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Biomedical subjects

M H Kroll

Publications and source records attributed to M H Kroll.

At least 73 records · Page 4Linked to original sources
PubMed1988

Control of platelet protein kinase C activation by cyclic AMP.

Experiments were performed to elucidate the role of adenosine 3': 5'-cyclic monophosphate (cAMP) in the control of platelet protein kinase C (PKC) activation. Platelet aggregation and secretion in response to 4 beta-phorbol 12-myristate 13-acetate (PMA) or 1-oleoyl-2-acetylglycerol (OAG) were inhibited by dibutyryl cAMP in a dose-dependent manner. Inhibition of these functional activities paralleled a decrease in the PMA-induced phosphorylation of the Mr 47,000 substrate (p47) of PKC by pre-incubation of platelets with dibutyryl cAMP. These changes were also observed when platelet cAMP was increased by prostacyclin (PGI2), forskolin, or theophylline. The ADP scavenger creatine phosphate/creatine phosphokinase (CP/CPK) and the cyclooxygenase inhibitor indomethacin also diminished the aggregation and p47 phosphorylation responses to PMA or OAG. Pre-incubation of platelets with dibutyryl cAMP significantly potentiated the inhibition of aggregation and p47 phosphorylation effected by CP/CPK and indomethacin. These results are consistent with the model that PMA- or OAG-induced activation of platelets is amplified by secreted ADP and that the response to secreted ADP is inhibited by cAMP. Furthermore, the findings that increased intracellular cAMP inhibits PMA- or OAG-induced p47 phosphorylation in excess of that due solely to CP/CPK, and that cAMP significantly potentiates the effects of ADP removal and inhibition of cyclooxygenase in blocking p47 phosphorylation suggest that cAMP also exerts non-ADP-mediated inhibitory effects on PKC in intact platelets.

Adenosine Diphosphate↗
PubMed1988

Analytical bias for cholesterol and the percent of the population deemed at risk for coronary heart disease.

The effect of methodological bias on the population at risk is dependent on the location of the reference value in the distribution of the population. We fitted the cumulative distribution for cholesterol to a rational function and calculated the apparent reference values for four biased methods: Technicon SMAC (2.6%), DuPont aca (4.0 to 4.8%), Kodak DT-60 (-2.0 to -5.5%), and BMD Reflotron (-7.4 to -7.8%). With the true and apparent reference values for cholesterol and the rational function, we determined the percentage increase or decrease in the population deemed at risk for coronary heart disease. The population at risk increased by as much as 48% for methods with positive bias, and decreased by as much as 54% for methods with negative bias. If we restrict the percentage of the population incorrectly diagnosed to 3% and use reference values (cut points) recommended by the National Cholesterol Education Program, the maximum allowable methodological bias would be 1.6% for positive bias and -1.55% for negative bias. Therefore, an absolute methodological bias of 3% (as recommended by the Laboratory Standardization Panel) may be too liberal.

Adult↗
PubMed1988

A model for the effect of bias for cholesterol on the population at risk.

The location of the Reference Value for an analyte within the population distribution affects the magnitude of error due to methodological bias. Using the gaussian distribution, we evaluated the effects of systematic and proportional biases of the method (positive and negative), mean value, and standard deviation on the magnitude of error. We chose four Reference Values for cholesterol as a model. For a population with a mean of 2.0 and SD of 0.36 g of cholesterol per liter, a 3% positive proportional bias causes sixfold more error at the 50th percentile than at the 97.5th. In general, the error for a given bias (proportional or systematic) is greater for a Reference Value within the body than at the tails of the distribution. Further, the magnitude of the error varies as a function of the mean and standard deviation of the population.

Cholesterol↗
PubMed1988

Bias between enzymatic methods and the reference method for cholesterol.

Assaying 312 serum samples, we compared four enzymatic methods for serum cholesterol with the Reference Method (modified Abell-Kendall) of the Centers for Disease Control (CDC). The means for the aca, TDx, and SMAC methods (2.27, 2.27, and 2.24 g/L, respectively) were significantly higher (P less than 0.05) than those of the Reference Method and the RA-1000 method (2.19 and 2.18 g/L, respectively). The biased methods had positive proportional and (or) systematic biases. Results with these methods were 2.6% to 4.9% higher than with the Reference Method. The assigned concentrations of cholesterol in the calibration materials for the SMAC and aca agreed with those obtained by the Reference Method, but were lower for the TDx and higher for the RA-1000. These findings document positive biases for cholesterol with three enzymatic methods and suggest that misassignment of calibrators is not primarily responsible for the biases found with the aca and SMAC. It may, however, to be a significant factor for the TDx.

Autoanalysis↗
PubMed1988

An enzymatic method for 5-fluorocytosine.

We developed an enzymatic method for determination of 5-fluorocytosine in serum, using creatine iminohydrolase (EC 3.5.4.21), the Cobas-Bio analyzer, and an extant ammonia method. Analytical recovery (y) of drug added to serum (x) was good, with y = 0.97x-0.7, Sy.x = 3.6, r = 0.997 (n = 65) over the range 6.25 to 150 mg/L. Comparison with an HPLC method (x) showed good agreement: y = 0.98x + 1.34, Sy.x = 3.7 (n = 37), as analyzed with the Deming debiased regression. Precision was good, CVs being less than 3% for within-run and less than 6% for between-run controls. Ammonia, amphotericin B, glucose, urea, and hemolysis do not interfere, but bilirubin shows analyte-dependent interference and lipemia interferes when triglycerides exceed 5 g/L. This assay is accurate, inexpensive, and easy to perform. It can be easily adapted for routine or emergency use.

Aminohydrolases↗
PubMed1987

Rapid rise of serum acid phosphatase after irradiation of metastatic carcinoma of prostate.

An eighty-two-year-old man with metastatic prostatic adenocarcinoma was treated with radiation therapy to the lumbar region of the spinal column. A rapid rise in his acid phosphatase activities developed, increasing thirty-eight-fold in two days. He died on the second day post-therapy of hemorrhagic complications. The rapid increase in acid phosphatase activity was due to release from injured or dying prostatic adenocarcinoma cells.

Acid Phosphatase↗
PubMed1987

A model for assessing interference.

Most studies of analytical interference indicate the magnitude but not the type of interference. We developed a model for interference that assesses the magnitude of the following types of interference: independent of analyte concentration, dependent on analyte concentration, and a combination of the two. The experimental design for the model is an orthogonally arranged matrix with progressively increasing concentrations of analyte and interfering agent. Multiple regression with these independent variables (concentration of analyte, concentration of interfering agent, and the product of the two) is used to determine the magnitude, direction, and significance of each type of interference. Applying the model to study interference by hemoglobin with determinations of creatinine, direct bilirubin, and total bilirubin showed that hemoglobin interferes with determination of creatinine independent of the analyte concentration, interferes with total bilirubin dependent on the analyte concentration, and interferes with direct bilirubin by a combination of these two.

Bilirubin↗
PubMed1987

Mechanism of interference with the Jaffé reaction for creatinine.

We investigated the mechanism of the Jaffé reaction for determination of creatinine by studying the spectrophotometric, kinetic, and equilibrium properties of the reaction of picrate with creatinine and with cyclic and aliphatic ketones. Absorbance spectra for the reaction products of picrate with all the ketones were superimposable with that of creatinine (Amax, 490 nm). Cyclic ketones not containing nitrogen had a molar absorptivity less than half that of creatinine and equilibrium constants approximately 0.01 that of creatinine. Aliphatic ketones, except for benzylacetone, had molar absorptivities similar to that of creatinine, but all of these compounds had equilibrium constants approximately a tenth or less that of creatinine. The common structure for all of the compounds reacting with picrate is the carbonyl group. The variable magnitude of interference for aliphatic and cyclic ketones is ascribable to the different rate constants, molar absorptivities, and equilibrium constants as compared with creatinine. Structures adjacent to the carbonyl group significantly affect the absorptivity and equilibrium constant, but steric hindrance is the major factor affecting the rate of reaction. We postulate that the carbonyl group is required for the Jaffé reaction, and we suggest a mechanism for the reaction.

Acetohexamide↗
PubMed1987

Cefoxitin interferes with the "Clini-Skreen" column method for urinary 17-hydroxycorticosteroids.

Cefoxitin interferes with determination of urinary 17-hydroxycorticosteroids. The apparent concentration of hormone is increased from three- to 10-fold in samples from patients receiving cefoxitin when the Amberlite XAD-2 "Clini-Skreen" column is used. To determine the mechanism of interference, we reacted aqueous solutions of cefoxitin, cortisol, cortisone, and 11-deoxycortisol with phenylhydrazine; recorded the adsorption spectra; and determined the molar absorptivities and the equilibrium and rate constants. Also, we recorded the absorption spectra of phenylhydrazine with eight other cepha antibiotics and benzylpenicillin. Cortisol, cortisone, 11-deoxycortisol, and cefoxitin react with phenylhydrazine and absorb light with superimposable spectra and absorption maxima of 410 nm. The other antibiotics react with phenylhydrazine but absorbance maxima of the products vary, none being at 410 nm. Cortisol, cortisone, and 11-deoxycortisol react with phenylhydrazine 35-fold faster, have equilibrium constants ninefold greater, and have molar absorptivities 1.6 times that of cefoxitin. Thus, cefoxitin interferes with determination of urinary 17-hydroxycorticosteroids by forming a chromophore with the same absorbance maximum and with a molar absorptivity similar to cortisol, but much more slowly.

17-Hydroxycorticosteroids↗
PubMed1986

The method of determination must be considered in interpreting blood cholesterol levels.

Based on the results of recent clinical trials, physicians have been encouraged to screen and treat patients for hypercholesterolemia. Since the data from the Lipid Research Clinics (LRC) have been used to define the patient population that should be treated, a comparison of LRC cholesterol results with those obtained with two commonly used clinical laboratory instruments was performed. Both the Technicon SMAC and the Du Pont aca had positive bias compared with the LRC method. Therefore, many patients with cholesterol concentrations greater than 265 mg/dL (6.85 mmol/L) as determined by these routinely used methods have markedly lower levels determined by LRC methods. These findings not only indicate that rigorous interlaboratory standardization is required to conform to LRC reference values, but they also suggest that the clinician should be aware of these methodological considerations when the decision to treat hypercholesterolemia is made.

Autoanalysis↗
PubMed1986

Rapid enzymatic method for measurement of serum flucytosine levels.

Creatinine iminohydrolase (EC 3.5.4.21) quantitatively releases ammonia from flucytosine (5FC) as well as from creatinine. Using 39 sera from eight patients receiving the combination of amphotericin B with 5FC, we demonstrated that this rapid enzymatic reaction provides a valid measure of 5FC levels. The correlation coefficients (r), comparing this method with 5FC bioassay and high-pressure liquid chromatography measurements, were 0.78 and 0.87, respectively. This technique offers a precise alternative to the currently employed methods of measuring 5FC levels. In contrast to other methods, this enzymatic technique is rapid, simple, inexpensive, and has the potential for widespread availability.

Aminohydrolases↗
PubMed1986

Automated determination of urinary creatinine without sample dilution: theory and practice.

The rate of the Jaffé reaction depends on the concentration of sodium hydroxide; the pseudo-first-order rate constant of the reaction, at 37 degrees C in 10 mmol/L picrate solution, is 0.004 mmol/L. We formulated an automated method to determine urinary creatinine directly without manual sample dilution. The conditions are as follows: 10 mmol/L picrate and 60 mmol/L sodium hydroxide (final concentrations); ratio of sample to final volume, 1:41; temperature, 37 degrees C; wavelengths of measurement, 500 or 510 nm; interval of measurement, 30 to 90 s; and mode of measurement, kinetic. Determinations of creatinine in patients' samples by the new method compared favorably with those obtained with the AutoAnalyzer and aca. The run-to-run CVs were 3.6% or less, and the method was accurate for concentrations of creatinine up to 3000 mg/L. We recommend this method as a good replacement for the AutoAnalyzer or aca methods.

Autoanalysis↗
PubMed1985

Relationships between magnesium and protein concentrations in serum.

We determined concentrations of magnesium, total protein, albumin, and globulin in more than 74 000 serum specimens from patients and noted a direct linear relationship between the concentration of magnesium in serum and the concentrations of total protein, albumin, and globulin in serum. Albumin and magnesium concentrations are linearly related at high and low albumin concentrations; within the reference interval, however, the magnesium concentration is independent of the albumin concentration. Linear regression analysis suggests that 25% of the total serum magnesium is bound to albumin and 8% to globulins.

Blood Proteins↗
PubMed1985

How certain drugs interfere negatively with the Jaffé reaction for creatinine.

Phenacemide and cephalothin may interfere either positively or negatively with the determination of creatinine by the Jaffé reaction, depending on the analytical system. The drug-picrate chromophores maximally absorb within the first minute of reaction (21 s for phenacemide, 45 s for cephalothin), after which the absorbances decrease. Thus, these drugs negatively interfere in analytical systems involving kinetic measurements when the time interval of measurement includes the period of decreasing absorbance.

Autoanalysis↗
PubMed1985

Molar absorptivity and the blank correction factor.

In photometry, where both the product formed and one or several reactants absorb light at the same wavelength, the absorbance of the "blank" of the sample at the end of the reaction may be less than that measured at the beginning of the reaction, because of consumption of reactant(s). The blank correction factor for the determined result with one light-absorbing reagent is epsilon P / (epsilon P - epsilon R), where epsilon R and epsilon P are the molar absorptivities of the reagent and the product, respectively. We derived a factor for the case when more than one reagent absorbs light at the same wavelength as the measured product. This factor is independent of the concentration of reagent(s) and can correct the determined result or absorbance for the consumption of light-absorbing reagent(s) during the reaction.

Biuret Reaction↗
PubMed1985

Hemoglobin interference from in vivo hemolysis.

Laboratory values for specimens from a case of intravascular hemolysis showed that hemoglobin was significantly increased and thus could interfere with the determination of other analytes. We studied this problem by adding increasing amounts of purified hemoglobin (to a maximum concentration of 19.3 mg/L) to aliquots of pooled serum samples. The hemoglobin significantly interfered with the determination of only five analytes: albumin, aspartate aminotransferase, direct bilirubin, and total protein on the SMAC, and creatinine on the Astra. We propose that for cases of proven intravascular hemolysis, values for only the analytes not affected by hemoglobin should be reported. We find lactate dehydrogenase activity useful in assessing the components of in vivo hemolysis; the differences between serum and plasma values for potassium, lactate dehydrogenase, and hemoglobin are related to in vitro hemolysis. Criteria for specimen collection and assessment of type of hemolysis are proposed.

Autoanalysis↗
PubMed1985

Comparison of creatinine as determined with the Ames Seralyzer and by three Jaffé-based methods.

We compared results for urinary creatinine, serum creatinine, and creatinine clearance, as determined with the Ames Seralyzer, with results determined with the Beckman ASTRA, the DuPont aca, and Technicon's AutoAnalyzer and SMAC. Results for urinary creatinine from the Seralyzer differed significantly (p less than 0.05) from those obtained with the ASTRA and AutoAnalyzer, but not with the aca. The Seralyzer results for serum creatinine were at least 1.0 mg/L higher (p less than 0.05) than by the other three methods. Results for creatinine clearance from the Seralyzer were 8 to 11 mL/min lower (p less than 0.05) than results by the other three methods. These differences are related to the positive interference by bilirubin in the Seralyzer creatinine method. We also evaluated 23 other compounds for interference with these methods for creatinine.

Autoanalysis↗