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R Valdes

Publications and source records attributed to R Valdes.

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

Endogenous digoxin-like immunoreactivity in elderly patients with normal serum creatinine concentrations.

The effect of digoxin-like immunoreactive substance (DLIS) on serum digoxin determinations in elderly patients with normal serum creatinine concentrations was studied. Patients in the study group were over 70 years of age; the control population was under 55 years of age. All patients had serum creatinine concentrations of less than or equal to 1.5 mg/dL. Apparent digoxin content of serum samples from patients receiving digoxin and from patients in each age group who were not receiving digoxin was determined in duplicate by each of two radioimmunoassays: RIANEN (New England Nuclear), which detects DLIS, and Immophase (Corning Medical and Scientific), which is far less cross-reactive with DLIS. Results from the patients under 55 years of age were analyzed for inherent bias between the assay methods. In patients over 70 years of age, concentrations of DLIS (differences between serum digoxin concentrations measured by RIANEN and Immophase) were compared with creatinine clearance values. No DLIS was detected in sera of patients who had not received digoxin. For patients who received digoxin, nearly all apparent digoxin concentrations were within the usual therapeutic range. For patients without liver or renal failure who received digoxin, no significant difference in digoxin concentrations was observed between the RIANEN and Immophase assays in either the young (n = 17) or elderly (n = 26) patients. There was no significant increase in the difference between the RIANEN and Immophase results with decreasing creatinine clearance. In the elderly patients with normal serum creatinine concentrations, there was no evidence that measurement of serum digoxin concentration using the RIANEN and Immophase assays was compromised by DLIS.

Adult↗
PubMed1987

Effect of tetrasodium EDTA on enzymatic determinations of urinary oxalate.

We studied the effects of pretreating urine samples with tetrasodium EDTA (TEDTA) before measuring urinary oxalate with an enzymatic kit (Sigma). Mean analytical recovery of added oxalic acid was only 49% (SD +/- 13%) when the assay was performed as recommended by the manufacturer, but treating samples with TEDTA improved recoveries (96 +/- 10%). In 20 unselected 24-h urine samples assayed with and without TEDTA treatment, the mean oxalate concentrations were significantly (P less than 0.001) different: 15.6 +/- 8.7 and 12.2 +/- 7.9 mg/L, respectively. TEDTA-treated urine samples stored for 14 days at -20 degrees C lost 20% of their oxalate concentration. Use of TEDTA simplifies sample preparation by eliminating the alkalinizing step needed to dissolve EDTA or disodium EDTA.

Edetic Acid↗
PubMed1987

Endogenous digoxin-like immunoreactive factors eliminated from serum samples by hydrophobic silica-gel extraction and enzyme immunoassay.

Elimination of endogenous digoxin-like immunoreactive factors (DLIF) that interfere with accurate measurement of digoxin requires use of a highly specific anti-digoxin antibody, or that DLIF be separated from digoxin before immunoassay. Several commercial digoxin-assay kits include a step for separating serum proteins and other substances from digoxin before immunoassay. We tested six different immunoassay methods (some having pretreatment steps) for their ability to detect DLIF in serum from patients in renal failure, pregnant women, and neonates, all of whom were not taking digoxin. Extracting digoxin on a column of derivatized silicagel eliminated detectable DLIF from serum as measured by enzyme immunoassay (EMIT; Syva Co.), but recovery of added digoxin was quantitative. In contrast, protein precipitation with 5-sulfosalicylic acid left significant amounts of DLIF in samples, most probably because the procedure (TDx assay; Abbott Labs.) disrupted protein-DLIF binding. A glass-bead radioimmunoassay (Immophase; Corning Medical) had the most digoxin-specific antisera. By preparative silica-gel-chromatography of serum we could eliminate or significantly minimize inaccurate digoxin measurements attributable to endogenous DLIF.

Blood Proteins↗
PubMed1987

Improved interassay correlation of digoxin results in patients with and without renal failure by elimination of digoxin-like immunoreactive factors.

Use of immunoassays that do not detect endogenous digoxin-like immunoreactive factors (DLIF) in serum significantly improves the between-assay correlation of digoxin results for patients. We investigated five different immunoassay methods (Abbott, Clinical Assays, Corning, Du Pont, and Syva), measuring digoxin by all five assays in sera from 38 patients in renal failure and in 40 patients with normal renal function, all taking digoxin. The mean standard error of the estimate (Sy X x) of digoxin results (compared for all five assays) were significantly lower for patients with normal renal function than for patients in renal failure (0.148 vs 0.293 microgram/L, P less than 0.001). Assays previously shown (Clin Chem 1987;33:401) to be the least sensitive to DLIF (Syva and Corning) gave the lowest mean scatter about the regression (Sy X x = 0.192 microgram/L, renal failure; 0.114 microgram/L, normal renal function) for all 10 assay correlations. Evidently, discrepancies between digoxin values as measured by different immunoassay kits for patients with renal disease can be attributed to DLIF. Moreover, because inaccurate digoxin results attributed to DLIF may not be limited exclusively to groups of patients with known increased concentrations of DLIF, the possibility of "latent" DLIF interference may be a problem in many other human subjects.

Blood Proteins↗
PubMed1987

Criteria for evaluating nonquantitative assays: application to serum choriogonadotropin.

We present guidelines for assessing the performance of nonquantitative (qualitative) assay methods. Criteria to be evaluated include analytical sensitivity, imprecision near limits of detection, analytical specificity, accuracy over a wide range of analyte concentrations, potential interferents, and technical ease of performance. A protocol was developed to evaluate several nonquantitative assay kits for detection of human choriogonadotropin (hCG) in serum. These include Tandem Icon HCG (Hybritech), Quest Pregnancy Test (Quidel), Concep-7 beta hCG (Leeco), and Beta Quik V (Pacific Biotech). Quantitative measurement of beta-hCG by RIA (Immophase beta hCG, Corning Medical) was used as the reference method. Results of this evaluation are discussed. The guidelines established and utilized in this report are adaptable to the evaluation of assay kits that measure other analytes by qualitative techniques.

Chorionic Gonadotropin↗
PubMed1986

Modification of human haemoglobin with glucose 6-phosphate enhances tetramer-dimer subunit dissociation.

Studies using equilibrium gel-permeation chromatography demonstrate that formation of the covalent adduct of D-glucose 6-phosphate (G6P) with human haemoglobin promotes dissociation of the haemoglobin tetramer into its component alpha beta dimer pairs [Kdoxy = 2.57 X 10(-6) versus Kdoxy (G6P) = 11.22 X 10(-6) M-haem]. On the other hand, Kd for glucosylated haemoglobin is identical with those of the O2- and CO-liganded forms of intact haemoglobin A0. These data are consistent with the phosphate moiety alone being responsible for a 4.5-fold increase in the tetramer-to-dimer apparent Kd. This suggests the glucose 6-phosphate moiety does not bind to the same sites on haemoglobin as do the free organic phosphates, as suggested by ligand-binding kinetics data or structural analysis. My study presents a working model for studying changes in protein subunit assembly as altered by protein phosphorylations.

Binding Sites↗
PubMed1986

Implementation of a screening program for diagnosing open neural tube defects: selection, evaluation, and utilization of alpha-fetoprotein methodology.

We evaluated and compared three different commercial kit immunoassays for alpha-fetoprotein (AFP) before we implemented our neural tube defect screening program. Each kit can be used with either serum or amniotic fluid. Analytical recovery ranges for AFP reference sera within each kit's standard curve limits (in kilo-int. units/L) were 97-108% (7.5-180) for the Kallestad kit, 77-101% (21.8-436) for Amersham, and 92-100% (0-177) for Hybritech. CVs, within each manufacturer's standard-curve limits, for combined intra-assay (amniotic fluid pools) and inter-assay (kit serum controls) averaged 3.6-7.3% (Kallestad), 2.4-9.3% (Amersham (y) kit results showed a correlation of r = 0.97, y = 1.05x + 5.5 kilo-int. units per liter of maternal serum (n = 66; range, 2.0-98.5). Gestational age did not influence these assay correlations. The Kallestad AFP assay demonstrated a maternal serum positivity rate of 2.9% at greater than or equal to 2.5 (n = 655) and 8.9% at less than 0.5 (n = 423) multiples of the median. All kits performed well analytically.

Amniotic Fluid↗
PubMed1985

Protein binding of endogenous digoxin-immunoactive factors in human serum and its variation with clinical condition.

We previously identified endogenous digoxin-like immunoactivity in serum from pregnant women, newborn infants, and patients in renal failure. This activity is due to an endogenous factor(s) that cross-reacts with antibodies raised against digoxin. Using serum from the above sources as well as serum and urine from normal individuals, we further characterized these immunoreactive factors. The factors are water soluble, heat stable, and neutral in molecular charge. That isolated from serum has an apparent mol wt of 200 daltons, as estimated by membrane partitioning. The factor from urine has twice this apparent mol wt, an apparent higher affinity for the digoxin antisera, and is less resistant to acid hydrolysis. It may represent a conjugated metabolite of the factor from serum. The immunoactive factor in serum is noncovalently bound to serum protein, and we describe methods for estimating total, weakly protein-bound (i.e. heat-dissociable), tightly protein-bound (i.e. not heat-dissociable), and unbound (free) activity. Levels measured directly in serum by RIA represent the unbound and weakly protein-bound serum components. In normal subjects, over 90% of the total endogenous immunoactivity in serum is tightly but reversibly bound to protein and not detectable by direct measurement with conventional RIAs. Concentrations determined by direct measurement in serum from patients with renal failure [128 +/- 38 pg digoxin equivalents/ml (mean +/- SE)], pregnant women (141 +/- 12), and neonates (230 +/- 7) consistently exceeded those in normal subjects (61 +/- 3). Chromatography and ultrafiltration studies suggest that these differences are due to increased amounts of weakly protein-bound factor in these subjects rather than to a greater amount of total immunoactive factor. Altered protein binding of this endogenous factor seems to play a predominant role in the detection of digoxin-like immunoactivity in human serum. Our data also suggest that carrier proteins may play a prominent role in the transport of this endogenous immunoactive factor in blood.

Adult↗
PubMed1985

Endogenous digoxin-immunoactive factor in human subjects.

Endogenous digoxin-like immunoactivity has been detected in the blood of adult patients in renal failure, newborn infants, and pregnant women in the third trimester. Blood levels of this activity increase in pregnant women as gestation progresses, and preliminary data suggest that the activity is increased in hypertensive pregnant women relative to normotensive pregnant women. Similar immunoactivity has also been detected in amniotic fluid and in the urine and serum of normal healthy subjects. The factors giving rise to this immunoactivity cross-react with antibodies used in many commercially available immunoassays for digoxin. The immunoactive factor isolated from human subjects is water soluble and exists tightly but reversibly bound to proteins in serum. The extent of this protein binding is altered in the clinical conditions studied relative to normal adults. This altered protein binding accounts for the detection of this factor by many of the commercially used immunoassays for digoxin. In this article I summarize recent findings related to detecting this activity in the blood of several clinical populations where the accurate measurement of digoxin may be compromised. I also summarize the preliminary isolation and characterization of the factor responsible for this immunoactivity.

Adult↗
PubMed1985

Endogenous digoxin-like immunoreactive factors: impact on digoxin measurements and potential physiological implications.

Various laboratories have reported endogenous digoxin-like immunoreactive factor(s) (DLIF) in blood from patients in renal failure or liver failure, from newborn infants, and from third-trimester pregnant women. Similar immunoreactivity has been detected in amniotic fluid, in cord blood, and in urine and serum from normal subjects. The factor(s) giving rise to this immunoreactivity cross react with antibodies used in many currently available immunoassays for digoxin, sometimes causing apparent digoxin concentrations exceeding the therapeutic range obtained for exogenous digoxin, with consequent errors in measurement and in subsequent clinical interpretation of digoxin results. Here, I summarize findings in our laboratory and those of others. DLIF evidently exist in three states in serum: tightly protein-bound, weakly protein-bound, and unbound (free). In normal subjects, greater than 90% of the total DLIF in serum is tightly but reversibly bound to serum proteins and is not readily detectable by direct measurement of digoxin in serum with conventional immunoassays. However, there seems to be a redistribution of the more weakly bound and unbound components in patients with renal failure, pregnant women, and newborns. The increased values detected in these groups are ascribable to increased amounts of weakly bound and unbound DLIF rather than to increased total DLIF. Carrier proteins may play a prominent role in the transport of these factors in blood. I discuss the potential physiological and pharmacological implications of detecting endogenous immunoreactive factors that cross react with antibodies to drugs.

Adult↗
PubMed1985

Endogenous digoxin-immunoreactive substance measured in several patient populations.

We have reported the presence of endogenous digoxin-like immunoreactivity in the bloods of patients in renal failure, of newborn infants, and of third-trimester pregnant women. Similar reactivity has also been detected in amniotic fluids and in the urine and serum of normal healthy subjects. The substance(s) giving rise to this immunoactivity cross-react with the antibodies used in many commercially available immunoassays for digoxin. In this brief review I summarize the findings of our laboratory in detecting this activity in the bloods of several clinical populations where the accurate measurement of digoxin may be compromised. Present data suggests the substance or group of substances being detected by these immunoassays are not one or a combination of elevated steroids or polypeptides commonly observed in these same clinical conditions. Some preliminary information on the physical characterization of this activity is also presented.

Digoxin↗
PubMed1985

Endogenous digoxin immunoactivity is elevated in hypertensive pregnancy.

We have detected an endogenous digoxin-immunoreactive substance in the blood of third trimester pregnant women, of newborn infants and in amniotic fluids. In this report we present data showing an increase in blood levels of this endogenous substance in pregnant women with time of gestation (45 +/- 12, 125 +/- 32, and 195 +/- 27 pg/ml digoxin-equivalent for the 1st, 2nd, and 3rd trimesters, respectively, mean +/- SE). Preliminary evidence suggests the blood level of this substance is elevated in third-trimester hypertensive pregnant women (315 +/- 29 pg/ml). The immunoactive substance isolated from pregnant subjects is water soluble and reversibly bound to serum proteins. Heating the serum increases the measured immunoactivity. Exploration of the physiologic relevance of this endogenous substance or family of substances is in progress.

Digoxin↗
PubMed1984

Comparative study of the ability of four aminoglycoside assay techniques to detect the inactivation of aminoglycosides by beta-lactam antibiotics.

In vitro inactivation of aminoglycosides (tobramycin, gentamicin, and amikacin) by beta-lactams (cefazolin, cefotaxime, moxalactam, carbenicillin, piperacillin, mezlocillin, and azlocillin) was measured using the enzyme-mediated immunoassay (EMIT), fluorescence polarization immunoassay ( TDX ), radioimmunoassay (RIA), and bioassay. No significant inactivation of aminoglycosides was produced by high levels of the three cephalosporins as measured by EMIT, RIA, or bioassay. Inactivation of tobramycin and gentamicin by mezlocillin and azlocillin was comparable to that seen with piperacillin but less than that with carbenicillin. In general, the bioassay detected the greatest degree of aminoglycoside inactivation and the EMIT assay detected the least for all drug combinations. The TDX and RIA techniques were equivalent in their ability to detect aminoglycoside inactivation by beta-lactam antibiotics.

Aminoglycosides↗
PubMed1984

Variable cross-reactivity of digoxin metabolites in digoxin immunoassays.

The authors investigated the cross-reactivity of the major known digoxin metabolites--digoxigenin, digoxigenin monodigitoxoside, digoxigenin bisdigitoxoside, and dihydrodigoxin--and of digitoxin in three 125I-radioimmunoassays and one enzyme immunoassay for digoxin. Digitoxin and dihydrodigoxin exhibit low cross-reactivity and nonparallel dilution responses for these assays. The cross-reactivities of the other three substances are significant for all assays studied with digoxigenin and monodigitoxoside having nonparallel and enhanced tracer displacement compared with digoxin itself. The authors demonstrate that because of nonparallel tracer displacement estimates of cross-reactivity calculated by the 50% displacement method fail to adequately predict the error induced in digoxin assays by digitoxin. They conclude that digoxin metabolites in serum are measured to various extents as the parent digoxin compound by all of the immunoassays they studied. In view of the varying biologic activity of digoxin metabolites and the large patient to patient variations in digoxin metabolism, the cross-reactivities the authors observe may help to explain the discrepancies in correlation of clinical response to measured serum digoxin values reported in other studies.

Cross Reactions↗
PubMed1984

Endogenous digoxin-immunoreactive substance in human pregnancies.

We report the presence of an immunoreactive digoxin-like substance in blood from third trimester pregnant women. The sera from 51 women in the third trimester of pregnancy were analyzed by 4 commercially available digoxin RIAs. None of these patients was receiving digoxin. Digoxin immunoreactivity was detected in all patients by 3 of 4 assays. The measured values, in nanograms per ml digoxin equivalent, were (mean +/- SD): method A, 0.27 +/- 0.05; method B, 0.28 +/- 0.07; method C, 0.01 +/- 0.01; and method D, 0.15 +/- 0.06. Method B measured values greater than 0.50 ng/ml in sera from 5 patients. Digoxin immunoactivity was not detectable 24 h postpartum, suggesting a half-life in serum of 6 h or less. Exogenous digoxin added to these serum samples resulted in quantitatively additive increments above the endogenous measured levels. Three of 4 digoxin RIAs did not distinguish between true digoxin and the endogenous substance present in the sera of third-trimester pregnant patients. Preliminary evidence suggests that the endogenous digoxin immunoactivity is not due to elevation of levels of major known steroids in the blood of these women. Clinical management of women requiring digoxin therapy during pregnancy, therefore, is complicated by the inability to assume the same therapeutic range of digoxin in serum during the third trimester of pregnancy as in adult nonpregnant individuals.

Adult↗
PubMed1983

Estrogen and progesterone receptor assays on breast carcinoma from mastectomy specimens.

To determine whether autolytic loss of estrogen (ER) and progesterone (PgR) receptors might affect results of assays performed on primary carcinoma samples taken from fresh mastectomy specimens rather than from biopsy specimens, a group of 71 cases were examined, in which both types of samples were assayed. The comparisons showed a small significant reduction in the proportion of positive ER assay results in mastectomy-primary specimens compared with biopsy specimens, although the frequency of high-binding ER results in the mastectomy-primary specimens was not reduced. The number of positive PgR assays on mastectomy-primary specimens was not reduced in comparison with biopsy specimens. Correlation coefficients for ER values in the paired data were r = 0.836 for biopsy versus mastectomy, and r = 0.795 for primary tumor versus nodal metastasis. For PgR biopsy versus mastectomy r = 0.664, and for PgR primary versus node r = 0.352. The mean quantitative ER and PgR values were significantly higher in axillary lymph nodal metastases than in primary carcinomas, and the higher nodal receptor levels were explained in part by significantly higher tumor cellularity. It is concluded that while loss of ER sufficient to cause a false-negative interpretation may possibly occur in a few cases during the course of mastectomy, as a general rule, significant losses do not occur. The performance of assays on axillary metastases in mastectomy specimens is advantageous because of their high cellularity.

Axilla↗
PubMed1983

Endogenous substance in newborn infants causing false positive digoxin measurements.

We report the detection of a digoxin-like immunoequivalent substance in the plasma of neonates and infants and in amniotic fluid. Time-course studies in individual infants indicate that the substance probably is produced endogenously and is not exclusively retained by the infants from external sources. Digoxin recovery studies demonstrated that the presence of this material caused falsely elevated digoxin values. Our results cast considerable doubt on the reliability and clinical utility of digoxin radioimmunoassay measurements on the serum or plasma of neonatal and infant patients.

Amniotic Fluid↗