Biomedical subjects
Publications and source records attributed to J I Heald.
Two methods for determining serum theophylline concentrations were compared against a standard laboratory assay. Each method was evaluated for ease of use, accuracy, and precision. Although both methods were found to be easy to use, there were major differences between the assays in both accuracy and precision.
We evaluated the analytical and clinical performance of three "sensitive" immunoradiometric assay (IRMA) kits (Tandem-R TSH HS, Hybritech, Inc.; EchoClonal TSH, Bio-Rad; Coat-A-Count TSH IRMA, Diagnostic Products Corp.) for measurement of thyrotropin (TSH) and compared their performance against a "regular" IRMA (ARIA-HT, Becton-Dickinson) to determine whether these assays might eliminate the need to perform the thyroliberin (TRF) stimulation test. We concluded that the Tandem and EchoClonal kits may obviate the need to perform TRF stimulation tests in some patients. Using only the basal TSH concentration to predict the TSH response to TRF, we found all three sensitive TSH assays to be useful for detecting abnormal thyrotroph function. Dose-response, linearity, analytical recovery, and specificity were acceptable for all kits, but intra-assay precision at very low TSH concentrations and analytical sensitivity differed considerably among the kits. Using the EchoClonal assay, we established a normal reference interval for TSH of 0.4-4.6 milli-int. units/L.
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We evaluated the analytical performance of the "SimulTROPIN" (Becton-Dickinson Inc.) radioimmunoassay for the simultaneous measurement of lutropin (LH) and follitropin (FSH) in human serum. Dose response, linearity, analytical recovery, sensitivity, and reagent stability were all acceptable. Cross reactivity with other structurally related hormones [choriogonadotropin (CG) and thyrotropin (TSH)] was minimal. A normal reference interval was established for nonmidcycle, ovulatory women. We confirm the low degree of CG and TSH cross reactivity with LH and FSH reported by Becton Dickinson and conclude that this assay is an acceptable method for laboratory use in the simultaneous quantification of these analytes.
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Two commercial methods, the API 20S system (API; Analytab Products, Inc., Plainview, N.Y.) and the Gram-Positive Identification Card (GPI; Vitek Systems, Inc., Hazelwood, Mo.), were evaluated without additional tests for the identification of 241 streptococcus strains. Organisms included 60 beta-hemolytic strains, 36 group D strains, 26 Streptococcus pneumoniae strains, and 119 viridans streptococcus strains. API correctly identified to species 68.3% of beta-hemolytic strains, 86.1% of group D strains, 53.9% of S. pneumoniae strains, and 12.6% of viridans streptococci. This method provided excellent identification of group A and B and S. faecalis strains. Overall, API correctly identified 41.9% of strains to species, with 41.1% good likelihood but low selectivity, 15.8% incorrect, and 1.2% not identified. GPI correctly identified to species 58.3% of beta-hemolytic strains, 97.2% of group D strains, 80.8% of S. pneumoniae strains, and 57.2% of viridans streptococci. Group A, B, and D strains were all accurately identified by this system. Overall, GPI correctly identified to species 66.0% of strains, with 8.7% correct preliminary identification, 20.8% incorrect, and 4.6% not identified. Both methods represent a worthwhile advance in streptococcal identification. Neither system, however, can be recommended for species identification of the viridans group at this time.
Enzymatic histamine synthesis by renal glomeruli of the rat has been examined. Assays of the partially purified enzyme demonstrated a pH optimum of 6.2, a Michaelis-Menten constant of 2.4 X 10(-4) histidine, and lack of potentiation by benzene. These data thus indicate that renal glomeruli contain the histidine-specific histidine decarboxylase.