Organic acids interfere in the measurement of carbon dioxide concentration by the Kodak Ektachem 700.

A significant discrepancy was noted in our laboratory between the total plasma carbon dioxide concentration measured by the Kodak Ektachem 700 and the bicarbonate concentration derived from the Corning 170 pH/Blood Gas analyser in an 8-day-old patient. The concentration of total carbon dioxide was 18 mmol/L while the derived bicarbonate was 13 mmol/L. The patient was eventually diagnosed as maple syrup urine disease. This finding led us to examine the effect of various organic acids on the measurement of carbon dioxide by the Ektachem 700. Several interfered significantly. Clinicians should be aware that when organic acid concentrations are increased, the Ektachem 700 total carbon dioxide result may be falsely raised.

A comparison of three desktop chemistry analyzers for the pediatric practice.

Three desktop chemistry analyzers most frequently utilized in physicians' offices are compared for performance and precision: the DT60 (Kodak), Vision (Abbott), and Reflotron (Boehringer-Mannheim). The manufacturers' instructions were followed for all the reagents, calibrators and controls provided with each analyzer used. Precision, stability, dynamic range, interferences, and comparison of analyses of 50-100 patient samples with standard laboratory instruments were evaluated. Within-run precision on all three instruments was acceptable, the coefficient of variation (% CV) ranging from 0.8-5.4% and run-to-run precision CV of 1.1-7.3%. Within-run precision for glucose, blood urea, nitrogen, cholesterol and sodium for an experienced technologist, a clerk without any laboratory experience and a physician with no recent laboratory training were compared: the total CV varied between 1.1 and 6.3%. There are differences in the way bilirubin and hemoglobin interfere with the chemistries on the analyzers. Instrument size, available analyses, reagent cost and ease of operation were also assessed. The data suggest that all three analyzers performed well and would be suitable for the pediatric office setting.

A dry-strip immunometric assay for digoxin on the Ames Seralyzer.

We evaluated the Ames Seralyzer III with a new reagent and drystrip test for assay of digoxin. Assay precision was acceptable in the therapeutic range. Within-run imprecision (coefficient of variation, n = 20) was 7% at 0.9 ng/ml (1.2 nM) and 3.5% at 1.9 ng/ml (2.4 nM); run-to-run imprecision was 7.6% at 0.8 ng/ml (1.0 nM) and 5.7% at 2.1 ng/ml (2.7 nM). The method is very reproducible and is linear between 0.5 and 4.3 ng/ml (0.6-5.5 nM). The assay performed well with patient samples, with Abbott TDx used as the reference procedure. Bilirubin up to 16 mg/dl (273 microM) and hemoglobin up to 11 g/l do not cause interference. Digoxin-like immunoreactive factors cause minimal interference. Some digoxin metabolites such as monodigitoxoside, bis-digitoxoside, and digoxigenin cross-react with the digoxin antibody. Patients on spironolactone have falsely increased digoxin values. The new digoxin assay is easy to perform and uses 30 microliters serum; the result can be reported in 15-20 min.

Another physician's office analyzer: the Abbott "Vision" evaluated.

We evaluated the Abbott Vision system, to assess its suitability for use in the physician's office setting. We compared results from Vision for all the available analytes (alkaline phosphatase, urea nitrogen, cholesterol, creatinine, glucose, uric acid, and triglycerides) with results from the Kodak Ektachem 400 and 700. For all analytes, standard curve linearity, assessed with various dilutions of an analyte-supplemented serum pool, was within the ranges claimed by the manufacturer. Within-run precision (CV) for assays of these analytes ranged from 0.9% to 4.7%, run-to-run precision from 1.1% to 7.3%. Comparisons with other methods were generally very good except for a bias in results for blood urea nitrogen and alkaline phosphatase. Hemolysis (hemoglobin at 2.0 and 3.0 g/L) interferes with results for cholesterol, glucose, triglycerides, and uric acid in serum and whole blood. Bilirubin at 82 mg/L interferes with results for creatinine and triglycerides; at 120 mg/L it interferes with cholesterol, glucose, and uric acid results; and at 170 mg/L it interferes with alkaline phosphatase results. Triglycerides up to 5000 mg/L do not interfere with any of the tests. Calibration of the analyzer was stable for one month. We also compared the performance of a skilled operator with that of an unskilled operator and a physician.

Hemoglobin, electrolytes, and other major clinical laboratory analytes as measured with a physician's office analyzer, the Kodak DT60.

We evaluated the Kodak DT60 analyzer, to assess its suitability for use in the physician's office setting. The DT60 Analyzer is based on the same multilayer film technology as used in the Ektachem 400 and 700. We compared results obtained with DT60 for all the analyses currently available for use in this instrument (Na+, K+, Cl-, glucose, urea nitrogen, uric acid, total bilirubin, total protein, amylase, cholesterol, and triglycerides) with results from a Kodak Ektachem 700 Analyzer and from other laboratory procedures. Results for hemoglobin were compared with those from a Coulter Counter Analyzer. For all analytes, linearity of the standard curve for various dilutions of Ektachem calibrators was within the manufacturer's claims. CVs for within-run precision ranged from 0.8% to 5.4%, run-to-run CVs ranged from 1.6% to 7.5%. Except for amylase, comparisons with other methods were generally very good. The only interference we observed was that of hemoglobin in the bilirubin assay. Calibration was stable for longer than one month. We also compared the performance of a skilled operator with that of an unskilled operator and of a physician.

Ektachem multilayer dry-film assay for ammonia evaluated.

We evaluated the Kodak Ektachem multilayer dry-film method for ammonia. Within-day precision (CV) was 5.9% and 2.7% at ammonia concentrations of 53 and 654 mumol/L, respectively. Between-run precision (CV) was 7.8% and 7.3% at 51 and 109 mumol/L, respectively. Correlation with a manual ion-exchange chromatography-Berthelot reaction-based method (x) was good (y = 0.96x - 1.37; r = 0.984; SEE = 9.16). The response of the method varies linearly with ammonia concentration up to 900 mumol/L. Bilirubin less than or equal to 270 mg/L, triglycerides less than or equal to 6.0 g/L, and slight hemolysis did not interfere. The concentration of ammonia in plasma of 120 healthy adults was 16-53 mumol/L (nonparametric central 95 percentiles).

Adolescent pregnancy testing: which test to use.

In order to study the sensitivity and efficiency of five pregnancy tests, we evaluated four types of urine tests in 162 adolescent girls in whom pregnancy was suspected; a serum test was performed in 46 of them. We found that (1) an increase in sensitivity occurred at the expense of specificity, (2) the quantitation of the beta-subunit of human chorionic gonadotropin in serum proved to be the most reliable test for pregnancy, and (3) the latex agglutination inhibition tube test (Placentex) was the most accurate of the four types of urine tests evaluated. We concluded that for adolescents, the serum pregnancy test is the preferred test, but when it is not available, the urine latex agglutination inhibition tube test offers the most reliable alternative.

Adaptation of the EMIT gentamicin and tobramycin procedure to the IL microcentrifugal analyzer.

We have adapted the Syva Emit gentamicin and tobramycin procedure to the IL microcentrifugal analyzer, MCA III. With this instrument the recommended instructions for reagent preparation and reaction sequence did not produce a useable standard curve. We modified the dilutions and volumes for the working reagents and reversed the sequence of addition of the working reagents. WE assessed the linearity and precision of the analysis and compared the Syva gentamicin and tobramycin Emit procedure on the IL MCA III with the semiautomated procedure on a Gilford Stasar III spectrophotometer. With the IL MCA III only 3 to 5 microliter of serum is used, 17 analyses can be obtained in 8 min, and the reagent costs are reduced considerably.

Reference values for cerebrospinal fluid glutamine concentration in infants.

We measured cerebrospinal fluid glutamine concentration in a reference group of 85 newborn to 30-month-old infants. All of the spinal taps were performed for the diagnosis of illnesses unrelated to hyperammonemia or hepatic encephalopathy. We also analyzed samples from patients with meningitis or cerebral hemorrhage, or who were receiving total parenteral nutrition. The mean glutamine concentration in cerebrospinal fluid in the reference group was somewhat lower than values reported for older children and adults. Values were significantly higher in patients with meningitis or cerebral hemorrhage and in those infants receiving total parenteral nutrition.

Monitoring pediatric serum theophylline, phenobarbital, and phenytoin with the IL Multistat III.

We compared results of theophylline, phenobarbital, and phenytoin assays by the EMIT method using the IL Multistat III Micro Centrifugal Analyzer with results by the EMIT semiautomated procedure on a Beckman 25 spectrophotometer equipped with a semiautomated pipettor-dilutor and a model 2400 automatic timer/printer. We assessed linearity, precision, specificity, and correlation with other methods, The IL MCA III is precise, easy to use, and suitable for routine use in a pediatric laboratory. Only 3 microliter of serum is used for each drug analysis, and 17 results can be obtained in 8 min. Reagent costs can be reduced fourfold.

Evaluation of the Beckman creatinine analyzer.

We compared results obtained with the Beckman Creatinine Analyzer (Beckman Instruments, Inc.) to those with the GEMSAEC Centrifugal Analyzer (Electro-Nucleonics, Inc.) and with a manual method for determination of creatinine in serum and urine. Linearity, stability, recovery, and precision were evaluated. Interference from bilirubin, protein, lipemia, uric acid, and hemolysis is negligible, but acetone and acetoacetate can interfere.

Limitations of immunochemical measurement of ceruloplasmin.

We describe a quantitative immunochemical method for the nephelometric measurement of ceruloplasmin. Results are compared with those from a radial immunodiffusion technique. We examine factors affecting the results, such as antiserum source and calibrators, and list reference limits for a pediatric population.

Chemical and immunochemical measurement of total iron-binding capacity compared.

Radiometric, colorimetric, and two immunochemical methods for measuring total iron-binding capacity are compared. We evaluated the procedures on the basis of precision, applicability to a pediatric population, and accuracy as assessed by analytical recovery of purified transferrin. The immunoephelometric assay for transferrin provides significant advantages over the other methods examined.

Kinetic measurement of alpha-amylase with a centrifugal analyzer.

We compared results of an enzymic assay for alpha-amylase (EC 3.2 1.1), adapted to a centrifugal analyzer (GEMSAEC), with results by the manual dyed-starch (Phadebas) amylase assay. We assessed linearity and precision, and the stability of the reagent. The kinetic procedure is rapid, precise, requires only 25 microliter of serum, and thus is evidently suited for both pediatric and emergency use.

An evaluation of the Beckman chloride/carbon dioxide analyzer.

We compared the Beckman Cl/CO2 Analyzer to the American Instrument Company chloride titrator for measurement of chloride in serum, sweat, and spinal fluid. We also compared it to the Natelson gasometer and a modified continuous-flow (AutoAnalyzer) technique for measurement of carbon dioxide in serum. Effects of bilirubin and hemoglobin on results for both the CO2, and Cl were negligible. The linearity, stability, and precision of the equipment was studied. We believe the Beckman Cl/CO2 Analyzer to be ideal for simultaneous measurement of chloride and carbon dioxide in a pediatric or emergency-determination setting.