Clinical performance of an in-line point-of-care monitor in neonates.

OBJECTIVE: To evaluate the bias, precision, and blood loss characteristics of an ex vivo in-line point-of-care testing blood gas and electrolyte monitor designed for use in critically ill newborn infants. STUDY DESIGN: Study participants included consecutive neonates with an umbilical artery catheter (UAC) in use for clinical laboratory testing. The in-line monitor (VIA LVM Blood Gas and Chemistry Monitoring System, VIA Medical, San Diego, CA) was directly connected to the participant's UAC and the monitor's determinations of pH, PCO(2), PO(2), sodium, potassium, and hematocrit (Hct) were compared with those simultaneously drawn and measured with a standard bench top laboratory instrument (Radiometer 625 ABL; Radiometer America, Inc, Westlake, OH). The bias (the mean difference from the reference method) and precision (1 standard deviation of the mean difference) performance criteria of the in-line monitor were derived using standard laboratory procedures. RESULTS: Sixteen neonates monitored for a total of 37 days had a total of 229 paired blood samples available for comparison by the 2 methods. Bias and precision performance characteristics of the in-line monitor were similar to reports of other point-of-care devices (ie, pH: -.003 +/-.024; PCO(2):.35 +/- 2.84 mm Hg; PO(2):.39 +/- 7.30 mm Hg; sodium:.52 +/- 2.34 mmol/L; potassium:.17 +/-.18 mmol/L; and Hct:.61 +/- 2.80%). The range of values observed for each parameter included much of the range anticipated among critically ill neonates (ie, pH: 7.15-7.65; PCO(2): 25-75 mm Hg; PO(2): 25-275 mm Hg; sodium: 127-150 mmol/L; potassium: 2.6-5.5 mmol/L; and Hct: 32%-60%). Mean blood loss (+/- standard deviation) per sample with the in-line monitor was approximately one-tenth that of the reference method: 24 +/- 7 microL versus 250 microL, respectively. There was no evidence of hemolysis and no patient related safety issues were identified with use of the in-line monitor. CONCLUSIONS: Repeated laboratory testing of critically ill neonates using an ex vivo in-line monitor designed for use in neonates provides reliable laboratory results. The blood loss and hemolysis data obtained suggests that this monitoring device offers potential for reducing neonatal blood loss-and possibly transfusion needs-during the first weeks of life. Before this promising technology can be routinely recommended for care of critically ill neonates, greater practical experience in a variety of clinical settings is needed.

Cardiac troponin I levels are normal or minimally elevated after transthoracic cardioversion.

OBJECTIVES: The present study was designed to assess the impact of direct current shocks on cardiac troponin I (cTnI), which has greater sensitivity and specificity than creatine kinase (CK) for the diagnosis of myocardial injury. BACKGROUND: Transthoracic direct current shocks can cause myocardial injury. They also cause elevations of total CK and CK-MB fraction (CK-MB). METHODS: We obtained measurements of cTnI total CK and CK-MB before and after elective cardioversions in 38 patients. Blood samples were drawn before and 8, 16, 24 and 48 h after cardioversion. Shock energy, current, impedance and number of shocks delivered were tabulated. RESULTS: Patients received a mean (+/-SD) of 2.1 +/- 1.2 shocks with a median cumulative energy of 300 J (range 50 to 1,580). Three patients had minimal elevations (1.5, 1.2 and 0.8 ng/ml, normal < or = 0.6 ng/ml) of cTnI. Two of these patients had impaired left ventricular contractility by echocardiography. Thirty-five of the 38 patients had no elevations of cTnI. Sixty-two percent of patients had an increase in CK after cardioversion, but CK-MB was elevated to an abnormal level of 12.7 ng/ml (normal < 6.7) in only one patient after cardioversion. CONCLUSIONS: Cardiac troponin I levels are either normal or minimally elevated after elective direct current cardioversion, suggesting that subtle myocardial injury can be caused by direct current transthoracic shocks. However, substantial elevations of cTnI after cardioversion suggest the presence of myocardial injury from causes unrelated to the direct current shocks administered for cardioversion.

Genetic variants of serum albumin in Americans and Japanese.

A collaborative search for albumin genetic variants (alloalbumins) was undertaken by cellulose acetate and agarose electrophoresis at pH 8.6 of the sera of patients at two major medical centers in the United States and of nearly 20,000 blood donors in Japan. Seventeen instances of alloalbuminemia were ascertained, and seven different alloalbumin types were characterized by structural study. Two previously unreported alloalbumin types were identified. In one type, which was present in a Caucasian family and designated Iowa City-1, aspartic acid at position 365 was replaced by valine (365 Asp----Val); this is the second reported mutation at this position. The other type present in a Japanese blood donor had the mutation 128 His----Arg. An unexpected finding was the presence in a single Japanese of a Naskapi-type alloalbumin (372 Lys----Glu), a variant that had previously been described only for certain Amerindian tribes in whom it occurs with a polymorphic frequency (greater than 1%) and in Eti Turks. An arginyl-albumin (-1 Arg, 1 Asp----Val) occurred in an American family. The other alloalbumin types identified were proalbumins Lille and Christchurch and albumin B that have a cumulative frequency of about 1:3500 in Caucasians probably because of the hypermutability of CpG dinucleotides at the mutated sites. All of the variants characterized in this study are point mutants, and the sites are spread throughout the albumin gene. However, about one-fourth of all known albumin mutations are clustered in the sequence segment from position 354 through 382.

Kinetic measurement of bicarbonate in serum by thiocyanate inhibition of wheat germ phosphoenolpyruvate carboxylase.

We describe a kinetic enzymic method for serum bicarbonate analysis, using wheat germ phosphoenolpyruvate carboxylase (EC 4.1.1.31) coupled through oxaloacetate reduction with NADH in the presence of malate dehydrogenase (EC 1.1.1.37). Inhibition with potassium thiocyanate yielded first-order kinetics with respect to bicarbonate over the concentration range of 0-45 mmol/L. The inhibitor was chosen by evaluating reaction data in the presence of different anions, with use of a monoexponential model. Criteria for first-order kinetics included a constant reaction half-life over the concentration range and SDest for the model comparable with the magnitude of spectrophotometric noise. We compared our kinetic method (y) with an automated ion-selective electrode method (x), obtaining the regression relationship y = 0.97x + 1.2 mmol/L (r = 0.991; n = 77; mean = 25.5 mmol/L; y = 25.3 mmol/L). Within-run precision from duplicates was 3.1% (mean = 25.2 mmol/L; n = 72). Total analytical precision (n = 12) was 9.4% (mean = 15 mmol/L) for the low control and 4.3% (mean = 32 mmol/L) for the high control. We conclude that the kinetic assay allows use of large serum-to-reagent ratios (1:100) and smaller amounts of NADH than an equilibrium assay. The assay is suitable for automated kinetic analysis.

Multipoint kinetic method for simultaneously measuring the combined concentrations of acetoacetate-beta-hydroxybutyrate and lactate-pyruvate.

This is a multipoint kinetic method for simultaneously determining acetoacetate (AcAc) plus beta-hydroxybutyrate and lactate plus pyruvate in a single cuvette of the Multistat III centrifugal analyzer. In the first step, AcAc and pyruvate are completely reduced, using 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) and lactate dehydrogenase (EC 1.1.1.27) in the presence of excess NADH at pH 7.5, to beta-hydroxybutyrate and lactate, respectively. After dilution, the endogenous beta-hydroxybutyrate and lactate and that resulting from reduction are simultaneously oxidized by their respective dehydrogenases in the presence of excess NAD+ at pH 9.0. Adjustment of the relative enzyme concentrations allows simultaneous estimation of AcAc plus beta-hydroxybutyrate and lactate plus pyruvate by analyzing multipoint absorbance data, collected during the oxidation reaction, with use of a two-component linear-regression model. Total run-to-run CVs were 6.4% and 6.1% at 5 mmol/L beta-hydroxybutyrate and 5 mmol/L lactate, respectively. The method was designed to be useful for identifying the cause of an increased anion gap in serum.

Heterozygosity of alpha 1-antitrypsin: a health risk?

alpha 1-Antitrypsin is a serum glycoprotein synthesized in the liver. It consists of a single polypeptide chain with a molecular weight of about 52,000. The molecule exhibits great genetic diversity with multiple codominant alleles at a single autosomal locus. The majority of the population expresses the M allele. The Z allele, which is the result of a single amino acid substitution, results in levels of alpha 1-antitrypsin that are only 10 to 15% of normal when inherited in the homozygous state. Two main pathological consequences of this state are liver and lung disease. The homozygous S phenotype has also been associated with reduced alpha 1-antitrypsin levels and pathology. The homozygous Z phenotype has an incidence of about 1 in 1700 in certain European populations. People who are heterozygous for the S or Z allele usually have alpha 1-antitrypsin levels which are about 60% of normal. The combined frequency of these alleles in the population may reach 10 to 15%. This review examines the controversy as to whether these individuals are at increased risk for pathology due to their reduced alpha 1-antitrypsin levels.

Kinetic measurement of the combined concentrations of acetoacetate and beta-hydroxybutyrate in serum.

This is an automated method for the kinetic measurement of the combined concentrations of acetoacetate and beta-hydroxybutyrate in a single channel of the "Multistat III" centrifugal analyzer. Acetoacetate is first reduced with high concentrations of NADH by catalysis with 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30). This reaction mixture is diluted with excess NAD+. The endogenous beta-hydroxybutyrate and that resulting from acetoacetate are then measured kinetically. Comparing the combined concentration of acetoacetate and beta-hydroxybutyrate (y) with the sum of acetoacetate and beta-hydroxybutyrate measured as described by Hansen and Freier (Clin Chem 1978;24:475) (x) yielded the relationship: y = 0.99x - 0.57 (r = 0.93, n = 25). The run-to-run CVs for low (5 mmol/L) and high (15 mmol/L) acetoacetate controls were 12% and 6%, respectively. The method is useful for determining the concentration of ketone bodies in 2-microL samples of serum of patients with diabetic ketoacidosis. The sensitivity can be increased to determine ketone body concentration in nonketotic individuals by increasing sample volume to 10 microL.

Cystinuria.

Cystinuria is an inherited metabolic disease resulting in renal stone formation. An incidence of 1 in 7000 makes it a relatively common genetic disease. The biochemical defect is a carrier protein in the epithelial cells of certain organs. This carrier protein is responsible for the transport of cystine and the dibasic amino acids. Cystine is a poorly soluble compound which precipitates in acid urine and results in renal calculi. Cystine stones account for 1 to 2% of all renal calculi. Homozygotes are detected by the high concentration of cystine in their urine. Treatment consists of sulfhydryl compounds that form more soluble compounds with cystine through sulfhydryl exchange as well as alkalinization of urine and hydration to make cystine more soluble.

Quantification of analyte and interferent by multipoint analysis.

We have investigated the application of multipoint kinetic curve-fitting methods to the determination of an analyte in the presence of a single interferent. Our model system for the analyte-interferent was creatinine-acetoacetate as determined with the kinetic Jaffé method. We examined the utility of the following multipoint approaches: simultaneous equations, multivariable linear regression, and iterative multivariable nonlinear regression. With appropriate restrictions, all approaches could detect acetoacetate interference and quantify both creatinine and acetoacetate. A two-stage linear regression approach was both versatile and computationally simple. Interferent was detected in the first stage, and both analyte and interferent were quantified in the second stage if the interferent was assumed known and an adequate fit of the model to the data was obtained. Using the two-stage linear regression model, we obtained results for 10 ketotic patients that correlated well with results by enzymatic methods for creatinine (r = 0.976) and acetoacetate (r = 0.995); we also demonstrated that creatinine could be quantified in the presence of the antibiotic cefoxitin.

Probably myocardial infarction in a 14-year-old boy.

After vigorous physical activity a 14-year-old boy from a family with a strong history of cardiac disease developed symptoms consistent with a myocardial infarction, a relatively rare event in this age group. Isoenzyme patterns of creatine kinase and lactate dehydrogenase were consistent with the occurrence of an infarction.

Hematological Variations After Endurance Running With Hard-and Soft-Soled Running Shoes.

In brief: Blood measurements were taken in 23 marathon runners to investigate whether the hardness of the sole of the running shoe would affect RBC indexes. Runners were randomly assigned to a group with either a firm-sole running shoe or an air-cushion shoe. Measurements before and after the 15-mile run included complete blood count, serum haptoglobin, plasma hemoglobin, and venous hemoglobin. Runners wearing air-cushion shoes demonstrated smaller hematological effects after strenuous exercise than did runners wearing firm-sole shoes. This study indicates that (1) material property of the running shoes may be correlated with physiological measurements, and (2) appropriate cushioning in running shoes may reduce the RBC abnormalities experienced in long-distance running.

Centrifugal analysis for serum iron and iron-binding capacity using the IL Multistat III Analyzer.

A colorimetric method for the determination of serum iron and total iron-binding capacity (TIBC) has been adapted to an IL Multistat III Centrifugal Analyzer. The correlation to an ESA Ferrochem, Model 3050, which measures iron by coulometry, is acceptable (IL Multistat = 1.08 ESA--5.05). The intra-run precision gave an average C.V. of less than 5%. The day-to-day precision was between 2% and 7% and the average analytical recovery was 102%. This method requires only 150 microliters of sample for both iron and TIBC which is a significant advantage over many existing methods in terms of sample volume, especially when a pediatric population is considered. Both iron and TIBC may be analyzed at the same time on the same rotor. The approximate analysis time is 30 minutes for seven iron and TIBC samples, four controls and one standard. The cost is low, being approximately $0.08 per iron assay and $0.83 per TIBC assay.

Single-stage automated assay for heparin.

We have developed a single-stage assay for heparin, using reagents modified from the two-stage Dade Protopath heparin synthetic substrate assay. The single-stage assay involves simultaneous mixing of a plasma sample, an antithrombin III source, alpha-thrombin, and the alpha-thrombin fluorogenic substrate. The synthetic substrate, antithrombin III, and heparin-antithrombin III complex compete for the alpha-thrombin active site. The alpha-thrombin is inactivated by the heparin-antithrombin complex while substrate is being hydrolyzed, so that total product formation decreases with heparin concentration. Day-to-day CV was 9.3% at a heparin concentration of 246 USP units/L. Comparison of results of the single-stage heparin assay with those of a two-stage esterolytic assay yielded the linear regression equation: esterolytic = 0.834 (single-stage)--7 USP units/L (r = 0.94, n = 47). Bilirubin interfered with the single-stage assay, resulting in an apparent increase in sample heparin concentration. The single-stage heparin assay can be automated for centrifugal analyzers capable of double-reagent addition and fluorometric detection, substantially decreasing reagent requirements and therefore costs.

An enzymic, reaction-rate assay for serum creatinine with a centrifugal analyzer.

We describe a procedure for specific, rapid, kinetic determination of creatinine, in which a manual coupled-enzyme micro-scale assay is adapted to a centrifugal analyzer. The creatinine reaction is ultimately linked to NADH utilization, which is measured by the absorbance change at 340 nm. This procedure requires 15 microL of serum and the standard curve is linear to a creatinine concentration of 200 mg/L. A four-point kinetic algorithm allows the dynamic range of the assay to be extended without sacrificing sensitivity, and makes a separate serum blank unnecessary. The within-run precision (CV) for samples with a creatinine concentration of 11 and 52 mg/L was 5.6 and 2.4%, respectively; day-to-day CV for a creatinine concentration of 11 mg/L was 7.7% (n = 21). We compared this procedure with a kinetic Jaffé procedure, with excellent agreement (r = 0.996; y = 0.96x + 2.4 mg/L). Bilirubin, non-esterified fatty acids, and ketone bodies do not affect creatinine determinations by this method; thus the method is especially useful for monitoring the renal function of diabetics.

Use of alpha cyclodextrin to eliminate interference by nonesterified fatty acids in calcium measurements.

This study shows that nonesterified fatty acids cause underestimation of serum calcium by some colorimetric methods. The underestimation of calcium occurs infrequently, but can be as large as 20-30 mg/l. Preincubation of the sample with alpha cyclodextrin will eliminate this interference. The procedure is simple, inexpensive, and applicable to most clinical laboratories.

Esterolytic method for determination of heparin in plasma.

This assay for heparin is based on the heparin-accelerated rate of alpha-thrombin III. The rate or product formation from the residual active thrombin is inversely proportional to plasma heparin content. The assay can be performed manually, but our results were obtained with a discrete analyzer, the ABA-100. The assay is insensitive to concentrations of antithrombin III in plasma. Precision studies gave CVs of less than 10%. This assay was compared to the Dade Protopath heparin assay and a correlation coefficient of 0.90 was obtained (n = 62). The correlation between activated partial thromboplastin times and heparin concentrations (r = 0.67) was calculated frm results on 78 plasma specimens from 10 patients.