Establishment and evaluation of a new chemiluminescent enzyme immunoassay for carcinoembryonic antigen adapted to the fully automated ACCESS system

We have established a new chemiluminescent enzyme immunoassay for carcinoembryonic antigen (CEA), designated ACCESS CEA, which is adapted to the fully automated ACCESS immunoassay analyzer. The assay is based on a one step sandwich-type method using two monoclonal antibodies, one of which is immobilized on micrometer-size paramagnetic particles and the other is conjugated to alkaline phosphatase. Ten microliters of calibrators or sera are incubated for 5 minutes at 37 degrees C with the particles and with the alkaline phosphatase conjugate. The particles are then magnetically separated and washed to remove unbound components. Time needed to obtain the first result is less than 15 minutes. The assay range was 0.04-1000 micrograms/l of CEA, and the possible high-dose hook effect was prevented at CEA concentrations up to 100000 micrograms/l in this working range. The coefficient of variation (CV) for intra-assay precision was 3.0 to 4.7%, and inter-assay CV was 3.4 to 5.6%. The sample carryover was less than 0.001%. The analytical recovery ranged from 98 to 104% and a dilution linearity was demonstrated. No interference was detected in any sample with levels up to 300 mg/l for bilirubin, 12000 mg/l for haemoglobin, 50000 mg/l for human serum albumin, 8500 mg/l for triacylglycerol, and 500000 IU/l for rheumatoid factor. The ACCESS CEA assay also showed very homogeneous reactivity with purified CEA preparations from different tumours and could discriminate CEA from four CEA-related normal antigens tested. Serum samples (n = 362) from patients with malignant or non-malignant disease, as well as from healthy individuals, were analyzed by the ACCESS CEA assay and by the established IMx CEA assay. The CEA values determined by the ACCESS CEA assay were in good agreement with those determined by the IMx CEA assay, and the ACCESS CEA assay significantly increased the sensitivity and specificity of tumour diagnosis as compared with the IMx CEA assay.     

Lipid interference in the determination of the concentration of haemoglobin in plasma using the ACA SX analyzer

In comparison to a triple wavelength procedure, the dual wavelength method for the determination of plasma haemoglobin concentration using the ACA analyzer showed considerable interference with hypertriglyceridaemic (triacylglycerols > 2.3 mmol/l) plasma. By addition of isolated human lipoprotein fractions to normotriglyceridaemic plasma, chylomicrons were identified as a major source of interference with the ACA plasma haemoglobin method, whereas VLDL was without effect up to a triacylglycerol concentration of 5.7 mmol/l. Airfuge ultracentrifugation proved to be a reliable means for removal of interfering lipid. We conclude that the extent of lipid interference with the ACA plasma haemoglobin method is highly dependent on the type of lipoprotein present. An accurate measurement of plasma haemoglobin concentrations in non-fasting plasma can only be ensured after lipid removal through airfuge ultracentrifugation.     

Quantitative automated particle-enhanced immunonephelometric assay for the routinary measurement of human cystatin C

Human cystatin C is a low molecular mass protein of 13359 Dalton recently proposed as a new very sensitive marker of changes in glomerular filtration rate. Serum cystatin C concentration correlates negatively with glomerular filtration rate as well as or better than creatinine. We evaluated a recently introduced automated nephelometric immunoassay for cystatin C in serum or EDTA-plasma samples on the Behring Nephelometer System. The assay consists of incubating the 100-fold diluted sample for 6 minutes with latex particles covalently coated with anti-human cystatin C antibodies, and then quantifying the change of light-scatter produced. Method reproducibility is satisfactory, the intra- and inter-assay coefficients of variation ranging from 1.58% to 3.77% and from 5.6% to 11.47% respectively. Rheumatoid factor (< or = 1116 IU/ml), bilirubin (< or = 418 micrommol/l), triglycerides (10.47 mmol/), and haemoglobin (12 g/l) do not significantly interfere in the assay. No significant difference was found in cystatin C concentration between serum and EDTA-plasma samples. Cystatin C is stable in serum samples stored under different conditions up to one month. This method correlates well (mean difference=-0.536+/-0.307 mg/l) with another commercially available particle-enhanced turbidimetric immunoassay. Cystatin C offers better clinical sensitivity than creatinine for discriminating patients with normal renal function and those with mild-to-moderate reduction in renal function. This method is suitable for routine cystatin C measurement, including emergencies.     

The effect of propionate on lipid synthesis in rat lymphocytes

1. The effect of propionate on lipid synthesis in lymphocytes cultured for 24 hr and incubated for 2 hr was investigated. 2. [1-14C]-propionate was incorporated mainly into phospholipids in both control and concanavalin A (Con A) stimulated cultured lymphocytes. 3. The content of free coenzyme A markedly decreased in 2 hr incubated lymphocytes when propionate was added to the medium at concentrations from 10 to 100 mmol/l. 4. Propionate at 40 mmol/l decreased the incorporation of [1-14C]-palmitate into phospholipids (86%), triacylglycerol (87%) and cholesterol ester (98%) and increased in cholesterol (133%) of cultured lymphocytes. 5. Addition of propionate into the culture medium at 2.5 and 5.0 mmol/l concentrations markedly increased the activity of hydrolases of various acylCoA derivatives. 6. The results suggest that propionate may reduce the content of acylCoA and so its esterification and this might be important for the regulation of lymphocytes proliferation.     

Evaluation of the new automated ELISA Vidas Lp(a) assay. Comparison with an immunonephelemetric method

Lipoprotein (a) [Lp(a)] is a lipoprotein which has a plasma concentration that is highly correlated with cardiovascular disease. In this study, the new Lp(a) assay for the Vitek Immuno-Diagnostic Assay System (VIDAS) developed by bioMérieux was evaluated. This method uses an enzyme linked fluorescent immunoassay (ELFIA) technique. Within-run and between-run reproducibility of the Vidass Lp(a) assay are characterized by coefficients of variation (CV) of 3 to 5.9% and 3.9 to 5.9%, respectively. Using analysis of variance, no statistical difference was shown between ELFIA and immunonephelometric assay (INA). When comparing results of the Vidas Lp(a) test with the INA, a highly significant correlation of r = 0.9708 and regression line equation y = 0.963x-0.037 was found. Interference of lipemia was studied: no influence was observed up to 12.3 mmol l(-1) triglycerides. No interference of haemoglobin was noted for Lp(a) > 0.20 g l(-1). Hyperbilirubinemia ( > 120 micromol l(-1)) led to results being underestimated for concentrations of Lp(a) which were < 0.20 g l(-1). No pre-analytical interference of citrate was measured but pre-analytical interference of EDTA was found. In conclusion, this new fully automated immunofluorimetric Lp(a) assay enables to the rapid, accurate and reliable determination of Lp(a) in blood samples.     

Validation and study of the transferability of the selected technique by SFBC for the determination of creatinine in plasma

A selected method for the determination of creatinine in plasma, using the reaction with alkaline picrate without prior pretreatment has been proposed by the Commission 'Validation de techniques' in the SFBC (Société Fran?aise de biologie clinique). The transferability step was conducted in seven laboratories, equipped with different automatic analyzers, using analytical procedures derived from the recommended method. Its goal was to test whether the original analytical performances could be maintained and consistent results obtained. The validation step was designed to evaluate the linearity limits of the analytical range, the detection limit, to assess accuracy as compared to a high performance liquid chromatography and to investigate the effect of the main interferents. Linearity limits are 15 and 2000 mumol/L. The detection limit is 3 to 8 mumol/L according to the analytical systems. The selected method can fulfil the set imprecision goals: intralaboratory CV minus than 2% (within-run), minus than 4% (run-to-run), interlaboratory CV minus than 5% (for 100 mumol/L creatinine). Inaccuracy evaluated for the chosen control sera is 1 to 15% as compared to the chromatographic method, according to the sera and to the analytical systems. The results obtained with the selected method are more consistent with the HPLC than are those obtained with an alkaline picrate method without SDS or with an enzymatic method. No interference could be demonstrated for acetoacetate (up to 8 mmol/L), hemoglobin (up to 210 mumol/L), unconjugated bilirubin (up to 250 mumol/L), glucose (up to 30 mmol/L), IgG (up to 45 g/L), albumin (up to 60 g/L). The effect of cephalosporins depends on the molecule. The reagents are stable for at least 6 months when stored in closed vials at +20 degrees C. The alkaline reagent is stable 30 days at +4 degrees C. Reference limits (0.025 and 0.975 fractiles) have been established for healthy adults. They are respectively 73 to 126 mumol/L for men and 59 to 100 mumol/L for females.     

Prenatal diagnosis of Smith-Lemli-Opitz syndrome is possible by measurement of 7-dehydrocholesterol in amniotic fluid

Amniocentesis was performed at 17.3 weeks in a pregnancy with severe intrauterine growth retardation. Cytogenetic studies on amniocytes were normal, 46,XX, and the pregnancy was continued. The diagnosis of Smith-Lemli-Opitz syndrome was suspected in the neonatal period and confirmed by the presence of 7-dehydrocholesterol (7-DHC) in the plasma (0.4 mmol/l, normal = not detectable) associated with a low total cholesterol concentration (0.4 mmol/l, normal = 2.56 +/- 0.23). Retrospective analysis of the amniotic fluid sample revealed an elevated level of 7-DHC (0.022 mmol/l; normal = undetectable). Therefore measurement of 7-DHC levels in amniotic fluid during the second trimester of pregnancy is useful for the prenatal diagnosis of Smith-Lemli-Opitz syndrome in families at risk and should be considered in cases of severe growth retardation of unknown aetiology for which amniotic fluid is available and in which a normal chromosomal pattern in amniocytes is present.     

Fluorides in the body of the mother and in the fetus. III. Fluorides in amniotic fluid

Fluoride concentrations in amniotic fluid as well as in venous and arterial cord blood serum were determined in 20 women during the perinatal period. The mean concentrations of fluoride from amniotic fluid, venous cord blood serum and arterial cord blood serum were 1,6 +/- 0,18 mumol/l, 3,2 +/- 0,28 mumol/l and 2,9 +/- 0,39 mumol/l respectively. Amniotic fluid fluoride concentrations were significantly higher in the older age group of pregnancies (39-42 weeks) in comparison with the younger age group of pregnancies (34-38 weeks) p < 0,01. The reasons for mentioned relations were discussed.     

Antibody interference in thyroid assays: a potential for clinical misinformation

Measurements of thyrotropin and of total and free thyroxine and triiodothyronine are widely used diagnostic methods for thyroid function evaluation. However, some serum samples will demonstrate a nonspecific binding with assay reagents that can interfere with the measurement of these hormones. Several recent case reports have described the presence of such interferences resulting in reported abnormal concentrations of thyroid hormones inconsistent with the patient's thyroid state. Circulating thyroid hormone autoantibodies, described in thyroid and nonthyroid disorders, are an important class of interference factor and can bind to hormone tracers used in various immunoassays. Two additional categories of interfering antibodies may particularly interfere within two-site immunoassays for thyrotropin. These include heterophile antibodies, especially human anti-mouse antibodies, and rheumatoid factors, which can cause interferences by immunoglobulin aggregation and (or) cross-linking of both capture and signal antibodies. Here we review the nature of these disturbances; their occurrence, prevalence, and detection; and the clinical consequences of the failure to recognize such interference.     

Time-resolved immunofluorometric assay for the quantification of lipoprotein(a) in serum

Although two recent studies have failed to reveal lipoprotein(a) (LP(a)) serum concentrations > 300 mg/l to be an independent risk factor for early onset of atherosclerosis, Lp(a) serum concentrations are frequently measured to evaluate the additional risk of coronary heart disease. We describe a time-resolved immunofluorometric assay (TRIFMA) for quantifying Lp(a) levels in humans serum using commercially available reagents, which is rapid, robust and simple to perform. The two-site immunometric assay was based on microtitre plates as solid phase coated with a polycloncal anti Lp(a) antibody. The liquid-phase antibody was labelled with biotin and detected by europium labelled streptavidin in the DELFIA 1232 fluorometer. The measuring range was 2-1600 mg/l. The intra-assay imprecision was < 7% (CV), the inter-assay imprecision < 12% (CV). No interference was detected with plasminogen concentration up to 2.2 g/l. There was an acceptable correlation with a commercially available enzyme immunoassay (r = 0.95) and with electroimmunodiffusion (r = 0.85) on 100 routine serum samples measured. The assay appeared to detect different Lp(a) isoforms as dilution curves were parallel for B/F, S2 and S4 isoforms.     

1H-nuclear magnetic resonance studies of human synovial fluid in arthritic disease states as an aid to confirming metabolic activity in the synovial cavity

1. A 1H-n.m.r. method was used to measure concentrations of valine, alanine, lactate, acetate, hyaluronan and lipids in synovial fluid obtained, during the normal course of examination from the knee joints of patients attending rheumatology and orthopaedic clinics. Fluid was available from 16 patients with osteoarthritis, 18 patients with rheumatoid arthritis, four patients with meniscal tear and one patient each with systemic lupus erythematosis, mono-arthritis, synovitis and loose bodies. Four normal specimens were obtained for comparison. 2. Valine, alanine and acetate levels all showed a normal Gaussian distribution, reflecting the distributions within the serum of the sample population. 3. Lactate concentrations divided into two distinct patterns. At concentrations below 2.5 mmol/l the lactate levels showed a Gaussian distribution, reflecting the distribution in normal serum. The normal synovial fluid specimens belong to this distribution. Above 2.5-3.0 mmol/l, lactate levels were asymmetric in distribution with a long tail at higher concentrations. These high levels of lactate can be explained by the generation of lactate through anaerobic metabolism within the synovial cavity. This metabolic process is triggered by a general inflammatory condition such as in rheumatoid arthritis. 4. The distribution of n.m.r.-observable lipid concentrations in rheumatoid arthritis and osteoarthritis each shows a normal distribution and the mean concentration is significantly higher in rheumatoid arthritis. 5. An increased n.m.r.-observable hyaluronan concentration is associated with an inflammatory situation. 6. It is concluded that raised levels of lactate and n.m.r.-observable hyaluronan and lipids are useful markers to aid the clinical distinction between rheumatoid arthritis and osteoarthritis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reference values of common blood chemistry analytes in healthy population of Rawalpindi-Islamabad area

The reference values of common blood chemistry analytes in healthy population, aged newborn to 80 years, of Rawalpindi Islamabad area were determined at AFIP, Rawalpindi. A total of 2115 healthy subjects, 1206 males and 909 females, were included in the study. Plasma glucose was analysed by GOD/POD, serum cholesterol by CHOD/PAP, triglycerides by GPO/PAP, urea by urease/GLDH, creatinine by Jaffe' rate reaction, uric acid by uricase, total bilirubin by Jendrassik and Grof, total protein by biuret, alanine transaminase (ALT) by optimized IFCC and alkaline phosphatase (AP) by optimized DGKC method. The between batch CVs of all the parameters were within acceptable quality goals. The reference values were calculated using 2.5 and 97.5 percentiles as lower and upper limits (95% CI). In healthy adult males the reference values were: fasting plasma glucose, 3.6-6.0 mmol/l; serum cholesterol; 3.2-6.6 mmol/l; triglycerides, 0.6-2.3 mmol/l; urea, 2.8-6.4 mmol/l; creatinine, 65-132 umol/l; uric acid, 164-430 umol/l; total bilirubin, 5-18 umol/l; total protein, 57-83 g/l; ALT, 15-45 U/l and AP, 185-620 U/l. The values in adult females, children and elderly subjects were slightly different than adult males. The reference values of our population show mild to moderate differences from the other Asian, European and American populations. It is recommended that reference values of different biochemical investigations should be established in various areas of Pakistan to make appropriate use of such investigations.     

Dexamethasone levels in treated pregnant women and newborn infants

Dexamethasone concentration was measured in plasma and amniotic fluid by radioimmunoassay using a rabbit antiserum raised against DX-hemisuccinate-albumin. Recoveries of added tracers averaged 70% after paper chromatography. The within- and between-assay coefficients of variation averaged 10%. The lower limit of detection was 0.2 mug/dl when 0.4 ml of plasma was assayed. Ten healthy pregnant women at term had cesarean sections 8 to 11 hours following administration of 8 mg of DX orally. DX levels in maternal vein, in umbilical vein and artery, and in amniotic fluid averaged 2.2, 2.9, 2.6, and 2.5 mug/dl, respectively. Although cortisol levels were markedly suppressed, the total relative glucocorticoid activity in blood of fetuses treated with DX far exceeded that of the untreated group.     

Multicentre evaluation of the EBIO plus glucose analyser

The EBIO plus, a newly developed dedicated glucose analyser, was tested at three different sites for its analytical characteristics and practicability. Results were linear over a range of 2-50 mmol/l, precision was satisfactory (overall CV < 5.3% at a concentration level of 1.8 mmol/l and < 3.7% at a concentration level of 4.5-21 mmol/l). Calibration was stable up to 90 minutes. No significant influences were observed for several potential interfering substances at physiological or therapeutical levels. Practicability was found to be good. Sample through-put depends on calibration frequency and is maximally 166 per hour. Some problems with outliers had to be overcome in the beginning of the evaluation period, but in the end all evaluators concluded that the EBIO plus is user friendly with good analytical characteristics.     

Cholecystectomy with intraperitoneal drain. Presence and significance of conjugated bilirubin in the drainage fluid

The content of conjugated bilirubin in the drainage fluid of 85 patients, operated upon consecutively with cholecystectomy and intraperitoneal drain for nonacute gallbladder pathology was measured by the adapted method of Jendrassik and Grof. The measured amounts varied from 0 to 755 micromol. A weak correlation was found between the concentration of conjugated bilirubin and the total amount of drainage fluid (r = 0.37). In the majority of patients the evacuated amounts of conjugated bilirubin corresponded to the content of bilirubin in a few milliliters of hepatic bile. In 10% of the patients there were however greater amounts of conjugated bilirubin in the drainage fluid. Greater amounts of conjugated bilirubin were significantly more often evacuated from patients operated upon by surgeons with less than 3 years of surgical experience compared to patients operated upon by more experienced surgeons. The amount of conjugated bilirubin in the drainage fluid was not significantly correlated with operative blood loss, dryness of the operative field at the end of the operation or iatrogenic perforation of the gallbladder during operation. Higher (however not significant) temperatures and bilirubin levels in serum were observed in patients with greater amounts of conjugated bilirubin in the drainage fluid. Increased amounts of conjugated bilirubin in the drainage fluid were not significantly associated with increased postoperative morbidity. Two of the patients with large amounts of conjugated bilirubin in the drainage fluid were reoperated because of bile leakage/abscess but the remaining patients had no serious complication, which could be a result of efficiency of the intraperitoneal drain.     

The effect of transport-blocking drugs on secretion of fluid and electrolytes by the mandibular gland of red kangaroos, Macropus rufus

Mechanisms of primary fluid formation by macropodine mandibular glands were investigated in anaesthetized red kangaroos using ion-transport and carbonic anhydrase inhibitors. Bumetanide at carotid plasma concentrations of 0.005-0.1 mmol/l progressively reduced a stable, acetylcholine-evoked flow rate of 1.02 +/- 0.024 ml/min to 0.16 +/- 0.016 ml/min (mean +/- SEM). Concurrently, saliva [Na], [Cl] and osmolality decreased, [K] and [HCO3] increased and HCO3 excretion was unaffected. High-rate cholinergic stimulation was unable to increase salivary flow above 12 +/- 1.5% of that for equivalent pre-bumetanide stimulation. Furosemide (1.0 mmol/l) and ethacrynate (0.5 mmol/l) caused depression of salivary flow and qualitatively similar effects on ion concentrations to those of bumetanide. Amiloride (up to 0.5 mmol/l) caused no reduction in salivary flow rates or [Na] but decreased [K] and [Cl] and increased [HCO3]. When compared with bumetanide alone, amiloride combined with bumetanide further augmented [K] and [HCO3] and lowered [Cl], but had no additional effects on Na or flow. At the higher level, 4-acetamido-4'- isothiocyanatostilbene-2,2'disulphonic acid (SITS) (0.05 and 0.5 mmol/l) stimulated fluid output, increased [HCO3] and [protein], and depressed [Na], [K] and [Cl]. Relative to bumetanide alone, SITS given with bumetanide had no additional effects on salivary flow or electrolytes. Methazolamide (0.5 mmol/l) in combination with bumetanide curtailed the decrease in [Cl] and the increases in [K] and [HCO3] associated with bumetanide. The residual methazolamide-resistant HCO3 excretion was sufficient to support 2-6% of primary fluid secretion. It was concluded that secretion of primary fluid by the kangaroo mandibular gland is initiated mainly (> 90%) by Cl transport resulting from Na-K-2Cl symport activity. A small proportion of the fluid secretion (up to 6%) appears to be supported by HCO3 secretion. No evidence was found for fluid secretion being dependent on Cl transport involving Na/H and Cl/HCO3 antiports or on HCO3 synthesis involving carbonic anhydrase.     

Haemoglobin O Padova and falsely low haemoglobin A1c in a patient with type I diabetes

Glycated haemoglobin (HbA1c) measured by high performance liquid chromatography (HPLC) in a 20 year old female with insulin dependent diabetes mellitus was consistently within the normal range although her daily blood glucose values were > 11.1 mmol/l. HbA1c measured by immunoagglutination and fructosamine was elevated and correlated with the patient's blood glucose values. The HPLC chromatogram showed an additional peak at HbA0. Electrophoresis of haemoglobin on citrate agar gel revealed an abnormal haemoglobin anodal of HbS. Cellulose acetate electrophoresis and isoelectric focusing demonstrated an additional haemoglobin migrating close to HbA2. Amino acid analysis and DNA sequencing revealed an alpha 30 (B11) Glu-->Lys replacement, that is, haemoglobin O Padova. Investigations of two family members without diabetes revealed the same rare haemoglobin variant. This case showed that this silent haemoglobin mutation caused an additional peak and falsely low HbA1c values when measured by HPLC, the gold standard for this evaluation.     

The determination of inorganic sulphate in serum and synovial fluid by high performance ion chromatography

A method for the determination of inorganic sulphate based on high performance ion chromatography is presented. The separation was performed on an anion-exchange column with a 1.8 mmol/l sodium carbonate/ 1.7 mmol/l sodium hydrogen carbonate-buffer, pH 10.35. Conductivity of the eluate was monitored after suppression of the background conductivity caused by the eluent-buffer. Serum and synovial fluid samples were prepared by ultrafiltration through membranes with a molecular mass cutoff of M(r) 10,000. The viscosity of the synovial fluids was reduced by treatment with hyaluronate lyase before ultrafiltration. The method showed a linear response for sulphate concentrations between 0.5 and 1000 mumol/l. The limit of detection was 1 mumol/l for aqueous standards. For serum the coefficient of variation within-run was 2.3%-2.4%, the coefficient of variation between days 2.9%-3.1%. For synovial fluids the coefficient of variation within-run was 3.1%-3.4%, the coefficient of variation between days 4.6%-5.7%. Standard recovery experiments performed by spiking pools of human sera containing low sulphate concentrations with sulphate concentrations between 5 mumol/l and 40 mumol/l showed recoveries between 98.9% and 100.6%. The corresponding experiments with pools of synovial fluids showed recoveries of 98.3% to 100.9%. As determined from 127 serum samples the reference range for sulphate was 262 mumol/l-420 mumol/l, with a mean value of 314 mumol/l. No dependence on age or sex was observed. The sulphate concentration in 36 synovial fluids from knees affected by inflammatory processes showed a mean value of 424 mumol/l and a standard deviation of 70 mumol/l. In 41 synovial fluids from knees affected by chronic degeneration joint disease, the sulphate concentrations were statistically significantly lower, with a mean of 374 mumol/l and a standard deviation of 58 mumol/l. The concentrations of sulphate in the synovial fluids were statistically significantly higher than those in the serum samples used for determination of the reference range. Following the oral application of a subtoxic single dose of acetaminophen (32.5 mg/kg body weight-62.5 mg/kg body weight) to 4 healthy volunteers, there was a significant decrease in the concentration of sulphate in serum with a minimum at 4-5 h after application of the drug. The cumulative concentration decrease of sulphate in serum and the kinetic constant of the sulphate depletion were not correlated with the applied acetaminophen dose normalized for body weight.     

An evaluation of the Ektachem serum lithium method and comparison with flame emission spectrometry

We evaluated the performance of a new colorimetric method in dry chemistry for serum lithium (Li) assay using an Ektachem E500 analyser. Imprecision results were acceptable and the linearity was verified for concentrations within the range of 0.2-3.9 mmol l-1, i.e. y(measured) = 1.02x(calculated) + 0.07, r = 0.99. The Ektachem Li assay was unaffected by potassium (K), calcium (Ca) and magnesium (Mg) at all concentrations tested. Significant interference was caused by sodium (Na) and haemoglobin. Statistically and clinically significant interference was caused by high concentrations of Na (213 mmol l-1) with a bias of 0.20 mmol l-1 (p = 0.02) and by high levels of haemoglobin (280 mumol l-1) with a bias of 0.20 mmol l-1 (p = 0.01). Comparison of serum Li results from 80 patient samples assayed using the Ektachem method with those obtained using the IL943, a flame atomic emission spectrometry (FAES)-based method, gave a regression line equation: Ektachem = 0.95xFAES + 0.13, r = 0.96. The data revealed a mean difference of 0.10 mmol l-1 between the Ektachem and FAES results that was statistically significant (p = 0.01), but clinically negligible. We conclude that the Kodak method provides reliable Li serum results and represents a valid alternative to the FAES method.     

Carnitine determination by an enzymatic cycling method with carnitine dehydrogenase

We describe a highly sensitive and specific method for determining L-carnitine in serum by use of carnitine dehydrogenase (EC 1.1.1.108). The method involves a new enzymatic cycling technique with NADH, thio-NAD+, and carnitine dehydrogenase, and measures the increase of absorbance at 415 nm of thio-NADH produced at 37 degrees C during the reaction: [formula: see text] The calibration curve for L-carnitine in serum was linear between 5 and 250 mumol/L. Analytical recovery was 96.5-106%, and within-run and between-run imprecisions (CV) were 0.66-4.33% and 1.02-2.56%, respectively. This method was free from interference by bilirubin, hemoglobin, various acyl-DL-carnitines, and ascorbate. The procedure is simple, rapid, accurate, and automatable. The amount of free L-carnitine in serum (53.6 +/- 11.7 mumol/L, n = 200) was greater in men than in women (45.1 +/- 14.2 mumol/L, n = 200) (mean +/- SD).