Biomedical subjects

E N Hristova

Publications and source records attributed to E N Hristova.

5 recordsLinked to original sources

PubMed1997

Clinically important intermethod differences for physiologically abnormal ionized magnesium results.

We compared physiologically abnormal low and high ionized magnesium (iMg) results determined with the AVL 988-4 (AVL, Graz, Austria) and Nova CRT (Nova Biomedical, Waltham, Mass) ion-selective electrodes (ISEs) in serum samples from randomly selected patients. A result of < 0.39 mmol/L with either ISE constituted the low magnesium group and of > or = 0.65 mmol/L the high magnesium group. Within each group we found significant differences between the iMg results. Major intermethod differences were found for samples with physiologically normal total magnesium concentration: most of the samples in the low magnesium group (83%) had abnormally low results with the Nova ISE, whereas most of the results with the AVL ISE (83%) were normal. In contrast, all results with the AVL ISE for the high magnesium group were abnormally high, but 67% of the results with the Nova ISE were normal. The agreement for the clinical interpretation of iMg results based on the reference interval for each method was only 32%. The differences in iMg results between the two analyzers must be resolved before using the iMg test as measured with ISE for patient care.

Blood Chemical Analysis↗

PubMed1997

Serum ionized magnesium in chronic alcoholism: is it really decreased?

Chronic alcoholism is associated with a marked deficit in total magnesium (tMg). However, little is known about the status of the physiologically active form, ionized magnesium (iMg). We assessed serum iMg (measured with two ion-selective electrodes, AVL 988-4 and NOVA CRT) and tMg concentrations in chronic alcoholics at admission (n = 31) and after abstinence (n = 13) and compared these results with those for a control group (n = 40). At admission, the tMg and NOVA iMg concentrations in alcoholics (0.78 +/- 0.020 and 0.38 +/- 0.016 mmol/L, respectively) were significantly less (P <0.001) than in the controls (0.85 +/- 0.008 and 0.50 +/- 0.006 mmol/L). The AVL iMg results, however, did not differ significantly between the two groups: 0.53 +/- 0.013 vs 0.56 +/- 0.006 mmol/L, respectively (P >0.05). The mean iMg between the two analyzers differed significantly in both groups (P <0.001). After 3 weeks of abstinence, the alcoholics showed a significant increase in tMg (P <0.001) and in both NOVA and AVL iMg values (P <0.01 for each). tMg concentrations were positively correlated with the AVL iMg values in both alcoholics and controls but correlated positively with the NOVA iMg results only in the controls. Thus, the altered status of iMg is instrument-dependent, and the usefulness of the measurement in alcoholics is yet to be determined.

Adult↗

PubMed1996

Comparison of precision and effect of pH and calcium on the AVL and NOVA magnesium ion-selective electrodes.

We compared the precision of the AVL 988-4 and NOVA CRT instruments for determining ionized magnesium (iMg) and assessed the effect of pH and ionized calcium (iCa) concentration on the results Within-run and day-to-day precision for the iMg electrodes were determined using three levels of control material supplied by each manufacturer. The effect of pH on iMg results was assessed by analyzing anaerobic serum samples from patients, reanalyzing those same samples after pH was increased by in vitro loss of CO2 and comparing the results. To assess the effect of iCa concentration on the iMg results, we added CaCl2 to aqueous standards from both manufacturers and to a normal serum pool. The results show comparable coefficients of variation for the two iMg electrodes both within-run (0.68-2.05 for NOVA; 0.77-2.60 for AVL) and day-to-day (2.90-6.48 for NOVA; 1.71-4.93 for AVL). The AVL results were not affected by the increase in serum pH and agreed with the NOVA results that were adjusted to a pH of 7.4 (paired t-test; p > 0.2). There was a significant direct relationship between the iCa and iMg results for both analyzers, but the AVL slopes were smaller (0.026, 0.083) than the NOVA slopes (0.129, 0.165). Thus, these two iMg electrodes have comparable precision but differ in response to an increase in pH and iCa.

Calcium↗

PubMed1996

Linearity and stability of the AVL and Nova magnesium and calcium ion-selective electrodes.

We studied the stability and linearity of the AVL and Nova Mg and Ca ion-selective electrodes and the relation between the ionized Ca and ionized Mg results reported by each analyzer. The response of the electrodes to different concentrations of Mg and Ca was determined for saline solutions, aqueous solutions, and serum samples. The electrodes from both manufacturers demonstrated acceptable stability for the time of the study. The response of the electrodes was linear within the range specified by each manufacturer, but relative nonlinearity and the values for the linear limits differed between the AVL and Nova analyzers. The ionized Mg results varied with the concentration of Ca. The relation between ionized Ca and ionized Mg results was nonlinear and differed between the AVL and Nova electrodes. Intermethod comparison between the electrodes showed poor agreement for ionized Mg results, especially at low and high concentrations of total Ca and total Mg.

Calcium↗

PubMed1995

Analyzer-dependent differences in results for ionized calcium, ionized magnesium, sodium, and pH.

We compared two ion-selective analyzers (AVL 988-4 and NOVA CRT) for determining ionized calcium (iCa2+), ionized magnesium (iMg2+), sodium (Na+), and pH in serum specimens from healthy and diseased individuals. For assays of three levels of protein-based control materials, total imprecision (CV) was < 3% for all analytes except iMg2+ (< or = 6.5% on NOVA, and < or = 4.9% on AVL). We found a significant difference between the analyzers (P < 0.001) for the mean iMg2+ concentration in patients but no significant correlation (r = 0.253) between the analyzers for iMg2+ in specimens from healthy volunteers, even though the mean iMg2+ concentration did not differ significantly between these groups. The reference interval (central 95 percentiles) for iMg2+ with AVL (0.44-0.60 mmol/L) was contained within that of NOVA (0.39-0.64 mmol/L). The AVL gave higher values for iCa2+ (P < 0.001) and lower values for pH (P < 0.001) in specimens from normal volunteers and patients. The mean value for Na+ in patients' samples was significantly higher by the NOVA (P < 0.01) than by the AVL analyzer. Thus, we found significant differences between these two analyzers for all four analytes.

Calcium↗