Digoxin-like immunoreactive substances in chronic liver disease

Characterization of bilirubin interference in three commonly used digoxin assays

BACKGROUND

Due to the narrow therapeutic range of digoxin, determining serum/plasma digoxin concentrations is critical for assessing patients with congestive heart failure, atrial fibrillation, and certain types of arrhythmias. However, digoxin quantification by competitive immunoassays is susceptible to interferences that may alter the accuracy of its measurement in patient plasma. This study aimed to characterize the extent of bilirubin interference in three commonly used digoxin immunoassays.

METHODS

Digoxin concentrations were compared using the Beckman Coulter® Unicel DxI 800, the Vitros® 4600, and the Roche Cobas® 8000 in neat or digoxin-spiked icteric and non-icetric plasma samples. A mixing study was performed to demonstrate how digoxin quantification is affected by bilirubin. An equation was derived that predicts the response of the DxI 800, given known bilirubin and digoxin concentrations.

RESULTS

The DxI reported detectable concentrations of digoxin in high bilirubin samples with no added digoxin, while the Vitros® 4600 and Cobas® 8000 gave virtually undetectable results. Spiking digoxin into samples with elevated bilirubin concentrations resulted in a higher percent recovery for the DxI 800 when compared to the other two platforms. The mixing study also revealed an increase in the percent recovery in the DxI 800, while the Vitros® 4600 and Cobas® 8000 were comparable to the expected concentration of digoxin.

CONCLUSIONS

The DxI 800 is most prone to interference by bilirubin, while the Vitros® 4600 and Cobas® 8000 are relatively unaffected. Icteric samples should be interpreted with caution if digoxin quantification is needed, especially on the DxI 800 assay.

A Carrier-Mediated Transport of Toxins in a Hybrid Membrane. Safety Barrier between a Patients Blood and a Bioartificial Liver

Combination of detoxifying liver support systems with liver cell bioreactors may have additional benefits for the treatment of liver failure due to the replacement of known and unknown metabolic activities of the liver. However, the problem of side effects and possible risks caused by the use of animal hepatocytes or hepatoma cells remains unsolved which underlines the need of a safety barrier between the patients blood and the extracorporeal bioreactor. Passive filters do not meet the requirements of such membranes, because in liver failure desired and undesired molecules in the patients blood share similar physicochemical properties. That challanges the developement of biologically designed separation membranes. A hybrid membrane is formed by implementation of transport proteins into a highly permeable hollow fiber. The transport of free solutes and albumin bound toxins is tested in vitro in comparison with conventional high flux membranes. The transport characteristics for tightly albumin bound toxins are significantly improved for the hybrid membrane. The transport of albumin bound toxins across the membrane is not associated with albumin. The selectivity of the transport is evaluated in vivo. No significant loss of middle molecular weight hormones attached to other carrier proteins was observed. Neither transport of immunologically relevant proteins across the membrane nor loss of valuable proteins was measured. Also in vivo, a significant reduction of protein bound toxins and a transport of metabolically relevant solutes, like amino acids, was shown. The presented hybrid membrane may be used like an “intellegent membrane” as a safety barrier between the patients blood and cell devices.

Endogenous glycosides in critically ill patients

OBJECTIVE

To determine the incidence of critically ill patients displaying endogenous digitalis-like-immunoreactive substances (DLIS) and to examine the relationship of these hormones to routine laboratory variables, the underlying disease, myocardial function, hemodynamic status, severity of illness, systemic inflammation, and mortality rate.

DESIGN

Sera of 401 consecutive critically ill patients, not treated with cardiac glycosides, were analyzed for DLIS (digitoxin and digoxin, TDx; Abbott Diagnostics, North Chicago, IL) and endogenous ouabain. Normal values of endogenous ouabain were determined in 62 healthy volunteers. We measured pro- and anti-inflammatory mediators (L-selectin, tumor necrosis factor-alpha, interleukin-1beta, interleukin-2, interleukin-6, interleukin-10), C-reactive protein, and serum amyloid A protein as well as patients' Acute Physiology and Chronic Health Evaluation II and Goris scores. In a subgroup of patients with a pulmonary artery catheter (n = 95), we determined cardiac output, pulmonary artery occlusion pressure, systemic and pulmonary vascular resistance, left ventricular stroke volume, and right and left stroke work.

SETTING

Two surgical intensive care units of an university hospital.

SUBJECTS

Sera of 401 consecutive critically ill patients.

INTERVENTIONS

Blood sampling.

MEASUREMENTS AND MAIN RESULTS

Of the 401 patients tested, 343 had nonmeasurable DLIS concentrations (DLIS-negative), and 58 (14.5%) had positive digoxin (n = 18) or digitoxin (n = 34) concentrations (DLIS-positive) or were positive in both tests (n = 6). Mean endogenous ouabain concentrations were nine-fold increased in DLIS-positive (3.59 +/- 1.43 nmol/L) and three-fold increased in DLIS-negative (1.34 +/-.81 nmol/L) patients compared with controls (0.38 +/- 0.31 nmol/L). DLIS and ouabain concentrations closely correlated with the Acute Physiology and Chronic Health Evaluation II and Goris score and were associated with increased concentrations of transaminases, bilirubin, aldosterone, cortisol, serum creatinine, fractional sodium excretion, proinflammatory mediators, C-reactive protein, and serum amyloid A (p <or=.009). The hospital mortality rates of DLIS-positive and DLIS-negative patients were 12% and 3.2%, respectively, and for patients with ouabain concentrations above and below 2 nmol/L 38.6% and 0.6%, respectively. In DLIS-positive patients with pulmonary artery catheter (n = 23), cardiac output, stroke volume, and left ventricular stroke work were decreased, and pulmonary artery occlusion pressure and central venous pressure were increased (p <or=.009).

CONCLUSIONS

Different types of endogenous glycosides including endogenous ouabain are elevated in a significant proportion of critically ill patients. The occurrence of these substances is associated with increased morbidity and hospital mortality rates, possibly due to systemic inflammatory processes. DLIS but not endogenous ouabain concentrations were found to be related to left ventricular function.

Digoxin Assays: Frequent, Substantial, and Potentially Dangerous Interference by Spironolactone, Canrenone, and Other Steroids

Background: A case of digoxin toxicity resulted from falsely low values with the MEIA II assay for digoxin (AxSYM®; Abbott). The low results were caused by negative interference from canrenone and spironolactone, the latter of which has recently been advocated for the treatment of severe heart failure. Analytical interference from spironolactone has been reported, but little information is available for this effect with newer digoxin assays.

Methods: We examined nine assays (AxSYM, IMx®, TDx®, Emit®, Dimension®, aca®, TinaQuant®, Elecsys®, and Vitros®) for interference by spironolactone, canrenone, and three metabolites. Additionally, all routine digoxin measurements (AxSYM) over a period of 16.5 months (n = 3089) were monitored for interference.

Results: Suppression of the expected values by canrenone (3125 μg/L) was observed for the AxSYM (42% of expected value), IMx (51%), and Dimension (78%) assays. A positive bias was observed for the aca (0.7 μg/L), the TDx (0.62 μg/L), and the Elecsys (&gt;0.58 μg/L). Twenty-five of 669 routinely monitored patients had falsely low results. Nineteen of these had potentially toxic concentrations of digoxin (Emit; &gt;2.0 μg/L), although the AxSYM assay indicated therapeutic or less severe toxic concentrations (Δmax = 7.1 μg/L). Except for two unresolved cases, this was attributable to spironolactone, canrenone, hydrocortisone, or prednisolone. Standard doses of spironolactone (up to 50 mg/day) in patients with heart failure displayed inhibition &lt;11%.

Conclusions: The frequency and magnitude of the false-negative results particularly compromise the use of both microparticle enzyme immunoassays. Not only may toxic concentrations remain unidentified, but intoxication could occur should dosage be increased because of falsely low results. With 11 million digoxin tests/year ordered in the US, conceivably many patients could be adversely affected.

Postmortem digoxin-like immunoreactive substances (DLIS) in patients not treated with digoxin

Endogenous digoxin-like immunoreactive substances (DLIS) cross-react in immunoassays of digoxin. The postmortem rise in digoxin levels in patients treated with the drug may be due to its redistribution. It is unclear what is the contribution of DLIS to this increase and whether DLIS are present postmortem in patients not treated with digoxin. The objectives of this study were to determine whether DLIS are present after death in patients not treated with digoxin, whether a postmortem increase in DLIS is detectable and whether sampling site can affect DLIS concentrations. DLIS (measured as digoxin, TDx Abott) were determined in blood samples drawn antemortem from ICU patients; postmortem samples from femoral artery and cardiac chambers were taken at least 12 h after the death of these same patients. DLIS concentrations > or = 0.2 ng/ml were measured in 44 and 40% of patients antemortem and postmortem (femoral), respectively. No difference was found in DLIS levels between antemortem and postmortem femoral and cardiac samples. Age, ICU stay and postmortem sampling time did not affect the postmortem increase in DLIS. None of the levels was in the toxic range. DLIS may be present after death and their concentration does not increase postmortem. The interpretation of postmortem digoxin concentrations that fall in the therapeutic range should be done cautiously; such measurable levels do not necessarily indicate misuse or malicious intent even in patients who had not been treated with the drug.

Nutritional status in non-alcoholic subclinical porto-systemic encephalopathy

AIM: To understand the role of nutritional status in cirrhotic patients without clinical porto-systemic encephalopathy (PSE).

METHODS: Fifty-one non-alcoholic patients with cirrhosis without PSE were studied prospectively and compared with 20 healthy volunteers. The nutritional evaluation included serum prealbumin, albumin, transferrin, body mass index ( BMI ), mid-arm muscle circumference (MAMC), and grip power. The occurrence of subclinical PSE ( SPSE ) was defined when N20-N65 inter-peak latencies of median nerve-stimulated somatosensory evoked potentials were > 2.5 standard deviations of control means. Blood chemistries were tested within 12 h of somatosensory evoked potentials test and nutritional evaluation.

RESULTS: Twenty-five, 17 and 9 cirrhotic patients were graded as Child-Pugh class A, B, and C, respectively. Twenty-four (47.1%) patients developed SPSE. Cirrhotic patients with SPSE had lower serum albumin (2.8 mg/L ± 5 mg/L vs 31 mg/L ± 7 mg/L, P < 0.001) levels than those without SPSE. Prealbumin (106mg/L ± 57mg/L vs 125 mg/L ± 58 mg/L), transferrin (1.64 g/L ± 0.46 g/L vs 1.78 g/L ± 0.58 g/L), BMI (23.7 kg/m²± 2.7 kg/m²vs 25.3 kg/m²± 3.6 kg/m²), MAMC (22.2 cm ± 2.6 cm vs 22.7 cm ±3.5 cm), and grip power (26.3 kg ± 6.4 kg vs 26.9 kg ± 6.8 kg) were not different between cirrhotic patients with and without SPSE. N20-N65 inter-peak latencies were correlated with serum albumin levels (P = 0.01) but not with prealbumin, transferrin, BMI, MAMC, or grip power. Serum albumin, prealbumin and transferrin levels were different among cirrhotic patients with Child-Pugh classes A, B, and C (P < 0.05). BMI, MAMC, and grip power were not different among Child-Pugh classes A, B and C.

CONCLUSION: Our data suggest that serum albumin level is a simple test in the evaluation of nutritional status in patients with cirrhosis.

Quantitation of interference in digoxin immunoassay in renal, hepatic, and diabetic disease

A comparison of the results of a newly developed fluorescence-derivatization/HPLC method and a commercial immunoassay method (ACA, Dupont) for the measurement of serum digoxin concentrations in patients indicates that (1) the results from the ACA method agree well with those from the HPLC method in patients with cardiovascular disease but without renal, diabetic, and liver disease, (2) serum digoxin concentrations determined by the ACA method are overestimated in patients with renal, diabetic, or liver disease, and (3) the steady-state serum concentrations of hydrolyzed and reduced metabolites are relatively insignificant in patients receiving digoxin therapy, including patients with renal failure. The excellent reproducibility of the HPLC and immunoassay methods (coefficient of variation < 9.0%), together with the demonstrated specificity of the HPLC method with respect to potential interference from digoxin metabolites, endogenous digoxin-like immunoactive substances, and coadministered drugs and their metabolites, allows quantitation of the degree of interference in digoxin immunoassays under actual therapeutic drug monitoring conditions. Clinically significant interferences (0.3 to 1.1 ng/ml) with immunoassay determination were found in the majority of patients in all three diseases studied.

Vasodilatory state of decompensated cirrhosis: relation to hepatic dysfunction, ascites, and vasoactive substances

The objective of this study was to determine the relations between the hallmark circulatory finding of decompensated cirrhosis, a reduced systemic vascular resistance (SVR), and the indices of hepatic decompensation, the accumulation of ascites, and the concentrations of various vasoactive substances. At a university-affiliated teaching hospital, eighteen hospitalized patients with cirrhosis and 18 age- and sex-matched healthy subjects were used. This was a case-control study. Measurements included cardiac dimensions and indices derived from echocardiograms and Doppler studies, abdominal ultrasound estimates of ascites, indices of hepatic function, and various serum (S) and urinary (U) substances. Results showed that cirrhotics had increased left atrial and left ventricular dimensions, left ventricular mass, heart rate, cardiac output (CO), transvalvular velocities, and a decreased SVR. SVR was related to hepatic dysfunction, as reflected by an abnormal prothrombin time ratio (r = -0.64, p = 0.006), and also related to overall severity of liver disease as estimated by the Child-Pugh score (r = -0.53, p = 0.044). Although cirrhotics with ascites generally had a reduced SVR, estimates of ascites were directly related to SVR (r = 0.57, p = 0.03) and inversely related to CO (r = -0.53, p = 0.04). Concentrations of S and U digoxin-like immunoreactive substance (DLIS) were also increased, but the concentrations of S glucagon and estradiol were not elevated. The accumulations of S and U DLIS, S glucagon, and S estradiol were all related to hepatic dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of a relation between urinary digoxin-like immunoreactive substance and cardiac performance

OBJECTIVE

To determine the relation between urinary digoxin-like immunoreactive substance (DLIS) and cardiac performance.

DESIGN

Cohort study.

SETTING

Echocardiography laboratory of a university-affiliated teaching hospital.

SUBJECTS

Thirty-four individuals referred for echocardiographic studies who had never received cardiac glycosides or other substances known to cross-react with a digoxin radioimmunoassay and had no condition that has been associated with increased DLIS.

MEASUREMENTS

Cardiac dimensions and indices of cardiac performance derived from echocardiograms and cardiac Doppler flow studies and concentrations of urinary DLIS, creatinine, and electrolytes.

RESULTS

Urinary DLIS ranged from < 0.125 ng (digoxin equivalents) per milliliter (below the sensitivity of the assay) to 0.99 ng/ml, averaging 0.22 +/- 0.24 ng/ml. On bivariate analyses, UDLIS was found to correlate significantly with body weight, left ventricular (LV) end-diastolic dimension, LV fractional shortening, mitral transvalvular flow velocity following atrial systole, and urinary calcium. On multivariate analyses, the association between urinary DLIS (alone or adjusted for urinary creatinine) and LV fractional shortening emerged as the paramount independent relation.

CONCLUSION

Urinary DLIS can be related to cardiac performance under steady-state conditions. This suggests that DLIS may be a ligand for a cardiac glycoside receptor.

Plasma levels of brain natriuretic peptide in patients with cirrhosis

Plasma levels of brain natriuretic peptide, a recently identified cardiac hormone with natriuretic activity, were measured in 11 healthy subjects, 13 cirrhotic patients without ascites, 18 nonazotemic cirrhotic patients with ascites and 6 patients with cirrhosis, ascites and functional kidney failure. Plasma levels of brain natriuretic peptide were similar in healthy subjects and cirrhotic patients without ascites (5.56 +/- 0.65 and 7.66 +/- 0.68 fmol/ml, respectively). In contrast, cirrhotic patients with ascites, with and without functional kidney failure, had significantly higher plasma concentrations of brain natriuretic peptide (19.56 +/- 1.37 and 16.00 +/- 1.91 fmol/ml, respectively) than did healthy subjects and patients without ascites (p less than 0.01); no significant difference was found between the two groups of cirrhotic patients with ascites with respect to this parameter. In the whole group of cirrhotic patients included in the study, brain natriuretic peptide level was directly correlated with the degree of impairment of liver and kidney function, plasma renin activity and plasma levels of aldosterone and atrial natriuretic peptide. The results of this study indicate that brain natriuretic peptide is increased in cirrhotic patients with ascites and suggest that sodium retention in cirrhosis is not due to deficiency of this novel cardiac hormone.

Digoxin-like immunoreactivity: is it still worth measuring?

On the assumption that digoxin-like immunoreactivity may represent digitalis-like sodium pump inhibitors in the mammalian body, many investigators have used radioimmunoassay for digoxin to monitor such factors during the past decade. The presence of digoxin-like immunoreactivity has been confirmed by numerous studies using biochemical, immunological or morphological methods. Very recently, ouabain or a very similar substance, which did not cross-react with antidigoxin antibodies, was identified from the human plasma as the long-sought sodium pump inhibitor. However, it is yet to be determined whether sodium pump inhibitory activity in the circulation results from one substance or several. Some researchers still insist on the possible physiological roles of digoxin-like immunoreactivity which may or may not be related to the regulation of sodium pump. These issues are critically reviewed in this article.

Natriuretic hormone activity in the urine of cirrhotic patients

The ability of urine extracts to inhibit sodium and potassium-activated ATPase, cross-react with antidigoxin antibodies and induce natriuresis in rats was investigated in 10 healthy subjects, 10 cirrhotic patients without ascites (compensated cirrhotics), 27 nonazotemic cirrhotic patients with ascites and 10 cirrhotic patients with ascites and functional renal failure to assess whether reduced activity of natriuretic hormone contributes to sodium retention in cirrhosis. No significant differences were seen between healthy subjects and compensated cirrhotic patients in any of these parameters (sodium and potassium-activated ATPase inhibition = 178.5 +/- 19.8 vs. 247.4 +/- 48.7 nmol equivalent of ouabain/day; digoxinlike activity = 43.9 +/- 6.1 vs. 48.0 +/- 5.6 ng equivalent of digoxin/day; natriuretic activity = 0.36 +/- 0.15 vs. 0.63 +/- 0.27 mumol/min). Cirrhotic patients with ascites with and without functional renal failure showed significantly higher values of sodium and potassium-activated ATPase inhibition (708.1 +/- 94.0 and 529.2 +/- 53.9 nmol equivalent of ouabain/day, respectively), digoxinlike activity (136.9 +/- 7.2 and 116.3 +/- 7.9 ng equivalent of digoxin/day) and natriuretic activity (1.78 +/- 0.48 and 1.93 +/- 0.37 mumol/min) than healthy subjects and compensated cirrhotic patients. We saw no significant differences between these two groups of cirrhotic patients with ascites with respect to these parameters. In the cirrhotic patients studied, sodium and potassium-activated ATPase inhibition and antidigoxin antibodies directly correlated with the degree of impairment of hepatic and renal function, plasma renin activity and plasma levels of aldosterone and norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)