Search

The Stratus total triiodothyronine (T3) immunoassay is an automated fluorometric enzyme immunoassay that utilizes a mouse monoclonal anti-T3 antibody preimmobilized onto glass fiber paper. The rate of formation of the enzyme product, as measured by front surface fluorometry, is inversely proportional to Total T3 concentration in the sample. The authors evaluated this method with respect to precision, sensitivity, interfering factors, and correlation with a radioimmunoassay. The overall, between-run, and within-run precision of the assay measured at three concentration levels for a total of 60 determinations each using immunoassay control materials, ranged from 2.5% to 14.3%. A total of 200 specimens, including 40 classified as hyperthyroid, and 38 classified as hypothyroid were analyzed in duplicate by the Stratus (STR) system and by a commercially available radioimmunoassay method. The coefficient of correlation obtained was 0.97. Icteric, hemolyzed, azotemic, and lipemic samples were included in the comparison and do not appear to have any interfering effect on the assay. The range of the assay is from 0.8 to 12 nmol/L. In summary, the Stratus Total T3 immunoassay offers the advantages of sensitivity, specificity, and automation with a throughput rate of 45 samples/h.

The "high-performance" liquid-chromatographic method we report for measuring palmitate derived from saturated phospholipids in amniotic fluid is sensitive and precise and possesses a wide dynamic range. Palmitate from nonsurfactant sources is largely excluded. The procedure involves oxidation of the chloroform/methanol-extracted lipids with osmium tetroxide, precipitation of the resulting phosphatides with cold acetone, mild alkaline hydrolysis, derivatization of the liberated fatty acids to phenacyl esters, and reversed-phase chromatography. The method is no less convenient or more time-consuming than measurement of the lecithin/sphingomyelin ratio by thin-layer chromatography. The clinical usefulness of the procedure is indicated by results of a correlative study of 26 amniotic fluids evaluated by "lung profile" tests in a second laboratory. A value for dipalmitoyl lecithin of 13 mg/L or greater indicates fetal lung maturity.

The interference of atypical creatine kinase (CK; EC 2.7.3.2) with anion-exchange methods for the measurement of the CK-MB isoenzyme is now firmly established. False-positive results from this source are much more common than interferences caused by the BB isoenzyme. Atypical CK, at least in some patients, does not appear to be a genetic variant, nor could we relate it to a specific clinical diagnosis, to hypoxia, or to administration of a particular drug. Its behavior in an immuno-inhibition test for CK-B subunit indicates an immunological difference from the normal M subunit. Thus the change in immunological properties is associated with the altered electrophoretic properties. The variability of electrophoretic patterns suggests that atypical CK may represent multiple forms of creatine kinase rather than a unique entity.

We use an ion-exchange column-chromatographic technique for separating creatine kinase isoenzymes in serum, and occasionally observe what appears to be sustained increase in the MB fraction. Most patients whose sera show such behavior have myocardial disease, but not necessarily a recent myocardial infarction. Electrophoretic analysis of a small sampling of such sera revealed that the apparent MB migrates atypically, appearing distinctly between isoezymes MB and MM. In another electrophoretic system, the peak might easily be mistaken for MM. This unusual isoenzyme does not appear to be "macro" creatine kinase. In laboratories that use the ion-exchange technique, the possibility of a falsely positive MB value should be considered in subjects who show persistent increases together with normal or nearly normal values for total creatine kinase activity. A suitable electrophoretic method that clearly demonstrates this unusual isoenzyme should be used in such cases, for confirmation.

An enzymic rate method for measuring beta-hydroxybutyrate in plasma by use of beta-hydroxybutyrate dehydrogenase (EC 1.1.1.30) was adapted to the Roche COBAS-BIO centrifugal analyzer. Optimum reagent composition and reaction conditions were determined, to provide increased sensitivity and accuracy. Use of magnesium ions increased sensitivity. Comparison of results with those of a manual enzymic endpoint method involving perchloric acid protein-free filtrates of whole blood showed excellent correlation (r = 0.996). The method has good within-run and day-to-day precision. Linearity of the standard curve extends to 5000 mumol of beta-hydroxybutyrate per liter. The assay can be completed in less than 5 min and requires 15 microL of plasma and minimal reagent volumes.