Vadiraja V. Murthy

Leukocyte Esterase Activity in Effusion Fluid of Patients with Otitis Media

Fluid obtained during myringotomy and tube placement in 20 patients with middle ear effusions was assayed for leukocyte esterase activity using a quantitative spectrophotometric assay. This quantitative assay used the synthetic substrate, N-tosyl indoxyl alaninate. Seven of the 20 samples showed no measurable enzyme activity (8 U/ml or less). The remaining samples demonstrated activity ranging from 20 to 1600 units. Although enzyme activity did not correlate well with the physical appearance of the fluid, it did correlate with clinical history, suggesting the presence of a purulent exudate rather than serous effusion. Leukocyte esterase activity in the fluid appears to hold promise as an indicator for the presence of chronic middle ear infection. The enzyme can be assayed by a simple and fast diagnostic strip test, with results available almost immediately.

Troponin-T as a serum marker for myocardial infarction

We report here our experience with serum troponin T(TnT), measured with the sandwich immunoassay introduced by Boehringer Mannheim as a marker for myocardial infarction. We assayed TnT in serial serum samples from 30 patients with time courses of serum CK, CK‐MB, AST, and LD that we consider typical of acute myocardial infarction (MI). In every patient but one, TnT rose in parallel with both CK‐MB and AST, but remained elevated significantly longer. The ratios of the elevations of the different markers varied from patient to patient with marked variation in the ratio of TnT to CK‐MB. There appeared to be a significant association between the magnitude of that ratio with the level of ALT. J. Clin. Lab. Anal. 11:125–128, 1997.

UNUSUAL INTERFERENCE FROM PRIMARY COLLECTION TUBE IN A HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY ASSAY OF AMIODARONE

We describe an unusual interference in our routine high‐performance liquid chromatography (HPLC) assay of amiodarone and its active metabolite, desethylamiodarone, used to quantify the parent drug and the active metabolite in serum from the primary sample collection tube. The interfering peak had a retention time very similar to that of the authentic desethylamiodarone. Substitution of Corvac tubes with Vacutainer tubes for the collection and transportation of serum samples eliminated the source of interference. We routinely suggest the use of Vacutainer collection tubes for obtaining blood samples of cardiac patients undergoing amiodarone therapy. J. Clin. Lab. Anal. 11:232–234, 1997.

Erythrocyte adenylate kinase isoenzyme as a marker for hemolysis.

The presence in serum of adenylate kinase isoenzyme originating from erythrocyte can be useful as a marker for detecting hemolysis. We have presented preliminary evidence for identifying hemolytic anemia patients earlier by determining erythrocyte AK isoenzyme activity in serum (or plasma) rather than using measurement of plasma hemoglobin concentration. This test being quite specific for hemolysis should find use as a quick method for estimating the extent of in vivo hemolysis in hemolytic patients earlier than heretofore possible. J. Clin. Lab. Anal. 11:351–356, 1997.

Differentiation and resolution of erythrocyte and muscle adenylate kinase activities in serum by electrophoresis.

Adenylate kinase activity originating from erythrocytes has been shown to be distinct from muscle adenylate kinase or myokinase activity, until now considered to be identical enzyme activities. The two activities can be differentiated by electrophoretic fractionation, thus making it possible to quantify the erythrocyte adenylate kinase activity present in serum. J. Clin. Lab. Anal. 11:235–237, 1997.

Lymphocytes produce specific alkaline phosphatase after in vitro stimulation or after in vivo infection with HIV‐1

A unique alkaline phosphatase isoform found in the serum of HIV‐1 infected patients is thought to originate from CD4 lymphocytes. Destruction of activated CD4 lymphocytes after HIV‐1 infection is probably responsible for the appearance of this isoform in circulation. This band‐10 alkaline phosphatase isoform is thus useful as an early marker for detecting AIDS in children born to HIV‐1 infected mothers.

Performance of opus immunoassays for thyroxine and beta-human chorionic gonadotrophin in serum

Two representative immunoassays for measuring thyroxine and β‐subunit of human chorionic gonadotrophin in serum, using the Opus immunoassay analyzer, were evaluated by comparing them to the reference RIA for T4 and β‐HCG enzyme immunoassay. Both assays were superior in accuracy and precision than the reference methods and exhibited good linearity throughout the concentration range needed for discriminating abnormally low and elevated concentrations from the established reference ranges of thyroxine and β‐human chorionic gonadotrophin in serum. Correlation between the results of the Opus immunoassays and the reference assays for T4 and β‐HCG was very good with correlation coefficients of 0.92 and 0.98, respectively.