Acute stroke CDS: automatic retrieval of thrombolysis contraindications from unstructured clinical letters

Introduction

Thrombolysis treatment for acute ischaemic stroke can lead to better outcomes if administered early enough. However, contraindications exist which put the patient at greater risk of a bleed (e.g. recent major surgery, anticoagulant medication). Therefore, clinicians must check a patient's past medical history before proceeding with treatment. In this work we present a machine learning approach for accurate automatic detection of this information in unstructured text documents such as discharge letters or referral letters, to support the clinician in making a decision about whether to administer thrombolysis.

Methods

We consulted local and national guidelines for thrombolysis eligibility, identifying 86 entities which are relevant to the thrombolysis decision. A total of 8,067 documents from 2,912 patients were manually annotated with these entities by medical students and clinicians. Using this data, we trained and validated several transformer-based named entity recognition (NER) models, focusing on transformer models which have been pre-trained on a biomedical corpus as these have shown most promise in the biomedical NER literature.

Results

Our best model was a PubMedBERT-based approach, which obtained a lenient micro/macro F1 score of 0.829/0.723. Ensembling 5 variants of this model gave a significant boost to precision, obtaining micro/macro F1 of 0.846/0.734 which approaches the human annotator performance of 0.847/0.839. We further propose numeric definitions for the concepts of name regularity (similarity of all spans which refer to an entity) and context regularity (similarity of all context surrounding mentions of an entity), using these to analyse the types of errors made by the system and finding that the name regularity of an entity is a stronger predictor of model performance than raw training set frequency.

Discussion

Overall, this work shows the potential of machine learning to provide clinical decision support (CDS) for the time-critical decision of thrombolysis administration in ischaemic stroke by quickly surfacing relevant information, leading to prompt treatment and hence to better patient outcomes.

A214 WOMEN WITH INFLAMMATORY BOWEL DISEASE HAVE INCREASED HEALTH-CARE UTILIZATION DURING PREGNANCY AND POSTPARTUM COMPARED TO THOSE WITHOUT INFLAMMATORY BOWEL DISEASE: A POPULATION-BASED COHORT STUDY

Background

Compared to those without inflammatory bowel disease (IBD), women with IBD may have increased health-care utilization during pregnancy and postpartum. This may lead to significant morbidity and decrease in quality of life. Characterizing this health-care use is important for health-policy purposes to determine methods to shift care to the ambulatory setting.

Purpose

We aimed to compare health-care utilization of women with and without IBD during preconception, pregnancy and postpartum.

Method

We accessed administrative databases and validated algorithms at the Institute of Clinical Evaluative Services (ICES) in Ontario to identify women (age 18-55) with and without IBD who had a completed live, singleton pregnancy between 2003 and 2018. The primary outcome was to characterize differences in emergency department (ED) visits and hospitalizations between women with and without IBD during the 12 months preconception, pregnancy, and in the 12 months postpartum. The secondary outcome was to assess differences in prenatal care between women with and without IBD. Multivariable negative binomial regression with generalizing estimating equations, accounting for multiple pregnancies for each patient, was performed to report incidence rate ratios (IRR) with 95% confidence intervals (95% CI). Covariates included maternal age at conception, location of residence at conception (rural vs. urban), socioeconomic status (using surrogate marker of neighborhood income quintile), and maternal comorbidity.

Result(s)

9158 pregnancies in 6163 women with IBD and 1,729,411 pregnancies in 1,091,013 women without IBD were included. Women with IBD were older at time of delivery and had greater pre-pregnancy comorbidities. During pregnancy, women with IBD were more likely to visit the ED (IRR 1.13, 95% CI,1.08-1.18) and be hospitalized (IRR 1.11, 95% CI,1.01-1.21) for non-IBD specific reasons. Similarly, during postpartum, women with IBD were more likely to visit the ED (IRR 1.21, 95% CI, 1.15-1.27) and be hospitalized (IRR 1.18, 95% CI, 1.05-1.32) for non-IBD specific reasons. Venous thromboembolic events accounted for 7.0% of all postpartum hospitalizations in women with IBD compared to 2.7% in those without IBD (p<0.0001). There was no difference in ED visits and hospitalizations between women with and without IBD in preconception. Finally, women with IBD had greater number of prenatal visits with obstetricians during pregnancy and were more likely to receive a first trimester prenatal visit compared to those without IBD.

Conclusion(s)

Compared to those without IBD, women with IBD are more likely to visit the ED and be hospitalized during pregnancy and postpartum, particularly for venous thromboembolic events. Efforts should be made from a health policy perspective to increase access to ambulatory care for patients with IBD during the peripartum period which in turn may reduce acute setting health-services utilization.

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Disclosure of Interest

None Declared

Measuring contact angle and meniscus shape with a reflected laser beam

Side-view imaging of the contact angle between an extended planar solid surface and a liquid is problematic. Even when aligning the view perfectly parallel to the contact line, focusing one point of the contact line is not possible. We describe a new measurement technique for determining contact angles with the reflection of a widened laser sheet on a moving contact line. We verified this new technique measuring the contact angle on a cylinder, rotating partially immersed in a liquid. A laser sheet is inclined under an angle φ to the unperturbed liquid surface and is reflected off the meniscus. Collected on a screen, the reflection image contains information to determine the contact angle. When dividing the laser sheet into an array of laser rays by placing a mesh into the beam path, the shape of the meniscus can be reconstructed from the reflection image. We verified the method by measuring the receding contact angle versus speed for aqueous cetyltrimethyl ammonium bromide solutions on a smooth hydrophobized as well as on a rough polystyrene surface.

SysBioMed report: advancing systems biology for medical applications

The following report selects and summarises some of the conclusions and recommendations generated throughout a series of workshops and discussions that have lead to the publication of the Science Policy Briefing (SPB) Nr. 35, published by the European Science Foundation. (Large parts of the present text are directly based on the ESF SPB. Detailed recommendations with regard to specific application areas are not given here but can be found in the SPB. Issues related to mathematical modelling, including training and the need for an infrastructure supporting modelling are discussed in greater detail in the present text.)The numerous reports and publications about the advances within the rapidly growing field of systems biology have led to a plethora of alternative definitions for key concepts. Here, with 'mathematical modelling' the authors refer to the modelling and simulation of subcellular, cellular and macro-scale phenomena, using primarily methods from dynamical systems theory. The aim of such models is encoding and testing hypotheses about mechanisms underlying the functioning of cells. Typical examples are models for molecular networks, where the behaviour of cells is expressed in terms of quantitative changes in the levels of transcripts and gene products. Bioinformatics provides essential complementary tools, including procedures for pattern recognition, machine learning, statistical modelling (testing for differences, searching for associations and correlations) and secondary data extracted from databases.Dynamical systems theory is the natural language to investigate complex biological systems demonstrating nonlinear spatio-temporal behaviour. However, the generation of experimental data suitable to parameterise, calibrate and validate such models is often time consuming and expensive or not even possible with the technology available today. In our report, we use the term 'computational model' when mathematical models are complemented with information generated from bioinformatics resources. Hence, 'the model' is, in reality, an integrated collection of data and models from various (possibly heterogeneous) sources. The present report focuses on a selection of topics, which were identified as appropriate case studies for medical systems biology, and adopts a particular perspective which the authors consider important. We strongly believe that mathematical modelling represents a natural language with which to integrate data at various levels and, in doing so, to provide insight into complex diseases: 1. Modelling necessitates the statement of explicit hypotheses, a process which often enhances comprehension of the biological system and can uncover critical points where understanding is lacking. 2. Simulations can reveal hidden patterns and/or counter-intuitive mechanisms in complex systems. 3. Theoretical thinking and mathematical modelling constitute powerful tools to integrate and make sense of the biological and clinical information being generated and, more importantly, to generate new hypotheses that can then be tested in the laboratory.Medical Systems Biology projects carried out recently across Europe have revealed a need for action: 4. While the need for mathematical modelling and interdisciplinary collaborations is becoming widely recognised in the biological sciences, with substantial implications for the training and research funding mechanisms within this area, the medical sciences have yet to follow this lead. 5. To achieve major breakthroughs in Medical Systems Biology, existing academic funding schemes for large-scale projects need to be reconsidered. 6. The hesitant stance of the pharmaceutical industry towards major investment in systems biology research has to be addressed. 7. Leading medical journals should be encouraged to promote mathematical modelling.

Validity of autism diagnoses using administrative health data

It is necessary to monitor autism prevalence in order to plan education support and health services for affected children. This study was conducted to assess the accuracy of administrative health databases for autism diagnoses. Three administrative health databases from the province of Nova Scotia were used to identify diagnoses of autism spectrum disorders (ASD): the Hospital Discharge Abstract Database, the Medical Services Insurance Physician Billings Database and the Mental Health Outpatient Information System database. Seven algorithms were derived from combinations of requirements for single or multiple ASD claims from one or more of the three administrative databases. Diagnoses made by the Autism Team of the IWK Health Centre, using state-of-the-art autism diagnostic schedules, were compared with each algorithm, and the sensitivity, specificity and C-statistic (i.e. a measure of the discrimination ability of the model) were calculated. The algorithm with the best test characteristics was based on one ASD code in any of the three databases (sensitivity=69.3%). Sensitivity based on an ASD code in either the hospital or the physician billing databases was 62.5%. Administrative health databases are potentially a cost efficient source for conducting autism surveillance, especially when compared to methods involving the collection of new data. However, additional data sources are needed to improve the sensitivity and accuracy of identifying autism in Canada.

Validity of autism diagnoses using administrative health data

It is necessary to monitor autism prevalence in order to plan education support and health services for affected children. This study was conducted to assess the accuracy of administrative health databases for autism diagnoses. Three administrative health databases from the province of Nova Scotia were used to identify diagnoses of autism spectrum disorders (ASD): the Hospital Discharge Abstract Database, the Medical Services Insurance Physician Billings Database and the Mental Health Outpatient Information System database. Seven algorithms were derived from combinations of requirements for single or multiple ASD claims from one or more of the three administrative databases. Diagnoses made by the Autism Team of the IWK Health Centre, using state-of-the-art autism diagnostic schedules, were compared with each algorithm, and the sensitivity, specificity and C-statistic (i.e. a measure of the discrimination ability of the model) were calculated. The algorithm with the best test characteristics was based on one ASD code in any of the three databases (sensitivity=69.3%). Sensitivity based on an ASD code in either the hospital or the physician billing databases was 62.5%. Administrative health databases are potentially a cost efficient source for conducting autism surveillance, especially when compared to methods involving the collection of new data. However, additional data sources are needed to improve the sensitivity and accuracy of identifying autism in Canada.

Haloacetic acids in drinking water and risk for stillbirth

BACKGROUND

Trihalomethanes (THMs) occurring in public drinking water sources have been investigated in several epidemiological studies of fetal death and results support a modest association. Other classes of disinfection by-products found in drinking water have not been investigated.

AIMS

To investigate the effects of haloacetic acid (HAA) compounds in drinking water on stillbirth risk.

METHODS

A population based case-control study was conducted in Nova Scotia and Eastern Ontario, Canada. Estimates of daily exposure to total and specific HAAs were based on household water samples and questionnaire information on water consumption at home and work.

RESULTS

The analysis included 112 stillbirth cases and 398 live birth controls. In analysis without adjustment for total THM exposure, a relative risk greater than 2 was observed for an intermediate exposure category for total HAA and dichloroacetic acid measures. After adjustment for total THM exposure, the risk estimates for intermediate exposure categories were diminished, the relative risk associated with the highest category was in the direction of a protective effect, and all confidence intervals included the null value.

CONCLUSIONS

No association was observed between HAA exposures and stillbirth risk after controlling for THM exposures.

Analgesia for circumcision in a paediatric population: comparison of caudal bupivacaine alone with bupivacaine plus two doses of clonidine

BACKGROUND

Clonidine is often used to improve the duration and quality of analgesia produced by caudal epidural blockade, although the optimum dose of clonidine with bupivacaine remains uncertain.

METHODS

We compared the effect of clonidine, 1 and 2 microg x kg(-1), added to bupivacaine (1.25 mg x kg(-1)) with that of bupivacaine alone in 75 male children undergoing elective circumcision.

RESULTS

There was a trend towards increasing duration of analgesia with increasing dose of clonidine [group B (bupivacaine) 280.7 (171.6) min, C1 (bupivacaine + clonidine 1 microg x kg(-1)) 327.8 (188.3) min and C2 (bupivacaine + clonidine 2 microg x kg(-1)) 382.0 (200.6) min], although this difference was not statistically significant. Mean time to arousal from anaesthesia was significantly prolonged with clonidine 2 microg kg(-1) (group C2 21.3 (13-36) min, group C1 14.0 (6-25) min and group B 14.4 (2-32) min. Supplementary analgesic requirements and incidence of adverse effects were low, with no differences between the groups.

CONCLUSIONS

For paediatric circumcision, under general anaesthesia, the addition of clonidine 2 microg x kg(-1) to low volume (0.5 ml x kg(-1)) caudal anaesthetics has a limited clinical benefit for children undergoing circumcision.

Impact and inequity of inpatient waiting times for advanced cardiovascular services in community hospitals across the greater Toronto area

OBJECTIVE

To assess waiting times for inpatients requiring urgent transfer for advanced cardiovascular procedures from community hospitals; the magnitude of adverse events while waiting; and possible inequity among community hospitals in access to these services.

SETTING

Seven representative community hospitals in the Greater Toronto Area (GTA).

DESIGN

Prospective data collection over 12 months (May 1997 to April 1998).

PATIENTS

One thousand, two hundred and three inpatients who waited a total of 7261 hospital days for advanced cardiovascular procedures.

MAIN RESULTS

The average (+/- SD) inpatient waiting time, in days, for catheterization was 5.7+/-1.3, angioplasty 5.8+/-2.1, bypass surgery 7.0+/-2.1 and pacemakers 4.2+/-1.6. During this time there were 14 deaths (1.2%) and 12 (1.0%) morbid events in-hospital. Extrapolation of these data to all 21 community hospitals in the GTA suggests that annually 21,783 bed days are used by inpatients awaiting transfer for advanced cardiovascular procedures, during which time 42 fatal and 36 morbid events can be expected to occur. Of the seven hospitals, one had a catheterization laboratory (group 1), two had no laboratory but had catheterizing cardiologists (group 2), and four had no laboratory and no catheterizing cardiologists (group 3). None of these hospitals had on-site revascularization facilities. The average number of days spent waiting for catheterization in group 1 (3.1+/-0.4) was significantly less than that in group 2 (5. 4+/-1.3, P<0.001) and group 3 (6.5+/-1.3, P<0.0001). The catheterization wait in group 2 was significantly less than that in group 3 (P<0.02). There were no significant differences among the three groups in the number of days spent waiting for angioplasty or bypass surgery.

CONCLUSION

Waiting times for inpatients requiring advanced cardiovascular procedures in GTA community hospitals are long, and are associated with substantial morbidity and mortality. These waiting times also promote inefficient bed use and increased health care costs. Furthermore, these data suggest that access to inpatient coronary angiography in the GTA is inequitable and appears to depend more on the presence of on-site catheterization laboratories or catheterizing cardiologists than on illness severity.

Hospital marketing and the Internet: revisited

In 1995 a study was conducted to explore the use of the Internet in hospital marketing. Use of the Internet has exploded since that study was published. This manuscript replicates the 1995 study and extends it by investigating several managerial and operational issues concerning the use of the Internet in hospital marketing.

Customer centered health care: why managed care organizations must capitalize on new technology to build brands and customer loyalty

Now, more than ever, health care organizations are desperately trying to reach out to customers and establish stronger relationships that will generate increased loyalty and repeat business. As technology, like the Internet and related mediums, allow us to do a better job of managing information and communication, health care executives must invest the time and resources necessary to bring these new advances into the day-to-day operations of their businesses. Those that do will have a head start in building their brand and their customer loyalty.

Charge density study with the Maximum Entropy Method on model data of silicon. A search for non-nuclear attractors

In 1990 Sakata and Sato applied the maximum entropy method (MEM) to a set of structure factors measured earlier by Saka and Kato with the Pendellösung method. They found the presence of non-nuclear attractors, i.e., maxima in the density between two bonded atoms. We applied the MEM to a limited set of Fourier data calculated from a known electron density distribution (EDD) of silicon. The EDD of silicon was calculated with the program ADF-BAND. This program performs electronic structure calculations, including periodicity, based on the density functional theory of Hohenberg and Kohn. No non-nuclear attractor between two bonded silicon atoms was observed in this density. Structure factors were calculated from this density and the same set of structure factors that was measured by Saka and Kato was used in the MEM analysis. The EDD obtained with the MEM shows the same non-nuclear attractors that were later obtained by Sakata and Sato. This means that the non-nuclear attractors in silicon are really an artefact of the MEM. Key words: Maximum Entropy Method, non-nuclear attractors, charge density. X-ray diffraction.

Impaired cardiopulmonary response to exercise in moderate hypertension

OBJECTIVE

To identify the limiting factors of exercise performance in subjects with hypertension associated with left ventricular hypertrophy. The secondary objective was to establish relationship between peripheral function and exercise capacity.

DESIGN

Cardiopulmonary exercise testing was conducted using two protocols: a graded exercise test to maximal effort established maximal exercise capacity, followed by a step-incremental test combining gas-exchange measures and radionuclide angiography. The exercise responses were compared within and between groups.

SETTING

All hypertensive subjects were selected from the Toronto Tri-Hospital Hypertension Clinic. Normal subjects were recruited from the surrounding community.

PATIENTS

Twelve patients with established hypertension and left ventricular hypertrophy (determined by echocardiography) were studied as a referred/volunteer sample. All had no evidence of coincident diseases and were unmedicated at time of testing. A volunteer sample of normal, healthy subjects acted as a control.

INTERVENTIONS

Graded exercise to maximum and step-incremental (submaximal and steady-state) exercise was used to quantify cardiopulmonary function during exercise stress.

MAIN OUTCOME MEASURES

These included (for exercise performance) maximal oxygen intake (VO2max), the ventilatory anaerobic threshold, total peripheral resistance and blood lactate. Cardiac function measures included ejection fraction and ventricular volumes.

RESULTS

Cardiac function data obtained during exercise in hypertensive subjects included an increase in the pressure to volume ratio, but a blunted ejection fraction response at peak exercise (P less than 0.05). Although end-diastolic volume increased during exercise (P less than 0.05), values were lower during both levels of exercise compared with normal subjects. Mean +/- SD end-systolic volume increased from 39 +/- 22 at rest to 42 +/- 23 mL during peak exercise. Hypertensive subjects had a lower VO2 max (mean 27.4 +/- 4.8 mL/kg/min) compared with normals (40.0 +/- 8.5 mL/kg/min) and a lower ventilatory anaerobic threshold (14.4 +/- 2.9 versus 27.6 +/- 5.8 mL/kg/min, P less than 0.005). Furthermore, hypertensive patients had a significantly elevated total peripheral resistance at rest (2.5 +/- 1.0 versus 1.8 +/- 0.4 peripheral resistance units) and at peak exercise (1.6 +/- 0.7 versus 0.8 +/- 0.2, P less than 0.01) compared with normal subjects (P less than 0.05). A correlation coefficient of 0.92 was found between total peripheral resistance and VO2 max in hypertensive subjects (P less than 0.01).

CONCLUSIONS

These data suggest that peripheral factors, specifically a failure to reduce significantly total peripheral resistance, limits exercise performance despite a maintenance of left ventricular function during exercise in patients with moderate hypertension. The use of cardiopulmonary exercise testing can help in identifying the underlying cause of exercise intolerance in this population and limited left ventricular reserve at peak exercise, and may offer a sensitive measure of therapeutic end-points.

Cardiovascular responses to insertion of the laryngeal mask

We have compared, in 40 healthy patients, the cardiovascular responses induced by laryngoscopy and intubation with those produced by insertion of a laryngeal mask. Anaesthesia was induced with thiopentone and maintained with enflurane and nitrous oxide in oxygen; vecuronium was used for muscle relaxation. Arterial pressure was measured with a Finapres monitor. The mean maximum increase in systolic arterial pressure after laryngoscopy and tracheal intubation was 51.3% compared with 22.9% for laryngeal mask insertion (p less than 0.01). Increases in maximum heart rate were similar, (26.6% v 25.7%) although heart rate remained elevated for longer after tracheal intubation. We conclude that insertion of the laryngeal mask airway is accompanied by smaller cardiovascular responses than those after laryngoscopy and intubation and that its use may be indicated in those patients in whom a marked pressor response would be deleterious.

Cardiovascular and plasma catecholamine responses at tracheal extubation

The haemodynamic responses to tracheal extubation at the end of surgery were compared with those occurring at tracheal intubation in 12 patients undergoing major elective surgery. Arterial cannulation was performed and heart rate (HR), systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) were measured before induction of anaesthesia, before tracheal intubation, at the end of surgery and 1, 3 and 5 min after tracheal extubation. Laryngoscopy was avoided at the end of surgery. At all but the first of these stages, venous blood was obtained for measurement of plasma concentrations of adrenaline and noradrenaline. Rate-pressure product (RPP) was derived from SAP x HR. After tracheal intubation there were significant (P less than 0.05) increases in HR, DAP, RPP and in plasma concentrations of both adrenaline and noradrenaline. After extubation, only HR and adrenaline concentration at 5 min after extubation increased significantly compared with measurements at the end of surgery.

Nausea and vomiting with use of a patient-controlled analgesia system

The incidence of nausea and vomiting following patient controlled analgesia and intramuscular morphine injections on demand was compared in a double-blind randomised study of 32 healthy patients undergoing elective cholecystectomy. There were no significant differences between the two groups in mean 24 hour postoperative morphine consumption, subjective experience of pain, nausea and sedation assessed by visual linear analogue scoring, and the postoperative requirements for antiemetic therapy.

Serum bupivacaine concentrations following wound infiltration in children undergoing inguinal herniotomy

Serum bupivacaine concentrations were measured in 12 children who underwent elective herniotomy and who received analgesia in the form of wound infiltration. Mean (SD) peak concentration was 0.36 (0.14) micrograms/ml and time to peak concentration was 14.6 (7.2) minutes after infiltration of 1.25 mg/kg of bupivacaine. These concentrations are lower than those associated with other local anaesthetic blocks and well below potentially toxic levels. Wound infiltration provides a simple, effective and safe method of providing postoperative analgesia for hernia repair in children.

Wound infiltration of local anaesthetic after lower segment caesarean section

The analgesic efficacy of subcutaneous wound infiltration with 20 ml of 0.5% bupivacaine after elective lower segment section Caesarean section was studied in 28 patients in a double-blind randomised controlled manner using a patient-controlled analgesia system. The mean 24-hour morphine consumption of the placebo group and the bupivacaine group was similar (76 mg and 68 mg respectively). Analysis of the cumulative hourly morphine consumption failed to show any statistically significant differences between the groups. However, on a weight-adjusted basis statistically significant differences in morphine consumption were demonstrated, although these may not be clinically important. Subjective experiences of pain, nausea and drowsiness assessed by linear analogue scoring were similar in both groups.

A comparison of the effects of alfentanil/droperidol or fentanyl/droperidol on intra-ocular pressure

The influence of two intravenous sedative regimens on intra-ocular pressure was investigated in conjunction with retrobulbar local anaesthesia. Forty patients were allocated randomly to either group A (alfentanil and droperidol) or group F (fentanyl and droperidol). Measurements of intra-ocular pressure, arterial pressure and oxygen saturation were made before operation, after premedication, after intravenous sedation and after surgery. Paco2 was also measured before and after operation. Each sedation technique caused a similar reduction in intra-ocular pressure. There was less effect on Paco2 and oxygenation in group A.

Paediatric postoperative analgesia. A comparison of rectal diclofenac with caudal bupivacaine after inguinal herniotomy

Forty-three children for day case inguinal herniotomy under general anaesthesia were assigned randomly to receive either 1 ml/kg caudal bupivacaine 0.25% or rectal diclofenac 0.25 mg/kg intra-operatively to provide postoperative analgesia. Pain and demeanour were assessed by an observer in the early postoperative period after operation and by questionnaire for the parents over the first 24 hours. Caudal bupivacaine provided more pain-free patients at first but later the incidence of pain was similar in the two treatment groups. Rectal diclofenac is a useful alternative to caudal blockade in this group of patients.

Disruption of thymidylate synthesis and glycine-serine interconversion by L-methionine and L-homocystine in Raji cells

Excessive concentrations of L-methionine inhibited the folate-dependent de novo synthesis of thymidylic acid (TMP) in Raji cells, demonstrating the usefulness of this cell line for the study of methionine-folate antagonism. The effect was also produced by L-homocystine but not by other amino acids including D-methionine and L-ethionine, suggesting that this effect is exerted by a common intermediate of methionine and homocystine metabolism. L-Methionine, L-homocysteine, S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) are not inhibitors of thymidylate synthase activity. On the other hand the capacity of the cells to incorporate serine 3-carbon and glycine 2-carbon into DNA is impaired by the presence of L-methionine or L-homocystine. Studies with cell-free extracts demonstrated that the glycine cleavage enzyme is inhibited by 45% by L-methionine, L-homocysteine, SAM or SAH. Serine hydroxymethylase on the other hand was slightly stimulated by these sulfur-containing compounds and this stimulation was shown to occur in the intact cell as well. These findings suggest that when levels of L-methionine metabolites are elevated, there is an increase in the use of glycine to maintain the intracellular concentration of serine, which is required for homocysteine detoxification by conversion to cystathionine. The reduction in TMP synthesis caused by excess L-methionine or L-homocystine may result from increased utilization of one-carbon units for serine synthesis.