Clinical chemistry
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To monitor changes in the concentration of blood lactate during physical exercise, we used an automated lactate analyzer based on an electro-enzymatic method with continuous blood sampling through a catheter. The lactate concentration was measured every 2 min; between measurements, the instrument was calibrated with a lactate standard. Ascorbic acid, bilirubin, hemoglobin, creatinine, uric acid, and glucose did not interfere with the measurements. ⋯ We measured the blood lactate concentrations in nine apparently healthy volunteers during exercise on a treadmill with an increasing workload. The point at which lactate concentrations started to increase was detected easily. Thus, the lactate analyzer is suitable for monitoring changes in blood lactate concentrations during exercise.
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We determined the millimolar absorptivities of the four clinically relevant derivatives of fetal and adult human hemoglobin in the visible and near-infrared spectral range (450-1000 nm). As expected, spectral absorption curves of similar shape were found, but the small differences between fetal and adult hemoglobin absorptivity were important enough that they should be taken into account in multicomponent analysis of hemoglobin derivatives. Common pulse oximeters, however, involving light of 660 and 940 nm, are so insensitive to the presence of fetal hemoglobin that they can be used safely in neonates. The error in pulse oximetry caused by the presence of carboxyhemoglobin is insubstantial, but methemoglobin gives either an understimation or an overestimation at high or low oxygen saturation, respectively, the turning point being near 70% saturation.
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A simple, sensitive method for estimating carbon monoxide in plasma is described. In this method, the carbon monoxide in plasma is trapped with hemoglobin and subsequently estimated by dithionite reduction. The method has an intra- and interassay precision (CV) of 10.7% and 12.8%, respectively, at a concentration of 1.12 mg of carbon monoxide per liter and has a detection limit of 0.1 mg/L. The reference interval for carbon monoxide in plasma from 17 men and eight women ranged from 0.14 to 0.60 mg/L (mean 0.36 mg/L).
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We used quantitative assays to measure the activity of the bone, liver, and intestinal forms of alkaline phosphatase in plasma in 75 patients with endstage chronic renal failure undergoing hemodialysis. The results were correlated with radiological and other biochemical indices of bone disease and with biochemical indices of liver disease. The total activity of alkaline phosphatase in plasma increased in 28 patients. ⋯ Osteocalcin and bone alkaline phosphatase, but not parathyrin, decreased with age, implying that the skeletal response to parathyrin may be age dependent. In patients with increased total alkaline phosphatase undergoing hemodialysis, the concurrent measurement of gamma-glutamyltransferase may help identify whether the enzyme increase originates from the liver or bone, but this approach wrongly identified the source of the increase in three of 28 patients. Therefore, we recommend a separate measurement of the bone isoenzyme of alkaline phosphatase.
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This report examines logical but not yet widely recognized ramifications of the Clinical Laboratory Improvement Amendments of 1988 (CLIA'88), federal legislation that will require certification of all laboratories examining human specimens. Examination of the CLIA'88 committee reports and committee hearings suggest that more than the conventional approach to laboratory standards will be needed to meet the public's expectations as articulated by our elected representatives. The conventional approach to clinical testing standards seeks to assure quality by regulating the laboratory analytical process. ⋯ We suggest that now is the appropriate time for laboratory professionals, practicing physicians, and the public to abandon conventional thinking regarding clinical laboratory standards. We believe that CLIA'88 reflects a shift in public expectations toward fail-safe laboratory testing and the need for additional government oversight in laboratory test quality. If these new expectations persist, CLIA'88 represents a potential landmark in the course of federal authority and the practice of medicine in the United States.