Polycyclic aromatic hydrocarbons in residential dust and risk of childhood acute lymphoblastic leukemia.

Several polycyclic aromatic hydrocarbons (PAHs) are known or probable human carcinogens. We evaluated the relationship between PAH exposure and risk of childhood acute lymphoblastic leukemia (ALL) using concentrations in residential dust as an exposure indicator. We conducted a population-based case-control study (251 ALL cases, 306 birth-certificate controls) in Northern and Central California from 2001 to 2007. We collected residential dust using a high volume small surface sampler (HVS3) (n=185 cases, 212 controls) or by sampling from participants' household vacuum cleaners (n=66 cases, 94 controls). We evaluated log-transformed concentrations of 9 individual PAHs, the summed PAHs, and the summed PAHs weighted by their carcinogenic potency (the toxic equivalence). We calculated odds ratios (ORs) and 95% confidence intervals (CI) using logistic regression adjusting for demographic characteristics and duration between diagnosis/reference date and dust collection. Among participants with HVS3 dust, risk of ALL was not associated with increasing concentration of any PAHs based on OR perln(ng/g). Among participants with vacuum dust, we observed positive associations between ALL risk and increasing concentrations of benzo[a]pyrene (OR perln[ng/g]=1.42, 95% CI=0.95, 2.12), dibenzo[a,h]anthracene (OR=1.98, 95% CI=1.11, 3.55), benzo[k]fluoranthene (OR=1.71, 95% CI=0.91, 3.22), indeno[1,2,3-cd]pyrene (OR=1.81, 95% CI=1.04, 3.16), and the toxic equivalence (OR=2.35, 95% CI=1.18, 4.69). The increased ALL risk among participants with vacuum dust suggests that PAH exposure may increase the risk of childhood ALL; however, reasons for the different results based on HVS3 dust samples deserve further study.

A rapid luminescently monitored enzyme immunoassay for IgE.

A novel halophenol-enhanced luminol-peroxide luminescent detection method for horseradish peroxidase has been tested in an enzyme immunoassay for IgE. The luminescent enzyme immunoassay was reproducible (within-batch CV, 3.9-13.2%) and values obtained on serum samples showed good agreement with those obtained by colorimetric enzyme immunoassay. The major advantages of the luminescent detection method are that it is rapid, 30 s compared with 30 min for the colorimetric assay using o-phenylenediamine, and the luminescent signal is intense and stable for several minutes.

Adsorption of serum calcium by plastic sample cups.

Sera left overnight in plastic AutoAnalyzer sample cups may give low calcium values; the effect is attributed to adsorption of calcium onto the walls of the vessel. The adsorption is brought about by a rise in the pH of the sera, and factors which promote the rise in pH increase the adsorption. This phenomenon is of practical importance because as much as 10% of the calcium in the serum may be adsorbed. Adsorption occurs particularly onto the walls of polystyrene cups, and when polypropylene cups were used the adsorption was reduced. The phenomenon cannot be evaluated or controlled by the use of control sera. In order to avoid the sampling error, serum for calcium analysis should be used fresh or stored at 4 degrees C under conditions such that any change in pH is minimal. Sera should not be left to stand in AutoAnalyzer cups at room temperature for longer than three hours before analysis.

External quality assessment of clinical laboratories in the United Kingdom.

A review is given of the National External Quality Assessment Schemes (NEQASs) in various pathology disciplines in the United Kingdom, with a discussion of the relative roles of the DHSS, individual laboratory scientists, and the relevant professional bodies. Principles of operation and scientific problems in the design of NEQASs in different disciplines are described and contrasted, and some comparisons with the experience in other European countries and the USA are drawn.

A comparative survey of the results of analyses of blood serum in clinical chemistry laboratories in the United Kingdom.

Since July 1969, portions of the same blood serum have been dispatched to clinical chemistry laboratories in the United Kingdom at 14-day intervals. The results of each serum survey were reported to each of the 390 participants within 11 days of their originally receiving the specimen. During the first 18 months of the survey no overall improvement in the results was seen. Therefore a summary of each laboratory's ability consistently to produce results close to the mean of the method used was calculated and reported as a single figure, the variance index, and sent to all participants at regular intervals together with a histogram distribution of the variance indices of other participants. The subsequent improvement in the overall results is described.

Enhanced luminescence enzyme immunoassay for factor VIII related antigen.

A sandwich enzyme immunoassay for plasma factor VIII related antigen has been developed which exploits a para-iodophenol enhanced chemiluminescent reaction to detect the horseradish peroxidase label. The assay entailed 15 min incubations with sample and with conjugate and had a detection limit of 0.12 mU. It showed good within batch precision (coefficient of variation = 2.95-5.8%) and results on a series of 57 specimens agreed with results obtained by immunoelectrophoresis (correlation coefficient = 0.97).

A rapid chemiluminescent enzyme-linked immunosorbent assay for cytomegalovirus immunoglobulin G antibodies using instant photographic film.

A rapid and convenient chemiluminescent enzyme-linked immunosorbent assay (ELISA) for IgG antibodies to cytomegalovirus has been developed which uses low cost equipment. Assays were carried out on transparent microtitre plates and used an anti-human IgG horseradish peroxidase conjugate. Bound peroxidase was detected chemiluminescently using a p-iodophenol-luminol-peroxide reagent. Light emission from the wells of the microtitre plate was detected on instant photographic film (ASA 20,000) held in a specially designed shutter type camera. The semi-quantitative technique was tested in a routine laboratory for a period of 7 wk and the results obtained compared well (95.3% agreement) with those obtained by a conventional colorimetric ELISA using an alkaline phosphatase label.

Risk factors for ischaemic heart disease: the prospective phase of the British Regional Heart Study.

Risk factors for major ischaemic heart disease (acute myocardial infarction or sudden death) have been investigated in a prospective study of 7735 men aged 40-59 years drawn from general practices in 24 British towns. After a mean follow-up of 4.2 years, there have been 202 cases of major ischaemic heart disease. Univariate estimates of the risk of ischaemic heart disease show that serum total cholesterol, HDL-cholesterol and triglyceride concentrations, systolic and diastolic blood pressures, cigarette smoking, and body mass index are all associated with increased risk of ischaemic heart disease. Evidence of ischaemic heart disease at initial examination is also strongly associated with increased risk of subsequent ischaemic heart disease. All these factors were then considered simultaneously using multiple logistic models. Definite myocardial infarction on electrocardiogram and recall of a doctor diagnosis of ischaemic heart disease remained predictive of subsequent major ischaemic heart disease, after allowance for all other risk factors. Serum total cholesterol, blood pressure, and cigarette smoking each remained as highly significant independent risk factors whereas overweight, above average levels of HDL-cholesterol and serum triglyceride were not predictive of risk after allowance for the above factors. Men with and without pre-existing ischaemic heart disease were examined separately in the same way (using multiple logistic models). The strength of association between the principal risk factors and subsequent major ischaemic heart disease was reduced in the men with pre-existing ischaemic heart disease, only age and serum total cholesterol remaining highly significant. Overall the levels of the major risk factors commonly encountered in British men have a marked effect on the risk of ischaemic heart disease. Modification of these risk factors in the general population constitutes an important national priority.

Matrix effects in clinical analysis: commutability of control materials between the Ektachem, Beckman and SMA 12/60 glucose and urea methods.

The effects of the protein matrices of selected human and animal based control materials on the Ektachem, Beckman and SMA 12/60 glucose and urea methods have been investigated by means of commutability studies. The commutability of control materials between the Ektachem and SMA 12/60 was greater than that between the Ektachem and Beckman methods and was similar to that reported for conventional methods. No trends were apparent amongst control sera from different species nor with different total protein levels. Some variation in commutability was found with different batches of Ektachem glucose and urea slides. In addition the effect of lyophilisation of fresh human serum on its analytical behaviour with different experimental batches of Ektachem glucose/urea slides was studied and found to be negligible.

Characterisation of the protein matrix of quality control sera by a high resolution two-dimensional electrophoresis technique.

A high resolution two-dimensional electrophoresis technique (Iso-Dalt) has been employed to characterise the protein components of freshly drawn human serum and various human- and animal-based quality control sera. This technique allows a direct comparison to be made between the protein components of different materials. Similarities have been demonstrated between the protein components (protein matrix) of freshly drawn human serum and human-, equine- and bovine-based control sera, though some differences existed between sera from these three sources, mainly in the acidic high molecular weight quadrant and the lipoprotein and haptoglobin regions. The Iso-Dalt technique also revealed differences in the protein matrices of the various human-based quality control sera tested. Differences attributable to manufacturing technique were also discernible by inspection of the two-dimensional maps of the protein matrices. Although characterisation and comparison of protein components of the matrix of serum is difficult, the Iso-Dalt technique has proved a valuable tool in this characterisation and the subsequent assessment of the similarity of quality control sera to human serum. This type of information is valuable when considering the suitability of human- or animal-based sera for use in internal and external quality control procedures.

Outlying values in the National Quality Control Scheme.

A modified statistical method for the detection of outlying values has been applied to five fortnightly sets of data from the National Quality Control Scheme. The overall outlier rate was 2.4%, not varying greatly between analytes. Many of the outliers appear to be due to sample identification errors.

Effect of body mass and other factors on serum liver enzyme levels in men attending for well population screening.

Alcohol abuse is usually regarded as the most likely cause of elevated serum liver enzyme values in those attending for well population screening, but we have found increased body weight to be an important contributing factor. We have measured serum levels of alanine amino-transferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT) in approximately 21,000 men attending for routine health screening, and related these to behavioural factors such as alcohol consumption, cigarette smoking, exercise level and obesity. The levels of all three enzymes were positively correlated with levels of alcohol consumption. Decreasing levels of physical activity were associated with increases in mean ALT and GGT levels. Cigarette smoking showed only a weak effect on ALT and AST, which became non-significant after multivariate statistical analysis, but increasing consumption of cigarettes was associated with increased mean levels of GGT. In contrast, all three enzymes showed marked increases in mean levels with increasing body mass index (BMI). The effect of obesity was particularly important in the case of ALT: the prevalence of increased ALT values in obese subjects (BMI greater than or equal to 31 kg/m2) was more than eight times that in those with normal weight (BMI less than or equal to 25 kg/m2), even after allowing for the confounding effect of alcohol consumption. This study is concerned solely with male subjects, but we hope to extend the analysis to females in the near future.

An examination of the hexokinase method for serum glucose assay using external quality assessment data.

Hexokinase methods for serum glucose assay appeared to give slightly but consistently higher inter-laboratory coefficients of variation than all methods combined in the UK External Quality Assessment Scheme; their performance over a two-year period was therefore compared with that for three groups of glucose oxidase methods. This assessment showed no intrinsic inferiority in the hexokinase method. The greater variation may be due to the more heterogeneous group of instruments, particularly discrete analysers, on which the method is used. The Beckman Glucose Analyzer and Astra group (using a glucose oxidase method) showed the least inter-laboratory variability but also the lowest mean value. No comment is offered on the absolute accuracy of any of the methods.

The effects of cigarette smoking and alcohol consumption on serum liver enzyme activities: a dose-related study in men.

The separate and joint effects of cigarette smoking and alcohol consumption on serum activities of the enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyl transferase (GGT) were investigated in 46,775 men attending the BUPA Health Screening Centre in London during the period 1983-1987, after allowing for differences in age, body mass index and exercise level. As expected, all showed a significant positive correlation with alcohol consumption. Cigarette smoking produced a significant increase in GGT activity in all drinking categories bar teetotallers, particularly for those smoking more than 20 cigarettes per day. There were no changes of clinical significance in AST or ALT activities with smoking. We postulate that the combined effects of alcohol and smoking on GGT activity are a result of induction of the enzyme by both alcohol and nicotine. Smoking as well as drinking habits should be taken into account when assessing the significance of an individual's enzyme activities.

The effects of cigarette smoking and alcohol consumption on blood lipids: a dose-related study on men.

The separate and joint effects of cigarette smoking and alcohol consumption on serum concentrations of total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides were investigated in 46 750 men attending the BUPA Health Screening Centre in London during the period 1983-1987, after allowing for differences in age, body mass index and exercise level. Drinking alcohol was found to raise both total cholesterol and HDL-C concentrations, in such a way that HDL-C as a percentage of total cholesterol increased with increasing alcohol consumption. LDL-C concentrations increased with increasing alcohol consumption in non-smokers, but decreased in those smoking over 10 cigarettes per day. Drinking had no significant effect on triglycerides except at high levels of consumption. Smoking raised total cholesterol, LDL-C and triglycerides, but lowered HDL-C concentrations. In particular, smoking even small amounts could negate any protective benefit in HDL-C concentrations gained from moderate consumption of alcohol. Assuming a desirable lipid profile to consist of low total cholesterol, LDL-C and triglycerides and a high HDL-C value, this is best achieved for men by being a non-smoking moderate drinker.

Evaluation of the Kodak Ektachem glucose and urea methods.

An evaluation of the Kodak Ektachem glucose and urea methods is described. Aspects evaluated included precision, linearity, accuracy, correlation with routine methods, interferences (haemoglobin, bilirubin, protein, dextran, lipaemia, ethylene-diamine tetraacetic acid, fluoride/oxalate, and heparin), and carryover. Stability and batch-to-batch variation in glucose and urea reagents were also investigated. The performance of the Ektachem glucose and urea methods was shown to be as satisfactory as conventional analytical methods. The requirement to reconstitute control serum samples in a bicarbonate diluent in order to obtain accurate results presents problems for the analysis of lyophilised specimens circulated by external quality assessment schemes. The complex calibration model and the significance of variation in the calibration parameters need further explanation. The Ektachem methods are designed specifically for use with human serum. However, the methods performed satisfactorily with cerebrospinal fluid, pleural effusions, and animal serum but not with urine.

Alkaline phosphatase activity in lyophilised quality control serum.

The rise in alkaline phosphatase activity has been studied after reconstitution of 16 commercial preparations of lyophilised quality control material. The effects of storage temperature and analytical method on the rise in activity have also been studied, with a view to producing a reconstitution protocol suitable for recommendation to participants in external quality control surveys. Great differences were found in the magnitude of this rise in activity; these differences can be reduced to negligible levels if the material is mixed for 30 minutes at ambient temperature after reconstitution and then stored for not more than 4 hours at 4 degrees C before assay.

External quality assessment of serum enzyme activity assays and the effect of calibration on interlaboratory concordance.

The design and results of a UK external quality assessment scheme for six enzymes are described, from 21 surveys over a period of 7 years. Improvements in interlaboratory agreement and the adoption of reliable methods are documented. The potential of enzyme calibration materials in further improving numerical concordance between laboratories using different assay conditions, including temperature, is demonstrated and discussed.

A direct assay for pyridoxal 5'-phosphate using pig heart apo-aspartate transaminase.

The development of a simple enzymatic method for the determination of blood and plasma pyridoxal 5'-phosphate (PLP) using pig heart apo-aspartate transaminase (apo-AST) is described. The technique requires three steps: sample extraction using perchloric acid, a binding step in which PLP in the sample extract is attached to the apo-AST and the enzymatic assay of the reconstituted holo-AST. PLP extracts were analysed with and without a known concentration of added PLP to correct for variation in recovery between different specimens. Procedures are outlined for manual and automatic analysis of the PLP extracts. Using the KONE Clinical Analyser after the extraction step, it is possible to measure enzyme activity in 100 specimens (i.e. 400 tubes) in a 5 h period. Results are shown from 185 healthy women aged 20-45 years, in which plasma PLP concentrations ranged from 5 to 165 nmol/L, and 142 men and 56 women in government service aged 17-64 years, whose plasma PLP ranged from 8 to 169 nmol/L. Values less than 20 nmol/L are believed to indicate vitamin B6 deficiency and the method is able to measure 5 nmol/L.

An interlaboratory survey of hydrogen ion and blood gas determinations.

A survey of [H+], Pco2, and Po2 analyses in 360 laboratories was conducted using three commercial control materials: two aqueous gas-equilibrated buffer solutions (General Diagnostics and IL) and one whole blood material (DADE). There was little difference in precision or accuracy between instruments, classified according to manufacturer into four groups, and materials for [H+] and Pco2, or in precision for Po2. There were, however, differences in accuracy between instrument groups for Po2 analysis on the aqueous materials, and in some cases the mean values lay outside the range assigned by the material manufacturers. The 35 instruments outside clinical chemistry departments yielded results similar to those of all participants. The relation between inter- and intra-laboratory precision was similar to that for many analytes, suggesting that neither these materials nor the state of these analyses is unsatisfactory. Aqueous materials should, however, be used with caution as accuracy controls for Po2.