Derivation of level-specific reference change values (RCV) from a health screening database and optimization of their thresholds based on clinical utility

BACKGROUND

Reference change values (RCV) are used for judging the significance of changes between any two measurements. Based on the within-individual CV (CVI), RCV is conventionally computed as the 95% confidence limit (CL) of the changes: RCV=1.96×2CVI. $RCV = 1.96 \times \sqrt 2 C{V_I}.$ However, the appropriateness of assuming a constant CVI and using the 95% CL for RCV remains controversial.

METHODS

The level-specific CVI and RCV were estimated for 20 screening tests using a database composed of results from 13,545 health-screening attendees over a 17-year period, after preliminary exclusion of individuals taking medications or having unusual changes in body mass index (BMI). A rational CL for RCV was explored in reference to a clinical score for the metabolic syndrome, sMS, which was derived based on a logistic regression model consisting of tests related to metabolic syndrome. The effect of adjusting CL for the RCV on diagnostic efficacies of detecting between-year change in sMS was evaluated.

RESULTS

Test level dependency of CVI was apparent for some screening tests which have distributions with prominent skewing. The use of level-specific RCV was thus essential for them. The sensitivity for detecting a critical change in sMS based on the RCV set at 95%CL was extremely low in the majority of tests. However, by lowering CL stepwise from 95 to 75%, the sensitivity improved greatly without much change in specificity and positive predictive value. Loss-and-gain analysis showed that CL for RCV set around 80% gave the lowest loss, assuming a policy of reducing false negative judgment.

CONCLUSIONS

Level specific CVI and RCV were necessary in tests with skewed distributions. RCV using 80%-90% CL is suitable in health screening for diseases that require early intervention for changes.

Anticoagulant management of atrial fibrillation: the influence of dosing algorithm and recall schedule on time in therapeutic range

BACKGROUND

The quality of anticoagulation management in atrial fibrillation patients is reflected by the concept of time spent in therapeutic range (TTR). In a primary care setting, the implementation of a dose nomogram could help increase the mean TTR among these patients.

OBJECTIVE

This study compares the influence of a dose algorithm with an integrated recall on TTR prior to standard care and after the implementation of the protocol.

PATIENTS AND METHODS

In a purposive sample of patients with AF, an uncontrolled 'before' and 'after' study design was utilized to measure the effects of the protocol on TTR. Demographic data, TTR levels, frequency of international normalized ratio (INR) within therapeutic range, clinician adherence to dose nomogram and warfarin dose changes were captured from consultations at the anticoagulation clinic.

RESULTS

A total of 152 patients with AF were entered into the final analysis. The increment in mean TTR in the 'after' intervention phase (2.9%) was not statistically significant (57.5-60.4%, P=0.252). The increase in the frequency of INR values within therapeutic range in the 'after' intervention phase was significant (50.0-56.0%, P<0.05) but with a very low effect size (r=0.04).

CONCLUSIONS

The implementation of a dose nomogram has the potential of reducing unnecessary dose changes for minor fluctuations in INR levels. The findings in this study needs to be confirmed in a future study involving other indications for anticoagulation, various regional primary care clinics and a larger population size.

New Approach for Interpreting Changes in Circulating Tumour Cells (CTC) for Evaluation of Treatment Effect in Metastatic Breast Cancer

Aim: Attempts have been made to use CTC values for interpretation of treatment response and to guide change of chemotherapy by using a static cut-off of 5 CTC to stratify patients in favourable or unfavourable responders. We propose a new approach to interpret treatment effect using significant changes in CTC values (SCV-limits1) as grouping parameter for responders and non-responders to chemotherapy among metastatic breast cancer (mBC) patients. Method: CTC were analysed using the CellSearch System in blood from 47 mBC patients before the start of new chemotherapy and before the third cycle of therapy. The new and old approach to interpret changes in CTC values were compared in relation to progression free survival (PFS). Results: The new approach using significant CTC change (P = .032) and the old approach using static cut-off (P > .001) correlated significantly with PFS using a cohort of 47 patients. Conclusion: We propose a new approach to interpret significant changes between baseline and follow-up CTC values as a tool for assessing treatment effect in mBC. Our approach stratified patients in new risk groups that were stratified significantly with respect to PFS. More patients are needed to balance the size of the risk groups for better comparison to the existing approach based on a 5 CTC cut-off.

The influence of coagulation factors on the in-treatment biological variation of international normalized ratio for patients on warfarin

BACKGROUND

Biological variation is usually estimated in healthy individuals during steady-state conditions. The aim of this study was to estimate the in-treatment biological variation of the International normalised ratio (INR) and to investigate to what extent the different levels of coagulation factors could explain this variation.

METHODS

Blood samples were collected from randomly included patients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact(®)) and on three point-of-care instruments (Simple Simon(®)PT, CoaguChek(®)XS and INRatio(™)). The level of fibrinogen, and the activity of coagulation factors II, V, VII and X were determined.

RESULTS

The in-treatment within- and between-subject coefficients of variation of INR were dependent on the method and varied between 18 and 24% and 13 and 19%, respectively, and were reduced to 3.9-5.1% and 2.3-5.8%, after correction for coagulation factors which could explain 91-95% of the variance of INR.

CONCLUSIONS

The in-treatment biological variation of INR was higher than reported for healthy individuals as well as patients in a steady-state condition, but by correcting for appropriate coagulation factors it was reduced. The association between INR and coagulation factors was different for the different PT methods mainly due to different sensitivity towards FII and FVII.

Improvement of anticoagulant treatment using a dynamic decision support algorithm: a Danish Cohort study

INTRODUCTION

Warfarin is the most widely prescribed vitamin K antagonist and in the United States and Europe more than 10 million people are currently in long-term oral anticoagulant treatment. This study aims to retrospectively validate a dynamic statistical model providing dosage suggestions to patients in warfarin treatment.

MATERIALS AND METHODS

The model was validated on a cohort of 553 patients with a mean TTR of 83%. Patients in the cohort were self-monitoring and managed by a highly specialised anticoagulation clinic. The predictive model essentially consists of three parts handling INR history, warfarin dosage and biological noise, which allows for prediction of future INR values and optimal warfarin dose to stay on INR target. Further, the model is based on parameters initially being set to population values and gradually individualised during monitoring of patients.

PRIMARY OUTCOME

Time in therapeutic range was used as surrogate quality measure of the treatment, and model-suggested dosage of warfarin was used to assess the accuracy of the model performance.

RESULTS

The accuracy of the model predictions measured as median absolute error was 0.53 mg/day (interquartile range from 0.25 to 1.0). The model performance was evaluated by the difference between observed and predicted warfarin intake in the preceding week of an INR measurement. In more than 70% of the cases where INR measurements were outside the therapeutic range, the model suggested a more reasonable dose than the observed intake.

CONCLUSION

Applying the proposed dosing algorithm can potentially further increase the time in INR target range beyond 83%.

CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability in patients on long-term anticoagulation

OBJECTIVES

The main aim of this study was to determine whether CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability during initial dose-finding phase and during maintenance treatment after 360 days.

METHODS

Two hundred and six consecutive patients who were beginning warfarin therapy were selected. They were assessed for general and clinical characteristics; prescribed warfarin dose; response to therapy on days 7-10, 30, 60, 180, and 360; adverse events; and CYP2C9 2, 3, 5, 6, 8, 11, and VKORC1 1639G >A assays.

RESULTS

During the first 30 days of anticoagulation, the relative variability of warfarin dose was significantly associated with CYP2C9*2 and CYP2C9*3 polymorphisms (p = 0.02) and with VKORC1 1639G >A genotypes (p = 0.04). Warfarin variability was also statistically different according to predicted metabolic phenotype and to VKORC1 genotypes after 360 days of treatment, and in the phase between 180 and 360 days (long-term dose variability). Both CYP2C9 and VKORC1 polymorphisms were associated with the international normalized ratio (INR) made between 7 and 10 days/initial dose ratio, adjusted for covariates (p < 0.01 and p = 0.02, respectively). Patients carrying VKORC1 and CYP2C9 variants presented lower required dose (at the end of follow-up of 360 days) compared to patients carrying wild-type genotypes (p = 0.04 and p = 0.03, respectively).

CONCLUSIONS

Genetic information on CYP2C9 and VKORC1 is important both for the initial dose-finding phase and during maintenance treatment with warfarin.

Telemedicine improves the monitoring process in anticoagulant treatment

We compared the INR (International Normalized Ratio) monitoring process using a telemedicine device with the conventional approach in which blood samples were sent to the hospital for analysis. We conducted a randomized controlled trial. We enrolled 40 patients on chronic warfarin therapy from two primary healthcare centres (PHCs). Half were monitored using the telemedicine device and half were monitored conventionally. Each patient received three INR measurements. The total processing time was measured from blood sampling until warfarin dosing was performed in the anticoagulant clinic. The median total processing time was significantly shorter with telemedicine than usual care (34 vs. 260 min, P < 0.001). This was mainly because sample transport was avoided using the point-of-care device and automatic data transmission. Telemedicine reduced the total processing time for INR monitoring and has the potential to improve the management of patients undergoing anticoagulant treatment at PHCs.

Biological variation of INR in stable patients on long-term anticoagulation with warfarin

Within-individual biological variation of INR (CV(B)) was assessed in 245 selected stable warfarin-treated patients monitored by three thrombosis centers. Selection criteria were: treatment period of six months or longer before the observation period; at least six consecutive INRs within the therapeutic range of 2.0 - 3.0; interval between consecutive INR measurements of two weeks or longer; no change in warfarin dose; no changes in the patient's circumstances which may influence the INR, such as intercurrent diseases, invasive procedures, starting or stopping drugs interacting with warfarin. The minimum, maximum and mean within-individual coefficient of variation CV(B) of the INR measurements in the 245 selected patients were 0.4%, 14.5%, and 9.0%, respectively Analytical performance goals for the INR measurement (imprecision) could be derived from the mean CV(B). For a therapeutic range of 2.0 - 3.0 with warfarin, the desirable and optimum imprecision of INR determination is <4.5% CV and <2.25% CV, respectively. The biological variation and analytical performance goals have been derived using classic laboratory methods but should be applicable to point-of-care testing as well.

Discard first tube for coagulation testing

Tissue thromboplastin may contaminate the first tube sample due to the trauma of the venipuncture, and therefore, affect the accuracy of coagulation testing. This practice was stopped by Clinical and Laboratory Standards Institute after several studies. However, most of the studies have verified these conclusions and refuted the need for a discard tube when drawing samples for coagulation tests in healthy groups. The purpose of our study was to evaluate the clinical importance of discarding a tube for prothrombin time (PT) determinations on large samples with international normalized ratio (INR) values between and over targeted therapeutic range. Patients receiving oral anticoagulation therapy (OAT) managed by our cardiology service were selected for this study. Tube 1 was always treated as the discard tube. Tube 2 was allocated to be analyzed along with the tube 1 for coagulation tests. Individual values were grouped into four cohorts according to the INR range. The ranges were as follows: less than 2.0, 2.1-3.0, 3.1-4.5 and more. Three hundred and seventy-six samples were drawn for PT/INR and activated partial thromboplastin time testing. We found statistically significant differences between tube 1 and tube 2 (P < 0.05), and satisfactory correlation coefficients were obtained by linear regression analysis (0.86 or greater in all cases). This study consisted of a high number of samples. Our data suggest that drawing a discard tube is still necessary for coagulation testing. Consideration should be given to revising the international guidelines related to the necessity of a discard tube for repeated evaluation of coagulation tests especially receiving long-term OAT.

Precision and accuracy of point-of-care testing coagulometers used for self-testing and self-management of oral anticoagulation therapy

BACKGROUND

Oral anticoagulation therapy is monitored by the use of the International Normalized Ratio (INR). Patients who perform self-testing or self-management use a point-of-care testing (POCT) coagulometer (INR monitor) to estimate their INRs. A precondition for a correct dosage of coumarins is a correct INR estimation, and the method and apparatus used for providing the INR measurements are crucial in this context. Several studies have been published regarding the precision and accuracy of these POCT coagulometers, and have led to diverse conclusions. It is difficult and challenging to perform an overview of the literature, owing to the vast amount of papers, with differences in design, statistical analysis, etc.

OBJECTIVES

The aim of this systematic review was to analyze the current literature, especially regarding the precision and accuracy of the POCT coagulometers, to provide recommendations for clinical use and quality control, and to point out areas for future research.

METHODS

We included a total of 22 studies, of which four were characterized as high-quality studies.

RESULTS

The precision of the POCT coagulometers was generally adequate for clinical use. Their performance in terms of accuracy has to be viewed in the context of the inherent inaccuracies of INR measurements.

CONCLUSIONS

The accuracy of POCT coagulometers seems, in this respect, to be generally acceptable, and they can be used in a clinical setting.

Within-subject biological variation of glucose and HbA(1c) in healthy persons and in type 1 diabetes patients

BACKGROUND

Several articles describing within-subject biological variation of fasting glucose and HbA(1c) in healthy populations have been published, but information about biological variation of glucose and HbA(1c) in patients with type 1 diabetes is scarce. It is reasonable to assume that type 1 diabetics differ from their healthy counterparts in this matter. The aim of our study was to estimate the biological variation of glucose and HbA(1c) in healthy subjects and in patients with type 1 diabetes.

METHODS

Fifteen healthy individuals and 15 type 1 diabetes patients were included. Biological variations were calculated based on blood samples collected weekly for 10 consecutive weeks from the healthy and the eligible of the type 1 diabetes patients.

RESULTS

The within-subject variations of glucose were approximately 5% in healthy individuals and 30% in diabetes patients, and for HbA(1c) they were 1.2% in healthy individuals and 1.7% in diabetes patients.

CONCLUSIONS

In conclusion, we found a high within-subject biological variation of glucose in diabetes patients as expected compared to healthy individuals (30% vs. 5%). The short-term (2 months) within-subject biological variation of HbA(1c) did not differ significantly between well regulated type 1 diabetes patients and healthy individuals (1.7% vs. 1.2%).

Urgent reversal of vitamin K antagonist therapy

In the developed world, an increasing number of patients receive therapy with vitamin K antagonists (VKA). This group of patients poses an additional challenge in the perioperative management of emergency surgery and trauma. The present review offers a detailed description of some treatment options for reversal of VKA therapy. Optimal treatment of the anticoagulated patient requires a well-balanced intervention securing a reduced risk of haemorrhagic surgical complications as well as optimal anticoagulation post-operatively without exposing the patient to an increased risk of thromboembolic complications. The following factors must be considered in VKA-treated patients scheduled for emergency surgery: (1) the indication for VKA therapy, including the risk of thromboembolic events when the International normalized ratio (INR) is reduced, (2) type of surgery, including the risk of haemorrhagic complications and (3) the pharmacodynamic/-kinetic profile of the therapy used to revert the VKA therapy. Therapeutic options for acute reversal of VKA therapy include: vitamin K, fresh frozen plasma (FFP), prothrombin complex concentrate (PCC) and perhaps activated recombinant factor VII. PCC is a relatively new drug in some European countries and clinical experience is limited compared with the use of FFP. Reversal of VKA anticoagulation with PCC is faster and more efficient compared with FFP, but there are currently no randomized studies demonstrating an improved clinical outcome.

Home management of oral anticoagulation via telemedicine versus conventional hospital-based treatment

BACKGROUND AND OBJECTIVE

We have developed an expert computer system for the control of oral anticoagulation therapy, accessible by the patients via their own computer. To investigate if the weekly measurement and dosing of international normalized ratio (INR) at home using the online Internet-based system was superior to conventional treatment, we performed a randomized, controlled trial.

PATIENTS AND METHODS

All 669 patients in our anticoagulation clinic were asked to participate in the trial, providing that they had Internet access and could use the CoaguChek XS system. A total of 140 patients were included and randomized to (A) once weekly measurement and report online, (B) twice weekly measurement and report online, and (C) continued conventional treatment with INR measurement in the lab every 4 weeks and dose adjustment by letter.

RESULTS

Group A had 79.7% (95% CI 79.0-80.3) of time in therapeutic range (TTR), group B 80.2% (95% CI 79.4-80.9) of TTR, and group C 72.7% (95% CI 71.9-73.4) TTR. Groups A and B perform statistically significantly better than the conventional group C, with a difference of TTR of 7% points (p < 2.2 × 10(-16)), whereas no difference was seen between A and B.

CONCLUSION

Home measurement of INR and the reporting and dosing of results online once a week increase TTR from 72% to 79% as compared to conventional computer-assisted monitoring in an anticoagulation clinic.

Interaction between acetaminophen and warfarin in adults receiving long-term oral anticoagulants: a randomized controlled trial

PURPOSE

We investigated whether acetaminophen, given at 2 g/day and 3 g/day might potentiate the anticoagulant effect of warfarin.

METHODS

Forty-five patients on stable warfarin therapy, enrolled in this prospective, randomized, parallel (three arms), placebo-controlled study, received a 10-day regimen of acetaminophen (2 g/day or 3 g/day) or placebo.

RESULTS

The mean maximal INR increase was 0.70 ± 0.49 and 0.67 ± 0.62 in patients receiving acetaminophen at 2 g/day and 3 g/day, respectively (P=0.01 for the respective comparisons versus placebo). The INR increase became significant on day 3 and was independently and significantly predicted by a maximal decrease in factor II (R(2)=0.36, P<0.0001), factor VII (R (2)=0.46, P<0.0001) and a maximal increase in acetaminophen plasma concentrations (R(2)=0.563, P<0.0001).

CONCLUSION

Acetaminophen, at 2 g/day or 3 g/day, enhanced the anticoagulant effect of warfarin in stable patients, thus requiring close INR monitoring in the clinical setting.

Point-of-care INR measurement in children requiring warfarin: what has been evaluated and future directions

Many children are surviving primary illnesses and now require thromboprophylaxis as a result of advances in management. Vitamin K antagonists are commonly prescribed to prevent or treat thrombosis. These agents are far more challenging to effectively manage in children. As a result of these challenges, frequent blood monitoring to measure international normalized ratio (INR) values is required. Point-of-care (POC) INR monitors use a capillary blood sample that has been expressed as a solution to improve effective management of vitamin K antagonist therapy. POC INR meters have been demonstrated to be accurate and precise in measuring INRs. Implementation of a standardized education program prior to patient use of POC meters results in differences between measured laboratory INRs and POC INR comparisons that meet criteria for clinical relevance. This indicates that POC INR meters are safe and effective for use in children.

Evaluación de un programa de seguimiento de pacientes ancianos institucionalizados en tratamiento con anticoagulantes orales

OBJECTIVE

To assess an interdisciplinary follow-up programme for institutionalised elderly people on oral anticoagulant treatment.

METHOD

The proposed follow-up treatment is of an interdisciplinary nature and includes INR, an interview with the patient and/or carer and an assessment of the treatment plan every week. The quality of drug treatment is assessed by the percentage of time and the percentage of measurements falling within the therapeutic range. The suitability of the programme in comparison to the traditional follow-up was studied in terms of the different proportions for the first variable and by analysing contingency tables for the second.

RESULTS

Nine patients were recruited. Six patients (67%) showed a significant increase in the percentage of time they remained within the therapeutic range. 68.5% of INR measurements during the follow-up programme were within therapeutic range. The percentage of INR measurements below the therapeutic range was significantly reduced when compared to the traditional follow up. Thirteen pharmaceutical interventions were documented per patient.

CONCLUSIONS

The complexity of oral anticoagulant treatment, the large number of interventions carried out together with elderly patients poor treatment compliance are evidence of the need to introduce follow-up programmes which include the professionals responsible for the patients care.

Managing transferability of laboratory data

Considerable attention has been focused on definition and enhancement of the analytical quality in laboratory testing over the past decades. Advances in laboratory technology and computer informatics have allowed a major sense of confidence with the analytical phase and more efforts should now be focused on extra-analytical areas of improvement, that should further strengthen the link between cost effectiveness and clinical outcome. Deduction and implementation of common reference intervals, to be possibly shared by a regional network of clinical laboratories, appear so far a crucial step to increase efficiency and harmonization. With the experience gained from External Quality Control exercises and with the consensus of several contributory laboratories, this process is underway in Italy. Quality performances resulting from widespread implementation of common reference intervals and longitudinal comparison of patient's data, will allow clinical laboratories to accomplish with a major transferability, amplifying health benefits and meeting increasing health systems demand.

Paracetamol: a haemorrhagic risk factor in patients on warfarin

AIM

To quantify the effect of paracetamol on the anticoagulant effect of warfarin under normal clinical conditions.

PATIENTS AND METHODS

In a prospective double-blind, cross-over, placebo-controlled study, 11 patients on stable warfarin therapy received in random order two 14-day regimens of paracetamol 4 g day(-1) or placebo, with a 14-day or more wash-out period in between, time necessary to fulfil the inclusion criteria.

RESULTS

In patients on paracetamol, the mean maximum increase in the International Normalized Ratio (INR) observed was 1.04 +/- 0.55 vs. 0.20 +/- 0.32 in those on placebo (P = 0.003). The mean maximum INR observed was significantly higher with paracetamol than with placebo (3.47 vs. 2.61, P = 0.01). In patients receiving paracetamol, the mean observed INR was significantly increased after 4 days (+ 0.6 +/- 0.6, P < 0.001).

CONCLUSION

Paracetamol at 4 g day(-1) induces a significant increase in INR in patients receiving a stable regimen of warfarin, increasing the risk of bleeding associated with warfarin.

Significance of consecutive international normalized ratio (INR) outcomes using statistical control rules in long-term anticoagulated patients. Optimization of laboratory monitoring and interpretation of borderline measurements

Analysis of serial measurements is needed to elaborate observations in all fields of medical research. In the present study, retrospective data of anticoagulated patients were used to calculate a mean of observations and control limits, X+/-1sigma and X+/-2sigma (mean+/-standard deviation). During 18 months of coagulation monitoring, 45 patients without major oral anticoagulant therapy complications, with more international normalized ratio (INR) determinations in the therapeutic range and with a normal distribution of INR values according to the Kurtosis coefficient, were selected. The cumulative distribution functions allowed us to obtain critical limits of INR with a cumulative probability (p). Control limits, calculated for a therapeutic control chart, indicated through different control rules, 1S2 or 2S1, an alarm signal to analyze the cause of INR outside the therapeutic range. Our investigation suggested that for results at the level of the therapeutic control limits, we needed at least two consecutive INR results to detect a significant over- or under-anticoagulation. The therapeutic control chart method should be a useful means in clinical practice for evaluating the statistical significance of consecutive and borderline INR outcomes. Analytical improvements and control rules applied to laboratory monitoring may help optimize drug dose administration.

Antithrombotic agents: implications in dentistry

Thrombosis and the complicating emboli that can result are important causes of illness and death. Thrombosis is of greater overall clinical importance in terms of morbidity and mortality than all of the hemorrhagic disorders combined. Agents such as heparin, low-molecular weight heparin, warfarin, aspirin, ticlopidine, clopidogrel, and tirofiban are used to prevent venous or arterial thrombosis. Patients taking these antithrombotic agents may be at risk for excessive bleeding after invasive dental procedures. The current antithrombotic agents used in medicine are reviewed, and the dental management of patients taking these agents is discussed.

How to assess the relative range of two consecutive laboratory measurements to monitor patients

An integral part of routine health checkups involves laboratory measurements on various analytes in the blood. It is then common to compare the value of two consecutive measurements sampled at different times from the same patient. A "significant" change requires an action (additional sample and/or clinical action). The current rule is to check whether the relative range of measurement is larger than a certain critical threshold. This rule should guarantee a specified confidence level (e.g., 95%), but its derivation was based on an approximation. We derive the exact distribution and show that it is related to the doubly noncentral F distribution. The currently used threshold values are compared with the exact ones, and some limited power calculations are presented to detect changes in the patient condition.

Reliability of delayed prothrombin time INR determinations in a central laboratory using off-site blood sampling

A major concern of centralized anticoagulant measurements with off-site sampling is the reliability of international normalized ratio (INR) determinations on blood that may have been taken from the patient hours before the analysis. We compared INR differences in the blood of patients receiving oral anticoagulants after 24 h storage in four conditions: centrifuged at room temperature, centrifuged at 4 degrees C, uncentrifuged at room temperature and uncentrifuged at 4 degrees C. The INR of centrifuged and uncentrifuged blood left at room temperature for 24 h consistently increased by 6% and, after adjustment, there were no misclassifications in the assessment of the adequacy of anticoagulant treatment. Inconsistent changes were noted in tests of refrigerated centrifuged blood. We conclude that storage of blood at room temperature for 24 h results in a consistent prolongation of the prothrombin time, which after correction can reliably be used to adjust the dose of oral anticoagulants.

Diagnosis and Monitoring of Hepatic Injury. I. Performance Characteristics of Laboratory Tests

Purpose: To review information on performance characteristics for tests that are commonly used to identify acute and chronic hepatic injury.

Data Sources and Study Selection: A MEDLINE search was performed for key words related to hepatic tests, including quality specifications, aminotransferases, alkaline phosphatase, γ-glutamyltransferase, bilirubin, albumin, ammonia, and viral markers. Abstracts were reviewed, and articles discussing performance of laboratory tests were selected for review. Additional articles were selected from the references.

Guideline Preparation and Review: Drafts of the guidelines were posted on the Internet, presented at the AACC Annual Meeting in 1999, and reviewed by experts. Areas requiring further amplification or literature review were identified for further analysis. Specific recommendations were made based on analysis of published data and evaluated for strength of evidence and clinical impact. The drafts were also reviewed by the Practice Guidelines Committee of the American Association for the Study of Liver Diseases and approved by the committee and the Association’s Council.

Recommendations: Although many specific recommendations are made in the guidelines, some summary recommendations are discussed here. Alanine aminotransferase is the most important test for recognition of acute and chronic hepatic injury. Performance goals should aim for total error of &lt;10% at the upper reference limit to meet clinical needs in monitoring patients with chronic hepatic injury. Laboratories should have age-adjusted reference limits for enzymes in children, and gender-adjusted reference limits for aminotransferases, γ-glutamyltransferase, and total bilirubin in adults. The international normalized ratio should not be the sole method for reporting results of prothrombin time in liver disease; additional research is needed to determine the reporting mechanism that best correlates with functional impairment. Harmonization is needed for alanine aminotransferase activity, and improved standardization for hepatitis C viral RNA measurements.

Components of biological variation of biochemical markers of bone turnover in Paget's bone disease

The aims of this study were to evaluate the components of biological variation of the new markers of bone turnover in patients with Paget's bone disease and to compare the results with data obtained in healthy subjects. Fifteen patients with Paget's disease in a stable period of the disease and 12 healthy premenopausal women were included for a 1 year follow-up study. Within- and between-subject biological variation, indices of individuality, and critical differences were evaluated for the following biochemical markers: in serum, total (tAP), and bone (bAP) alkaline phosphatases, procollagen type I N-terminal propeptide (PINP) and beta-carboxyterminal telopeptide of type I collagen (sCTx); in urine, hydroxyproline (Hyp), and amino (NTx) and beta-carboxyterminal (CTx) telopeptides of collagen type I. Serum markers of bone turnover showed lower biological variability than urinary markers. Within-subject biological variation was higher in pagetic patients than in healthy subjects for all serum markers. In both groups, bAP presented the lowest within-subject biological variation. In pagetic patients, all markers presented indices of individuality of <0.6, indicating their usefulness for patient monitoring. Critical differences were lower for serum markers than for urinary markers. Among pagetic patients, serum bAP and PINP showed the lowest critical differences with values close to 30%, whereas urinary CTx presented the highest critical differences (near 70%). Conversely, in healthy subjects, tAP was the marker with the lowest critical differences, being two-fold higher in pagetic patients. This study confirms the lower sensitivity of urinary markers to detect significant changes and indicates that data obtained on biological variations from healthy populations cannot always be extrapolated to pathological conditions. In addition, serum bAP and PINP seem to be the markers that best reflect a significant change in activity of Paget's disease.

Evaluation of a simple dosage scheme for transition from phenprocoumon to warfarin in oral anticoagulation

Phenprocoumon, whose elimination half-time is 144 hours, has been the traditional oral anticoagulant of choice in Europe. However, today's most widely used drug is warfarin, whose elimination half-time is 40 hours. This study aims to evaluate a method for safe transition from phenprocoumon to warfarin, which is sometimes required. Hence, the large difference in their elimination rates may on occasion lead to serious overdosage upon transition from one drug to the other. According to average equipotent doses, a stepwise increase in warfarin dose was calculated based on the elimination half-times of the two drugs. The dosage scheme was subsequently tested in a pilot study including 35 patients. The conversion scheme was then adjusted based on the results from the pilot study. The new scheme was tested in 69 patients. The transition factor was 2.3, which implies that equipotency was achieved when the warfarin dose was 2.3 times larger than the phenprocoumon dose (in mg). This scheme proved optimal for 75% of the patients. However, the dose had to be adjusted individually in the remaining 25% of the patients to a level corresponding to the measured international normalised ratios. No patients experienced haemorrhages or thromboembolic complications during the period of changeover. In conclusion, the proposed scheme for changing medication from phenprocoumon to warfarin is safe and convenient.

Graphical interpretation of analytical data from comparison of a field method with a Reference Method by use of difference plots

Various viewpoints have been offered regarding the appropriate use of scatter plots or difference plots (bias plots or residual plots) in comparing analytical methods. In many of these discussions it seems the basic concepts of identity (within inherent imprecision) and acceptability based on analytical goals (analytical quality specifications) have been forgotten. With the increasing number of Reference Methods in laboratory medicine, these basic concepts are becoming more important in validation of field methods. Here we describe a simple and effective graphical test of these hypotheses (identity and acceptability) by use of difference plots. These plots display the underlying hypothesis before the measured differences are plotted and allow interpretation of the results according to specific criteria. We further describe simple but effective interpretations of the data, when the hypothesis is not fulfilled, by using two data sets drawn from comparisons of field methods for S-creatinine with a Reference Method for this analyte. The difference plot is a graphical tool with related simple statistics for comparison of a field method with a Reference Method, focusing on (a) identity within the inherent analytical imprecision or (b) acceptability within analytical quality specifications. Calculation of the standard deviation of the differences is an indispensable tool for evaluation of aberrant-sample bias (matrix effects).

Biological variation of International Normalized Ratio for prothrombin times, and consequences in monitoring oral anticoagulant therapy: computer simulation of serial measurements with goal-setting for analytical quality

Oral anticoagulant therapy (OAT) has a well-established efficacy in prophylaxis and treatment of thromboembolic disorders. Because complications are related to intensity of OAT, optimal control of treatment is mandatory. In studies of OAT, as many as 30% of International Normalized Ratio (INR) measurements for prothrombin times fall outside the therapeutic interval. Preanalytical, analytical, and biological variation all contribute to this. Computer simulations of serial INR measurements were performed for various assumed in-treatment setpoints within the therapeutic interval INR 2.0–3.0 and for an “in-treatment within-subject variation” (CV) of 10.1%. Results are presented in difference plots with therapeutic intervals and critical differences. If the in-treatment setpoint is mid-interval (INR = 2.5), only 5% of simulated INR values fall outside the therapeutic interval. Setpoints deviating from the mid-interval and increases in the in-treatment within-subject variation considerably increase the number of observations outside the therapeutic interval and the critical differences. In conclusion, random variation, biological or analytical, and setpoints (targets) deviating from mid-interval explain a substantial number of the INR values outside therapeutic intervals observed in clinical studies. Analytical imprecision should be kept &lt;5% and analytical bias &lt;±0.2 INR.

Relationship between prothrombin activation fragment F1.2 and international normalized ratio in patients with atrial fibrillation. Stroke Prevention in Atrial Fibrillation Investigators

BACKGROUND AND PURPOSE

The prothrombin time (expressed as the international normalized ratio [INR]) is the standard method of monitoring warfarin therapy in patients with atrial fibrillation. Prothrombin activation fragment F1.2 provides an index of in vivo thrombin generation and might provide a better index of the effective intensity of anticoagulation. We examined the relationship between F1.2 and INR in patients with atrial fibrillation.

METHODS

We measured INR and F1.2 levels in 846 patients with atrial fibrillation participating in the Stroke Prevention in Atrial Fibrillation III study. Two hundred nineteen (26%) were taking aspirin alone, 326 (39%) were taking adjusted-dose warfarin, and 301 (36%) were taking a low fixed dose of warfarin (1 to 3 mg) plus aspirin (combination therapy). F1.2 levels were measured with an enzyme-linked immunosorbent assay.

RESULTS

Patients receiving adjusted-dose warfarin or combination therapy had significantly higher INR and significantly lower F1.2 values than those on aspirin alone (P < or = .0001 for each of the four comparisons). F1.2 values (nanomolar) were inversely correlated with INR (F1.2 = -0.1 + 2.3[1/INR]; R2 = .37; P < .0001; simple linear regression). However, significant variability remained. Among patients receiving warfarin, older patients had higher F1.2 values than younger patients after adjustment for INR intensity (P < .001) in the model. There was no difference in the relationship between F1.2 and INR between men and women.

CONCLUSIONS

Increasing intensity of anticoagulation, as measured by the INR, is associated with decreasing thrombin generation as measured by the F1.2 level, but significant variability exists in this relationship. Older anticoagulated patients have higher F1.2 values than younger patients at equivalent INR values. The clinical significance of these differences is not clear. F1.2 measurement might provide information regarding anticoagulation intensity in addition to that reflected by the INR.