Homogeneous enzyme immunoassay for tobramycin evaluated and compared with a radioimmunoassay.

Abstract We evaluated a commercially available homogeneous enzyme immunoassay (EMIT, Syva Co.) for tobramycin against a reference radioimmunoassay (RIA) method. Between-assay precision (CV) was 2.9% at 6.2 mg/L and 3.0% for values in the range of 1.0-7.6 mg/L. Accuracy based on a recovery experiment (1.0-13.0 mg/L) yielded an analytical recovery of 88-112%. A correlation study with 75 sera from patients on tobramycin therapy showed that EMIT = 0.984 RIA - 0.0808, r = 0.993. Neither the EMIT nor the RIA procedure was affected by the presence of gentamicin, amikacin, and vancomycin. Absorbance data from the EMIT system calculated with the conventional RIA logit-log algorithm correlate well with results generated by the Syva data-handling system (logit-log = 1.077 Syva - 0.318, r = 0.998). A reagent stability study indicated that the EMIT reagents, once reconstituted, remain stable for at least 17 days when stored at refrigerated temperatures, or 11 days if stored at room temperature, thus enabling frequent "stat" assays without the need to prepare a calibration curve each time.

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Homogeneous enzyme immunoassay for cortisol with a centrifugal analyzer.

Clinical Chemistry ◽

10.1093/clinchem/30.11.1824 ◽

1984 ◽

Vol 30 (11) ◽

pp. 1824-1826 ◽

Cited By ~ 3

Author(s):

J M Izquierdo ◽

A Quirós ◽

J Alvarez-Uría ◽

P Sotorrío

Keyword(s):

Enzyme Immunoassay ◽

Protein Complex ◽

Acidic Solution ◽

Serum Cortisol ◽

Standard Curve ◽

Analytical Recovery ◽

Target Values ◽

Assay Precision ◽

Homogeneous Enzyme Immunoassay ◽

Control Samples

Abstract We determine serum cortisol by a homogeneous enzyme immunoassay in the Cobas Bio centrifugal analyzer. To unbind cortisol from its protein complex, serum is treated for 15 min with an acidic solution. The reaction then proceeds automatically in the analyzer at 37 degrees C. To 50 microL of sample mixture is added 125 microL of reagent (cortisol antibodies, glucose 6-phosphate, and NAD+). This mixture is incubated for 60 s, after which 25 microL of a cortisol derivative labeled with glucose 6-phosphate is added; the increase in absorbance is monitored at 340 nm. The standard curve was linear from 10 to 500 micrograms of cortisol per liter. Within-assay precision (CV) varied from 0.2 to 0.6%, between-assay precision from 6.2 to 10.6%. Analytical recovery ranged from 100 to 103%. Results for control samples deviated from target values by 1.4 to 7.8%. Results compared well with those by radioimmunoassay. The method is reliable and practicable and will usefully replace previous routine methods for serum cortisol.

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Enzyme immunoassay of thyroxin with a centrifugal analyzer.

Clinical Chemistry ◽

10.1093/clinchem/28.1.123 ◽

1982 ◽

Vol 28 (1) ◽

pp. 123-125 ◽

Cited By ~ 2

Author(s):

J M Izquierdo ◽

P Sotorrío ◽

A Quirós

Keyword(s):

Fatty Acids ◽

Enzyme Immunoassay ◽

Protein Complex ◽

Standard Curve ◽

Analytical Recovery ◽

Target Values ◽

Assay Precision ◽

Homogeneous Enzyme Immunoassay ◽

Control Samples

Abstract We have applied a homogeneous enzyme immunoassay for determination of thyroxin in serum to the "Cobas Bio" centrifugal analyzer. To unbind thyroxin from its protein complex, serum is treated for 20 min with a solution of NaOH containing "Lipex," an agent for sequestering free fatty acids. The immunoenzymic reaction is then automatically performed by the analyzer at 37 degrees C. To 20 microL of sample mixture is added 125 microL of reagent (thyroxin antibodies and NAD+) and this mixture is incubated for 10 s. Then 25 microL of start reagent (enzyme-thyroxin conjugate and malate substrate) is added and the change in absorbance is monitored at 340 nm. The standard curve is linear up to at least 200 micrograms of thyroxin per liter. Within-assay precision (CV) varied from 1.1 to 2.9%, between-assay precision from 3.1 to 7.8%. Analytical recovery of thyroxin was complete. The deviation of control samples from target values ranged from -2.1% to 7.0%. Interference by hemoglobin or bilirubin is negligible. Results compare favorably with those by radioimmunoassay.

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Free and total insulin as determined after precipitation with polyethylene glycol: analytical characteristics and effects of sample handling and storage.

Clinical Chemistry ◽

10.1093/clinchem/33.1.93 ◽

1987 ◽

Vol 33 (1) ◽

pp. 93-96 ◽

Cited By ~ 55

Author(s):

H Arnqvist ◽

P O Olsson ◽

H von Schenck

Keyword(s):

Polyethylene Glycol ◽

Room Temperature ◽

Serum Samples ◽

Sample Handling ◽

Insulin In Plasma ◽

Analytical Recovery ◽

Free Insulin ◽

Assay Precision ◽

And Storage ◽

Collection Time

Abstract We evaluated results of radioimmunoassays of free and total insulin after precipitation of endogenous antibodies with polyethylene glycol (PEG), and we investigated the influence of collection time, temperature, and storage in heparin- cr EDTA-treated plasma or serum on results for free insulin. Analytical recovery of free insulin was 99.3%, of total insulin 96.4%. For free insulin, assay precision (CV) was 4.0-13.0% (intra-assay) and 7.8-10.7% (inter-assay); for total insulin, 3.6-9.5% and 6.6-11.7%, respectively. Free insulin decreased in plasma (p less than 0.05) and serum (p less than 0.01) at room temperature after 3 h and in promptly analyzed serum (p less than 0.01). Storage of samples at -20 degrees C increased the concentration of free insulin in plasma (p less than 0.025) and serum (p less than 0.005), whereas the free insulin content of supernates after PEG precipitation was stable, except for a slight decrease in serum samples (p less than 0.02). We conclude that, for radioimmunoassay of free and total insulin, plasma should be used, treated with PEG without delay; supernates then are analytically stable for as long as 26 weeks at -20 degrees C.

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Stability of standard curves prepared for EMIT homogeneous enzyme immunoassay kits stored at room temperature after reconstitution.

Clinical Chemistry ◽

10.1093/clinchem/26.5.652 ◽

1980 ◽

Vol 26 (5) ◽

pp. 652-654 ◽

Cited By ~ 4

Author(s):

P R Bach ◽

J W Larsen

Keyword(s):

Enzyme Immunoassay ◽

Room Temperature ◽

Palo Alto ◽

Parallel Increase ◽

Absorbance Changes ◽

The Stability ◽

Time Standard ◽

Homogeneous Enzyme Immunoassay ◽

Product Literature

Abstract We examined the stability of standard curves obtained with use of homogeneous enzyme immunoassay reagents (EMIT; Syva Corp., Palo Alto, CA) for assay of lidocaine, procainamide, N-acetylprocainamide, gentamicin, and theophylline, when stored at room temperature (23-24 degrees C) after reconstitution of the lyophilized materials. Standards were run and curves obtained for as long as 16 days after reconstitution. All standard curves were acceptable, according to the criteria specified in Syva product literature. Absorbance changes for all calibrators, including the zero calibrator, increased gradually with time. Increases of non-zero calibrators were largely offset by a parallel increase in the zero calibrator, such that the quantity delta A--delta A0 was very nearly constant with time. Standard curves based on the quantity delta A--delta A0 can be used for longer than curves based only on delta A.

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Stability of standard curves prepared for EMIT homogeneous enzyme immunoassay kits stored at room temperature after reconstitution.

Clinical Chemistry ◽

10.1093/clinchem/26.5.0652 ◽

1980 ◽

Vol 26 (5) ◽

pp. 652-654 ◽

Cited By ~ 1

Author(s):

P R Bach ◽

J W Larsen

Keyword(s):

Enzyme Immunoassay ◽

Room Temperature ◽

Palo Alto ◽

Parallel Increase ◽

Absorbance Changes ◽

The Stability ◽

Time Standard ◽

Homogeneous Enzyme Immunoassay ◽

Product Literature

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Evaluation of a new valproic acid enzyme immunoassay and comparison with a capillary gas-chromatographic method.

Clinical Chemistry ◽

10.1093/clinchem/27.1.169 ◽

1981 ◽

Vol 27 (1) ◽

pp. 169-172 ◽

Cited By ~ 12

Author(s):

S L Braun ◽

A Tausch ◽

W Vogt ◽

K Jacob ◽

M Knedel

Keyword(s):

Valproic Acid ◽

Enzyme Immunoassay ◽

Chromatographic Method ◽

Comparison Method ◽

Manual Method ◽

Analytical Recovery ◽

Significant Difference ◽

High Concentrations ◽

Assay Precision ◽

Gas Chromatographic Method

Abstract A new homogeneous immunoassay (EMIT) for valproic acid was evaluated. Besides testing the manual version of this enzyme immunoassay, we also developed two mechanized procedures for centrifugal analyzers (the CentrifiChem and the COBAS system), which take less time and are more precise than the manual method. Within-assay precision (CV) was 4.5% with the manual technique and 2% with the analyzers. Between-assay precision (CV) ranged from 4 to 13% for all three techniques. Accuracy of th manual method was checked by dilution and analytical recovery experiments. Our comparison of the EMIT results with those obtained by a comparison method (capillary gas chromatography) showed no significant difference. No interference from hemolysis, hyperbilirubinemia, or aliphatic amino acids was observed. At high concentrations of bile acids and with lipemic sera the analytical recovery rates decreased slightly, to 87% and 92%, respectively.

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