by bilirubin. The method differed from other procedures, in that deproteinization was by ultrafiltration instead of precipitation with trichloroacetic acid. This allows a rapid, direct analysis by HPLC with very few experimental steps. Analytical results showed linearity up to 5000 mumol/l and an average analytical recovery of 100%. Within-day imprecision was 0.8-1.4%, and day-to-day imprecision was 0.5-2.4%.

A new promising treatment for patients with symptomatic cholelithiasis is extracorporeal shock wave lithotripsy. In order to learn how to interpret the computed tomographic (CT) densities of gallstones measured in vivo, our radiologists asked the clinical chemistry laboratory to analyse cholesterol, bilirubin and calcium in gallstones. No reference methods for the analysis of gallstones have been described. A literature search for manageable quantitative methods for these analyses was not successful. Among the different X-ray diffraction, infrared and chemical analyses described, we could find no well documented analyses that have been compared with reference methods or proposed reference methods for serum. This finding prompted us to develop chemical methods for cholesterol, bilirubin and total calcium in gallstones starting from (proposed) reference methods for serum and to investigate the accuracy, imprecision and linearity of these methods.

A study is described on the standardization of the determination of neonatal total bilirubin. A wide variation in results was shown in surveys held in The Netherlands and Germany and the reasons for this variation were sought. The suitability of commercial bilirubin standards and direct reading instruments, widely used in the neonatal field, was tested by comparing all measurements with those obtained with the candidate reference method. We found differences between the stated values and those obtained by the reference method. However, a bias was also shown to exist between the results measured with the direct reading instruments and those obtained with the reference method, explaining at least qualitatively, the variation seen in the surveys. In addition, problems in the calibration of the DuPont ACA are discussed.

Experience in surveying the neonatal bilirubin determination in the Netherlands is described. Initially it was organized as a local activity (the Rotterdam area), then later enlarged to a national scale (some 150 participants). A number of items is discussed i.e. the initial improvements, which stabilized at an interlaboratory imprecision of about 8%, and further changes that could improve this rather high imprecision.

A spectrometric modification of the determination of total bilirubin with the Du Pont ACA is described. Accuracy, precision and standardization problems are discussed in comparison with the earlier published diazo modification, as well as other techniques well known in the field of neonatal chemistry.

Three surveys were organized in the Rotterdam area with respect to the determination of total bilirubin in neonatal sera. Fifteen hospital laboratories participated. The coefficients of variation dropped from about 15% (survey 1) to about 8% (survey 3). This improvement was reached by discussing the techniques used, and in some cases by changing them.

Certain problems in the standardization of direct-reading instruments (bilirubinometers) were investigated. It was shown that the combination of wavelength setting and choice of pH is very important with respect to the standard to be used. It is emphasized that in fact there is no synthetic bilirubin standard which can be used as primary standard. Reasons are given why the only pragmentic solution proved to be a pool of neonatal serum.

The interference of hemoglobin in the determination of total bilirubin with the Du Pont ACA was studied. The method seemed of limited value in our opinion especially with respect to neonatal sera. By changing the wave-length setting a rather broad plateau was found when the hemoglobin concentration was plotted against the actual bilirubin concentration. On the basis of these findings a new calibration graph was constructed and programmed into the ACA. The new method correlates well with two other micro bilirubin techniques.