Ethylene glycol toxicity: the role of serum glycolic acid in hemodialysis

OBJECTIVE

To correlate serum glycolic acid levels with clinical severity and outcome in ethylene glycol poisoning and to determine if glycolic acid levels are predictive of renal failure and the need for hemodialysis.

METHODS

We measured serum ethylene glycol and glycolic acid levels by gas chromatography/mass spectrometry for 41 admissions (39 patients) for ethylene glycol ingestion and performed retrospective chart reviews.

RESULTS

Eight patients died, all of whom developed acute renal failure. Of the survivors, 15 also developed acute renal failure, whereas 18 did not. Of those with normal renal function, 8 had glycolic acid levels below detection limits (< 0.13 mmol/L) despite ethylene glycol levels as high as 710 mg/dL; 7 of these patients coingested ethanol. Pertinent initial laboratory data for each group are as follows (mean; range): Deceased: pH 6.99 (6.82-7.22); bicarbonate, 4.8 mmol/L (2-9); anion gap, 28.6 mmol/L (24-40); glycolic acid, 23.5 mmol/L (13.8-38.0); ethylene glycol, 136.5 mg/dL (6-272). Survived/acute renal failure: pH 7.07 (6.75-7.32); bicarbonate, 5.6 mmol/L (1-12); anion gap, 28.7 mmol/L (18-41); glycolic acid, 20.2 mmol/L (10.0-30.0); ethylene glycol, 238.8 mg/dL (12-810). No acute renal failure with glycolic acid > 1.0 mmol/L: pH 7.29 (7.12-7.46); bicarbonate, 14.7 mmol/L (4-23); anion gap, 16.5 mmol/L (10-26); glycolic acid, 6.8 mmol/L (2.6-17.0); ethylene glycol, 269.1 mg/dL (6-675). No acute renal failure with glycolic acid < 1.0 mmol/L: pH 7.41 (7.38-7.47); bicarbonate, 23.4 mmol/L (17-25); anion gap, 11.8 mmol/L (8-18); glycolic acid, 0.1 mmol/L (0-0.66); ethylene glycol, 211 mg/dL (8-710). The mean time postingestion to admission generally correlated with severity as follows: deceased, > or = 10.4 h; survived/acute renal failure, > or = 9.9 h; no acute renal failure with glycolic acid > 1.0 mmol/L, > or = 6.2 h; no acute renal failure with glycolic acid < 1.0 mmol/L, > or = 3.7 h. Hematuria was more prevalent than oxaluria (86% and 41%, respectively), but neither was individually predictive of acute renal failure. Good correlations were found between glycolic acid levels and anion gap (r2 = 0.7724), pH (r2 = 0.7921), and bicarbonate (r2 = 0.6579); poor correlations (r2 < 0.0023) occurred between ethylene glycol levels and glycolic acid, pH, anion gap, and bicarbonate. Measured ethylene glycol values were highly correlated with ethylene glycol values calculated from the osmolal gap (r2 = 0.9339), but the latter overestimates the true value by about 7%, on average. An initial glycolic acid level > or = 10 mmol/L predicts acute renal failure with a sensitivity of 100%, a specificity of 94.4%, and an efficiency of 97.6%. Ethylene glycol levels are not predictive of acute renal failure or central nervous system manifestations of toxicity. If only ethylene glycol values are available (measured or calculated), an initial anion gap > 20 mmol/L is 95.6% sensitive and 94.4% specific for acute renal failure when ethylene glycol is present. Likewise, initial pH < 7.30 is 100% sensitive and 88.5% specific for acute renal failure.

CONCLUSION

We propose glycolic acid > 8 mmol/L as a criterion for the initiation of hemodialysis in ethylene glycol ingestion. Patients with glycolic acid < 8 mmol/L probably do not need dialysis, regardless of the ethylene glycol concentration, when metabolism of ethylene glycol is therapeutically inhibited. In the absence of glycolic acid values, an anion gap > 20 mmol/L or pH < 7.30 predicts acute renal failure.

Simultaneous determination of ethylene glycol and glycolic acid in serum by gas chromatography-mass spectrometry

We describe a gas chromatographic-mass spectrometric (GC-MS) procedure for the simultaneous determination of ethylene glycol (EG) and its major toxic metabolite, glycolic acid (GA), in serum. In this method, serum (50 microL) is treated with 150 microL of glacial acetic acid/acetonitrile (1:10, v/v; contains internal standard, 1,3-propanediol, 15 mg/dL) to precipitate protein. After centrifugation, 10 microL of supernate is treated with 500 microL of 2,2-dimethoxypropane/dimethylformamide (80:20, v/v) to convert water to methanol, and the volume is then reduced to < 100 microL of dimethylformamide (but not to dryness). After formation of tertbutyldimethylsilyl derivatives, analysis is performed by capillary column GC-MS in selected ion mode. The method gives a linear response to 1000 mg/L each EG and GA (16.1 mmol/L and 13.2 mmol/L, respectively) and has a lower limit of detection and a lower limit of quantitation of 10 mg/L each EG and GA (0.16 mmol/L and 0.13 mmol/L, respectively). Total assay imprecision is CV < or = 6.4% (200 and 800 mg/L EG and GA [3.2 and 12.9 mmol/L EG; 2.6 and 10.5 mmol/L GA, respectively]). Absolute recovery from human serum was 91.1% for EG and 77.6% for GA. The procedure is free from any known interference. A complete analysis set (three calibrators, patient serum neat, patient serum diluted 1:5 (v/v), and two controls) may be completed in about 2 h. A preliminary result, based on a single calibrator and patient serum diluted 1:5 (v/v), is complete in about 1 h. The method has been used to aid the diagnosis and management in 34 cases of EG intoxication. Selected cases are briefly reviewed.

Urinary concentrations of the soluble adhesion molecule E-cadherin and total protein in patients with bladder cancer

Reduced expression of the adhesion molecule E-cadherin has been associated with increased invasiveness and poorer survival in patients with bladder cancer. We have examined soluble E-cadherin (sE-cadherin) and total protein concentrations in urine from patients with bladder cancer (n = 34), non-neoplastic benign urological diseases (n = 14) and healthy controls (n = 21) to determine their diagnostic and prognostic significance. Soluble E-cadherin concentrations of the cancer group were significantly higher (P < 0.001) than those of the controls but the benign group was not significantly different from either the cancer group or the controls. When sE-cadherin concentrations were adjusted for creatinine, similar but more statistically significant results were obtained and the benign group was significantly elevated compared with the controls (P < 0.01). No differences were apparent between the invasive (pT1-4) and non-invasive (pTa) cancers. Urinary total protein concentrations in the cancer group were significantly higher than the controls (P < 0.001) and the benign group (P < 0.05) although no difference was seen between the benign group and patients with non-invasive (pTa) cancer or between the benign group and controls. When expressed as the protein/creatinine index, results were similar but more statistically significant and a significant difference was seen between invasive and non-invasive cancers (P < 0.01). Only the protein/creatinine index correlated significantly with stage of the tumour (P < 0.01). It is concluded that urinary sE-cadherin measurements are of no greater value than urinary total protein.

Urolithiasis associated with the protease inhibitor indinavir

OBJECTIVES

To report the association between the protease inhibitor indinavir and the development of urolithiasis.

METHODS

Case reports of three adult patients infected with the human immunodeficiency virus who developed surgical renal stones while being treated with indinavir are presented.

RESULTS

Of the 3 patients requiring surgical intervention, stone analyses were available in 2. One stone revealed an inner core of an unidentifiable crystal surrounded by calcium oxalate, and another was found to have indinavir components as determined by thin-layer chromatography and gas chromatography-mass spectrometry. Metabolic evaluation of all 3 patients identified significant hypocitraturia as an isolated finding.

CONCLUSIONS

The widely used protease inhibitor indinavir is associated with the development of urolithiasis and may act as a nidus for heterogeneous nucleation leading to the development of mixed urinary stones. Surgical intervention may be necessary in some cases. Underlying metabolic abnormalities may contribute to the increased incidence of stone formation. Urologists and other health care providers should be aware of this association, as combined medical and surgical intervention may be necessary.

Laboratory and clinical evaluation of assays for beta-hydroxybutyrate

We have performed a two-part evaluation of assays for beta-hydroxybutyrate (beta HB). In Part I, we evaluated the analytical acceptability of a dry film, self-contained analyzer for beta HB measurement (KetoSite; GDS Diagnostics, Elkhart, Ind). The assay response is linear and between-day imprecision is acceptable. Acetoacetate (AcAc) interferes severely with this assay. This interference could be minimized by dilution of serum before the assay. With this predilution protocol, KetoSite beta HB results compare favorably with an automated Sigma (St. Louis, Mo) beta HB assay. In Part II, we compared the clinical utility of beta HB measurements (Sigma) with the qualitative measurement of ketones using the nitroprusside test (Acetest; Bayer, Elkhart, Ind) for the diagnosis and management of diabetic ketoacidosis (DKA). Test results for both assays were abnormal for all patients with DKA on admission. However, frequent monitoring with either test during the management of uncomplicated DKA added little if any additional clinical information over routine measurements of serum glucose and total carbon dioxide.

Simultaneous determination of ethylene glycol and its major toxic metabolite, glycolic acid, in serum by gas chromatography

We developed a gas-chromatographic procedure for the simultaneous determination of ethylene glycol (EG) and its major toxic metabolite, glycolic acid (GA), suitable for clinical use in instances of EG intoxication. After serum protein precipitation with acetonitrile (containing internal standard), the supernate is treated with 2,2-dimethoxypropane (containing dimethylformamide) to remove water, and the volume is then reduced by evaporation to &lt;100 microL of dimethylformamide (but not to dryness). After trimethylsilyl derivatization, the resulting derivatives are analyzed by capillary column gas chromatography. Only 100 microL of serum is required and the entire determination, including calibrators and controls, takes &lt;2 h. The method gives a linear response to at least 10 g/L EG and 5 g/L GA and has a limit of detection &lt;10 mg/L. Intraassay CV is &lt; or = 2.8% for EG (100 and 1000 mg/L) and GA (100 and 500 mg/L); between-day CV is &lt; or = 6.5%. The absolute recovery from serum was 91% for EG and 77-82% for GA (200 and 2000 mg/L each). Relative to calibrators prepared bovine serum albumin (70 g/L), the recovery was 99-104% for EG (100 - 5000 mg/L) and 95-105% for GA (50 - 2500 mg/L). No clinically important interference was detected for &gt;60 exogenous or endogenous compounds and drugs.

Simultaneous determination of ethylene glycol and its major toxic metabolite, glycolic acid, in serum by gas chromatography

We developed a gas-chromatographic procedure for the simultaneous determination of ethylene glycol (EG) and its major toxic metabolite, glycolic acid (GA), suitable for clinical use in instances of EG intoxication. After serum protein precipitation with acetonitrile (containing internal standard), the supernate is treated with 2,2-dimethoxypropane (containing dimethylformamide) to remove water, and the volume is then reduced by evaporation to <100 microL of dimethylformamide (but not to dryness). After trimethylsilyl derivatization, the resulting derivatives are analyzed by capillary column gas chromatography. Only 100 microL of serum is required and the entire determination, including calibrators and controls, takes <2 h. The method gives a linear response to at least 10 g/L EG and 5 g/L GA and has a limit of detection <10 mg/L. Intraassay CV is < or = 2.8% for EG (100 and 1000 mg/L) and GA (100 and 500 mg/L); between-day CV is < or = 6.5%. The absolute recovery from serum was 91% for EG and 77-82% for GA (200 and 2000 mg/L each). Relative to calibrators prepared bovine serum albumin (70 g/L), the recovery was 99-104% for EG (100 - 5000 mg/L) and 95-105% for GA (50 - 2500 mg/L). No clinically important interference was detected for >60 exogenous or endogenous compounds and drugs.

Soluble forms of the adhesion molecule E-cadherin in urine

The adhesion molecule E-cadherin is essential for maintaining epithelial intercellular adhesion. Loss or reduced expression of E-cadherin has been related to invasive behaviour in a wide range of carcinomas. Using immunoblotting techniques, the existence of multiple soluble forms of E-cadherin was demonstrated in urine from healthy volunteers and patients with benign urinary tract disorders or bladder cancer. The existence of soluble forms of E-cadherin in the urine may reflect shedding from the urinary tract epithelium as part of the normal turnover of this molecule. The possibility that enhanced shedding may contribute to the loss of E-cadherin expression/function in malignancy is discussed.

Measurement of serum isopropanol and the acetone metabolite by proton nuclear magnetic resonance: application to pharmacokinetic evaluation in a simulated overdose model

The purpose of this investigation was to 1) compare the performance of proton nuclear magnetic resonance spectroscopy to gas chromatography head-space analysis in the measurement of serum isopropanol and its metabolite, acetone, obtained during a simulated overdose, and 2) compare pharmacokinetic parameters obtained using the two analytical techniques. Three healthy volunteers ingested 0.6 mL/kg of 70% isopropanol and blood samples were obtained at baseline, 0.16, 0.33, 0.66, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12.0, and 24.0 hours post-ingestion. Resulting sera were analyzed by gas chromatography head-space analysis and proton nuclear magnetic resonance spectroscopy for determination of isopropanol and acetone concentrations. A correlation between concentrations quantitated by gas chromatography head-space analysis versus proton nuclear magnetic resonance spectroscopy was determined using linear regression. Pharmacokinetic disposition parameters were determined from serum concentration-time data and compared using analysis of variance. For isopropanol, the linear regression equation which describes the relationship between gas chromatography head-space analysis and proton nuclear magnetic resonance spectroscopy was y = 1.041x - 2.180 (r2 = 0.995, p < 0.0001); for acetone, y = 1.022x - 0.946 (r2 = 0.984, p < 0.0001). Pharmacokinetic disposition parameters derived from the two analytical methods were comparable. Proton nuclear magnetic resonance spectroscopy can be used to rapidly quantitate serum isopropanol and acetone concentrations in the same sample when gas chromatography head-space analysis is unavailable. Also, proton nuclear magnetic resonance spectroscopy can be used to follow serial serum concentrations during an ingestion for the purpose of pharmacokinetic analysis.

Influence of serum separator tubes on total and free phenytoin concentrations and dosages

The influence of serum separator tubes (SSTs) on total and free phenytoin concentrations and phenytoin dosages was evaluated in patients treated with phenytoin. Thirty blood samples were obtained from 18 patients. Equal volumes of blood were placed into SSTs and plain tubes. Samples were centrifuged, and serum analyzed for total and free phenytoin by fluorescence polarization immunoassay (FPIA) at 2, 24, and 48 h. Total phenytoin concentrations collected in SSTs were significantly lower than those collected in plain tubes at 2 (12.3 vs 12.8 mg/L, p < 0.01), 24 (11.4 vs 12.9 mg/L, p < 0.01), and 48 h (10.9 vs 12.9 mg/L, p < 0.01). These differences resulted in significantly higher calculated maximum rates of metabolism (Vmax) and daily phenytoin dosages (R0) for SSTs at 24 (Vmax: 10.4 vs 10.1 mg/kg/day; R0: 8.2 vs 8.0 mg/kg/day, p < 0.01) and 48 h (Vmax: 10.8 vs 10.3 mg/kg/day; R0: 8.5 vs 8.1 mg/kg/day, p < 0.01). Free phenytoin concentrations from SSTs were significantly lower at 48 h (1.56 vs 1.61 mg/L, p < 0.05). However, there were no significant differences in calculated dosages. Observed statistical differences in total phenytoin concentrations can be clinically important for making dosage adjustments, especially in patients undergoing nonlinear elimination. Thus, SSTs should not be used to collect blood for total serum phenytoin determination.

High-resolution proton nuclear magnetic resonance spectroscopy in the detection of low molecular weight volatiles

Proton nuclear magnetic resonance spectroscopy (1H MRS) has been used to identify ethanol in vivo and to detect other exogenous low molecular weight volatiles in human serum. 1H MRS was used to detect and quantitate 15 human sera containing various concentrations and combinations of ethanol, isopropanol, acetone, and methanol as previously quantitated by headspace gas chromatography. The 1H MRS method was linear for each alcohol. The lowest detectable alcohol concentration was 15 mg/L (peak height equal to three times the signal-to-noise ratio), and 30 mg/L (+/- 10% relative standard deviation) was the lowest level reproducibly quantitated. Within-run and day-to-day coefficients of variation (CV) ranged from 0.8 to 2.0% and 0.9 to 1.2%, respectively, for methanol; 0.5 to 1.9% and 0.6 to 1.3% for acetone; and 0.5 to 1.6% and 0.3 to 2.2% for isopropanol. In all cases, the lowest CVs for a particular compound were obtained for the highest measured concentration (1500 mg/L), and the highest CVs were observed for the lowest concentration (250 mg/L). The 1H MRS method for detection of these volatiles does not require sample pretreatment and is nondestructive, which allows for further analysis by other methods.

High-resolution proton nuclear magnetic resonance spectroscopy in the detection and quantitation of ethanol in human serum

A precise, accurate, and nondestructive method for the detection and quantitation of serum ethanol in humans using proton (1H) nuclear magnetic resonance spectroscopy (MRS) was developed. The 1H MRS method was linear within the range of 30-1500 mg/L. The lowest detectable ethanol concentration was 15 mg/L, with 30 mg/L being the lowest level reproducibly quantitated. Within-run and day-to-day coefficients of variation (CV) ranged from 0.6 to 2.7% and 0.5 to 3.5%, respectively. The excellent day-to-day CVs indicate a negligible loss of ethanol due to volatilization during analysis. Fifteen human serum samples found to be negative for ethanol by headspace gas chromatography (HSGC) had no ethanol as detected by 1H MRS. Twenty-eight human serum samples with ethanol concentrations (determined by HSGC) ranging from 370 to 4440 mg/L were accurately reproduced by 1H MRS. The 1H MRS method required no pretreatment and was nondestructive, thereby allowing for further analysis by confirmatory methods.

Severe phenytoin intoxication as a result of altered protein binding in AIDS

Alterations in plasma protein binding may alter patient response to pharmaceutical agents because only free drug is considered to be pharmacologically active. Such alterations appear to be more significant with highly bound agents such as phenytoin. Traditionally, most drug assays monitor total drug concentrations and do not quantitate free drug. When binding alterations are present, total drug concentrations may mislead clinicians in evaluating patient response. We describe a case in which profound hypoalbuminemia (0.2 g/dL), associated with focal segmental glomerulosclerosis, produced toxic free phenytoin concentrations (4.9 micrograms/mL) in an HIV-positive 25-year-old black woman. At such a high serum concentration of free phenytoin, the patient exhibited seizure-like effects. Renal abnormalities and hypoalbuminemia associated with acquired immunodeficiency syndrome (AIDS) may place patients at risk for elevated free fractions of phenytoin and subsequent toxicity.

Evaluation of precision and accuracy of a fluorescence polarization immunoassay system after dilution of serum samples containing fluorescein dye

The accuracy and precision of a fluorescence polarization immunoassay for diluted gentamicin serum samples in the presence of fluorescein dye is described.

Pentobarbital pharmacokinetics in patients with severe head injury

Intravenous administration of high-dose pentobarbital has been proposed as a treatment for elevated intracranial pressure refractory to other measures in brain-injured patients. The purpose of this clinical study was to examine the pharmacokinetics of high-dose continuous intravenous infusion of pentobarbital in this critical care setting. Six patients received a 25-34 mg/kg intravenous loading dose followed by a 1-3 mg/kg/h continuous infusion for 61-190 hours. Dosing rates were adjusted based on the patient's clinical status. The mean clearance was 0.72 ml/min/kg, with a volume of distribution (Vd) of 1.03 L/kg and a terminal half-life of 19.1 h. Considerable variation in individual patient parameters was observed. In addition, a change in clearance was suggested in patients requiring a longer infusion duration.

Simplified high performance liquid chromatographic method for the determination of clonazepam and other benzodiazepines in serum

A convenient and sensitive high performance liquid chromatographic method was developed for determination of clonazepam in serum using a C-18 reverse-phase column, and mobile phase consisting of a 50:35:15 mixture by volume of pH 6.0 phosphate buffer:methanol:acetonitrile. Quantitation was performed at 313 nm with flunitrazepam as the internal standard. Using 1 ml of serum for extraction, the assay is linear for clonazepam concentrations between 10 and 250 ng/ml. The relative recovery averaged 100.3%, and the coefficient of variation for between-day and within-day assays was less than 7%. A simple modification permits analysis of 200 microliter of serum, with little loss of precision and with a detection limit of 20 ng/ml. Only three drugs tested (nitrazepam, methaqualone, and norchlordiazepoxide) interfered with the assay, and none are likely to be used therapeutically with clonazepam. Importantly, carbamazepine and carbamazepine-10,11-epoxide do not interfere under the conditions of the assay. The method is equally suitable for the determination of nitrazepam. By adjusting the mobile phase so that volume ratios of phosphate buffer, methanol, and acetonitrile are 45:35:20, and using nitrazepam as the internal standard, seven other benzodiazepines (demoxepam, oxazepam, chlordiazepoxide, norchlordiazepoxide, temazepam, diazepam, and nordiazepam) can be resolved at 254 nm.

Measurement of alpha-glucosidase activity in serum from patients with cystic fibrosis or pancreatitis

We measured the activity of a non-lysosomal alpha-glucosidase with pH optimum near 6.0 in serum from a wide variety of patients, using the fluorogenic substrate, 4-methylumbelliferyl-alpha-D-glucopyranoside. Acutely ill patients with cystic fibrosis (CF) demonstrated significant increases in alpha-glucosidase compared with CF outpatients. The former group of CF patients experienced far more severe chronic pulmonary disease than did the latter, whereas both groups had similar degrees of gastrointestinal impairment. Patients with pancreatitis associated with trauma or complicated by severe necrosis, hemorrhage, or abscess also displayed greater increases in alpha-glucosidase than did patients with uncomplicated (edematous) pancreatitis. For CF outpatients and patients with either edematous pancreatitis or pancreatic cancer, the alpha-glucosidase activity was similar to that for the general hospital-patient population. Corresponding changes were not observed for other measured serum glycosidases (alpha-fucosidase, alpha-mannosidase, beta-glucuronidase, beta-N-acetylglucosaminidase). Measurement of serum alpha-glucosidase may be of value in assessing the clinical course in CF and in differentiating necrotizing from edematous pancreatitis.

Measurement of alpha-glucosidase activity in serum from patients with cystic fibrosis or pancreatitis

We measured the activity of a non-lysosomal alpha-glucosidase with pH optimum near 6.0 in serum from a wide variety of patients, using the fluorogenic substrate, 4-methylumbelliferyl-alpha-D-glucopyranoside. Acutely ill patients with cystic fibrosis (CF) demonstrated significant increases in alpha-glucosidase compared with CF outpatients. The former group of CF patients experienced far more severe chronic pulmonary disease than did the latter, whereas both groups had similar degrees of gastrointestinal impairment. Patients with pancreatitis associated with trauma or complicated by severe necrosis, hemorrhage, or abscess also displayed greater increases in alpha-glucosidase than did patients with uncomplicated (edematous) pancreatitis. For CF outpatients and patients with either edematous pancreatitis or pancreatic cancer, the alpha-glucosidase activity was similar to that for the general hospital-patient population. Corresponding changes were not observed for other measured serum glycosidases (alpha-fucosidase, alpha-mannosidase, beta-glucuronidase, beta-N-acetylglucosaminidase). Measurement of serum alpha-glucosidase may be of value in assessing the clinical course in CF and in differentiating necrotizing from edematous pancreatitis.

Effect of protein concentration on the determination of digoxin in serum by fluorescence polarization immunoassay

Determination of digoxin by fluorescence polarization immunoassay (FPIA) with the Abbott "TDx" is significantly influenced by the concentration of total serum protein. Each 10 g/L increase in serum protein results in an 8% decrease in measured digoxin. Studies with [3H]digoxin confirmed that digoxin binds to the protein pellet during the trichloroacetic acid precipitation step before the immunoassay. Serum protein, or equal concentrations of albumin or gamma-globulin, exert an equivalent effect on the apparent digoxin value. Because the total protein concentration of the assay calibrators is low (50 g/L) compared with its reference interval in serum (60-80 g/L), results by FPIA may be expected to be low by an average of 16% (range, 8-24%). Digoxin results by FPIA will be most nearly accurate when the calibrators include a total protein concentration of about 70 g/L. Patients' specimens with abnormally high or low protein content will give falsely high or low results for digoxin.

Effect of protein concentration on the determination of digoxin in serum by fluorescence polarization immunoassay

Determination of digoxin by fluorescence polarization immunoassay (FPIA) with the Abbott "TDx" is significantly influenced by the concentration of total serum protein. Each 10 g/L increase in serum protein results in an 8% decrease in measured digoxin. Studies with [3H]digoxin confirmed that digoxin binds to the protein pellet during the trichloroacetic acid precipitation step before the immunoassay. Serum protein, or equal concentrations of albumin or gamma-globulin, exert an equivalent effect on the apparent digoxin value. Because the total protein concentration of the assay calibrators is low (50 g/L) compared with its reference interval in serum (60-80 g/L), results by FPIA may be expected to be low by an average of 16% (range, 8-24%). Digoxin results by FPIA will be most nearly accurate when the calibrators include a total protein concentration of about 70 g/L. Patients' specimens with abnormally high or low protein content will give falsely high or low results for digoxin.

Gas-chromatographic determination of ethylene glycol in serum

We describe a new gas-chromatographic procedure for ethylene glycol in serum, determined as the cyclic phenylboronate ester. The method is rapid, requires only 100 microL of serum, and either an OV-1 or an OV-17 column is used. The linear dynamic range extends to at least 5000 mg/L, with a lower limit of detection of 10 mg/L. Analytical recovery of ethylene glycol from serum averaged 97% (95-101%) over the concentration range of 250-5000 mg/L. The method demonstrates good precision, with CVs less than 2.5%, over the concentration range 500-2000 mg/L.

Gas-chromatographic determination of ethylene glycol in serum

We describe a new gas-chromatographic procedure for ethylene glycol in serum, determined as the cyclic phenylboronate ester. The method is rapid, requires only 100 microL of serum, and either an OV-1 or an OV-17 column is used. The linear dynamic range extends to at least 5000 mg/L, with a lower limit of detection of 10 mg/L. Analytical recovery of ethylene glycol from serum averaged 97% (95-101%) over the concentration range of 250-5000 mg/L. The method demonstrates good precision, with CVs less than 2.5%, over the concentration range 500-2000 mg/L.

Enzyme-coupled ultraviolet determination of alpha-amylase activity with the GEMSAEC centrifugal analyzer

We evaluated the Harleco alpha-glucosidase/hexokinase/glucose-6-phosphate dehydrogenase-coupled alpha-amylase method, bu use of the GEMSAEC centrifugal analyzer. Performance evaluation included kinetic studies of substrate and maltose hydrolysis as well as effects of endogenous glucose and fructose. The reagent was found to give a linear response with alpha-amylase activity to greater than 1200 U/liter. Within-run precision resulted in coefficients of variation (CV) of 0.9 to 3.2% over the range studied. Day-to-day precision corresponded to CV's of 2.4 to 4.4% over the same range of alpha-amylase procedure was found to be good (r = 0.997) for patients' sera examined.

Enzyme-coupled ultraviolet determination of alpha-amylase activity with the GEMSAEC centrifugal analyzer

We evaluated the Harleco alpha-glucosidase/hexokinase/glucose-6-phosphate dehydrogenase-coupled alpha-amylase method, bu use of the GEMSAEC centrifugal analyzer. Performance evaluation included kinetic studies of substrate and maltose hydrolysis as well as effects of endogenous glucose and fructose. The reagent was found to give a linear response with alpha-amylase activity to greater than 1200 U/liter. Within-run precision resulted in coefficients of variation (CV) of 0.9 to 3.2% over the range studied. Day-to-day precision corresponded to CV's of 2.4 to 4.4% over the same range of alpha-amylase procedure was found to be good (r = 0.997) for patients' sera examined.

Hemoglobin interference with Du Pont Automatic Clinical Analyzer procedure for calcium

Hemoglobin in concentrations of approximately 2.5 g/liter or greater significantly increases values for apparent calcium in serum as determined with the Du Pont aca, an interference attributable to the 575-nm absorption band of oxyhemoglobin being uncompensated by the 577--600 nm differential absorption reading of the calcium o-cresolphthalein complexone complex.

Hemoglobin interference with Du Pont Automatic Clinical Analyzer procedure for calcium

Hemoglobin in concentrations of approximately 2.5 g/liter or greater significantly increases values for apparent calcium in serum as determined with the Du Pont aca, an interference attributable to the 575-nm absorption band of oxyhemoglobin being uncompensated by the 577--600 nm differential absorption reading of the calcium o-cresolphthalein complexone complex.