Welcome to the AACC Expert Access Live Online program.

Our topic this month is Point-of-Care Coagulation Monitoring . This rapidly growing field has come far from the days where ACTs were performed in the operating room and cardiac catheterization laboratories with little oversight, and it now includes aPTT , PT and specialty applications. This edition of Expert Access will familiarize the participant with the wide variety of tests and analyzers currently available. Differences and similarities between these systems will be explored as well as defining realistic expectations for comparisons to central laboratories. There is also a brief description of the regulatory issues surrounding point of care coagulation monitoring View the presentation and direct your questions to this month's online expert, Marcia Zucker, PhD, Director of Clinical Affairs for International Technidyne Corporation (Edison, N.J.).

AACC would like to extend its most sincere thanks to the Bayer Corporation for making this program possible.

Our facility is considering a "coagulation clinic" to serve patients who are on long-term anticoagulation therapy. Do these POCT devices work as well in this setting vs. an inpatient setting? Has anyone looked into home-use patient self-testing for those who must moitor their therapy?
Dallas, TX

Marcia L. Zucker, Ph.D.:Yes and yes. Actually, the POC PT/INR devices are used more frequently in oral anticoagulation clinic (OAC) settings than in inpatient areas as the advantages of these systems in using fingerstick samples and the rapid turn around time allow improved efficiency in the OAC environment. There have been many publications over the years specifically describing the value of POC testing in OACs. Patient self-testing (PST) is a rapidly growing application for these monitors. This past summer CMS approved Medicare reimbursement of patients with mechanical heart valves. PST testers also include patients with many other indications. These patients are, by definition, only a subset of those requiring long-term oral anticoagulation, as they must be highly compliant. A detailed evaluation of the use of POC testing for PT/INR measurement will soon be presented on line through the AACC POCT Division Distance Learning Program.

You touched on this briefly in one of your later slides, but can you expound a little on the connectivity issue. Are there any special considerations or difficulties that one wouldn't encounter with other POCT devices?
Boston, MA

Marcia L. Zucker, Ph.D.:The only difficulty that might be unique to these devices is the wide variety of test options each system offers. Unlike most (but certainly not all) other POC systems in use, each coagulation system available has a different test menu and can display results in a unique manner. A quick look at slides 8 through 12 will clarify this issue. In addition, some of the systems (i.e. Hemochron 401, 801, Medtronic HMS, ACTII) have been available for more than 20 years. These systems were not designed with connectivity and therefore would need to be upgraded to more recent versions or require special adapters to allow connectivity.

While using Roche's CoaguCheck, there are from time to time changes in INR reference values announced by the manufacturer. These changes are generally given only for the "normal" population. Special populations, like the one with cardiac valves, seem not to be concerned by this changes. Is that correct or is this an omission by the manufacturer? Stefano Longoni, Ph.D, Specialist in laboratory medicine FAMH Institut Dr. Viollier Basle, Switzerland
Basle, Switzerland

Marcia L. Zucker, Ph.D.:As far as I am aware, the value that changes when using the CoaguChek system is the lot specific ISI. This value is encoded on the code chip that is supplied with the test strips to ensure appropriate INR calculations. I do not know of changes in the INR reference ranges, either for a normal population or a specific patient group. It might be best to contact someone at Roche with specific questions regarding their system.

We do ACT testing on the Hemachon Jr. We have 6 Hemachrons in our hospital (which we cannot take out of service all at the same time). CAP requires that correlation between instruments be performed over the reportable range. Currently we are using 2 points from the ACT linearity procedure (citrated whole blood to which heparin, then CaCl is added. Is this acceptable?
Springfield, Ohio

Marcia L. Zucker, Ph.D.:Using a 2-point check may not be sufficient as the requirement states “over the reportable range”. I cannot answer for CAP, of course, but I can describe the procedures used by many facilities to comply with this requirement. In a situation like this, sites frequently rely on a split sample clinical comparison. Two or three instruments will be brought to a single clinical location where the same tests are used, for example a critical care or dialysis instrument may be brought to the cath lab. Split patient samples are then run across these instruments to show correlation. The instruments are then returned to their regular locations and other instruments are brought into those sites for further comparison. In this way, without bringing all 6 instruments to a single location simultaneously, the comparisons can still be made. Instruments B and C correlate with instrument A. Instruments D and E correlate with instrument C, so they must correlate also with instruments B and A. I have spoken to individuals who do this sort of comparison every six months and have had no problem during CAP inspections.

Dr. Zucker I am interested in finding out if your team along with performance analysis did you look at cost benefits in terms of outcome and patient management. If so how did you do it?
Toronto, Canada

Marcia L. Zucker, Ph.D.:There are published studies which address both patient outcome and cost benefits for POC coagulation testing. Some have been sponsored by ITC, but many are from other corporate sponsors or are independent investigations. How these are set up depends on the specific clinical application of interest. Cardiac surgery studies have the most clearly defined patient outcome measures, intra- and post-operative blood loss and transfusion requirements. These patients can then be followed further to examine complication rates and re-exploration. The financial benefits are generally calculated secondary to patient outcome. Studies in interventional cardiology often look at thrombus formation and re-occlusion as short-term outcome indicators. Time to stabilization has been used as an indicator in studies of patients receiving heparin drip therapy, and time in therapeutic range is used for PT/INR studies as a surrogate marker for adverse event rates.

What is for this Coag. testing organized Qualty management s e.g. internal quality control and external quality assessment (PT)?
SEKK, Nymburk, Czech Republic

Marcia L. Zucker, Ph.D.:Most manufacturers have electronic quality control for their instruments which is used to satisfy the CLIA requirement of 2 levels of quality control every 8 hours for coagulation instruments. Each manufacturer also has liquid quality control used to verify the performance of the disposables. There are many external agencies which provide proficiency testing materials for these instruments. It is best to contact the manufacturer of the specific test in use for the list of available proficiency organizations as these vary by instrument and assay for each system.

In testing PT for an neonate of few months old, could I use the control of normal adult person?
port said, Egypt 

Marcia L. Zucker, Ph.D.:The hemostatic system of a neonate is very different from that of an adult, so adult ranges are generally not applicable for this population. In a paper published, some time in the past two years (I don’t have the precise reference handy) by Marilyn Manco-Johnson and Maureen Andrew of Hamilton Hospital where the effects of age on normal ranges were clearly identified.

What are your thoughts on the use of Mean Normal Prothrombin Time and ISI for coagulation near patient testing
Birmigham UK

Marcia L. Zucker, Ph.D.: Both must be used in any PT/INR system. For POC systems, each manufacturer has their own method for incorporating the mean normal PT and the ISI into the INR value reported. In some systems the ISI varies with each lot of reagent, but the appropriate ISI is encoded either on the test strip or in a code chip to account for these fluctuations. Other systems have developed ways to ensure that the ISI does not vary lot to lot, so this becomes a non-issue.

What are the most important interferences for POC?
canada, montreal 

Marcia L. Zucker, Ph.D.:Interferences vary by system, test being performed and sample type. There is no single interference that would apply equally to all possible combinations.

What do you think about the CoaguChek Pro DM from Roche?
Canada 

Marcia L. Zucker, Ph.D.:As I am employed by a manufacturer of POC coagulation instrumentation, I cannot objectively give opinions about the specific systems available.

We have a cardiologist that is moving from the medical group clinic to venture out on his own and he wants to be able to do POC coag testing in his office. What instrument do you recommend for ease of use by nurses in his office doing routine PT and aPTT?
Quincy, Il 

Marcia L. Zucker, Ph.D.:The first consideration for your cardiologist is CLIA licensure. If he is not prepared to obtain a license to perform tests of moderate complexity, he will not be able to perform aPTT assays. If he obtains a CLIA waived license, he can only choose between the ITC ProTime/ ProTime3 system and the Roche CoaguChek/ CoaguChek S to perform PTs. With a moderate complexity license he can choose from any of the systems described in slides 8 through 12 as having both assays.

Our hospital is opening a cardiac unit in Aug 2003 and expects to do open heart surgeries. They want a POC unit that will do ACT, PT, aPTT. What can you recommend to us?
Quincy, Il 

Marcia L. Zucker, Ph.D.:Please review the available systems and their test menus on slides 8 - 12. Each system has its advantages and disadvantages which I am certain their sales representatives would be more than happy to detail for you. You might also ask other open heart centers in your area about their experiences.

It appears that some if not all these testing is headed toward waived testing sometime. I would like to know how by doing any of these coagulation tests incorrectly would not be harmful to the patient. Specifically, if one is to ajusted the dosage of the medication based on these results how can it be considered "minimally harmful"? I'm not sure that many of the users really understand the concept of "monitoring".
Albany, NY 

Marcia L. Zucker, Ph.D.:I disagree with your statement that all these tests are headed for waived status. The two systems currently available as waived systems are the ProTime and CoaguChek/S. The ProTime was reviewed following the 1995 CDC guidelines for waived test classification. Data were submitted to show that the system had sufficient failsafe mechanisms in place to minimize the likelihood of an erroneous result. It is the ONLY coagulation system that has successfully completed this review process, although it is by no means the only system for which an application was made. The CoaguChek received waived status after it was cleared for use at home by patient self-testers. It is critically important to understand that these test results are not intended to be used in the absence of any other information. In many of the inserts for POC coagulation you will find a statement that if the result is in conflict with the patient’s clinical condition, it should be repeated. This is true of any laboratory test. Yes, inaccurate results may be reported with some specific frequency – whether these results are from a conventional laboratory or a POC system, the tests should be repeated if the result is suspect. The advantage in POC is that the patient is right there, and repeating the test is easily accomplished.

Could you please describe your experiences with POCT testing for aPTT and Protimes at the bedside in a tertiary care facility? How are the tests used, ie what kinds of applications? What kind of guidelines should be in place regarding when it is more appropriate to perform laboratory testing rather than POCT testing? At your facility, where does the revenue for this type of testing go? and finally, if at your facility POCT for PT and aPTT is used routinely, what kind of impact, cost wise for the facility and volume wise for the coag laboratory did the implemenation of POCT coag testing have?
Springfield, Massachusetts

Marcia L. Zucker, Ph.D.: The simplest answer to the question of when POC is appropriate for inpatients is to examine the clinical impact turn around time has on patient treatment. For aPTT, this impact is most clearly seen for patients on a heparin drip and for determining when to remove the femoral sheath after catheterization procedures. In either situation, the goal is a very careful titration of the amount of heparin anticoagulant activity present in the patient’s blood. On average, heparin has a half-life of close to 90 minutes, however, this can vary more than 4-fold between individual patients. If it takes an hour or two from the time of sample draw to getting the lab result, the result obtained has no clear relationship to the anticoagulant levels in the patient at the time the result is received. Using POC aPTT (or ACT) the result is obtained in minutes allowing an accurate snapshot of the “current” state of anticoagulation. On the other hand, if aPTT and PT are being ordered on a daily basis as part of the patient’s routine care, it likely does not matter when the result is posted and using the standard laboratory is most likely going to be more cost effective. POC PT seems to have its home primarily in the outpatient anticoagulation clinics, as the effects of warfarin are not immediate, as for heparin, and the benefits of immediate turn around are not as crucial for inpatients. Both guidelines for use and the cost/ revenue stream vary by individual institution. Each site must determine when POC is appropriate for their patient population and write that into their treatment protocols. Some hospital systems have the lab purchase the supplies and bill for the tests, while others have each department purchasing and charging independently. There are as many methods for dealing with this as there are institutions using these tests. You need to determine the appropriate system for your institution.

Could we get a clearer copy of the "complex" drawings of the coagulation pathways or the article that it comes from?
St. Geoge Utah

Marcia L. Zucker, Ph.D.:I got this particular picture from Enzyme Research Laboratories, Inc. It can be viewed at their website - www.enzymeresearch.com - simply click on the coagulation link in the first paragraph on the homepage.

1. We would like to have one ACT method at our institution. Of available FDA approved POC coagulation analyzers, which one(s) will handle ACT testing for cardiac surgery, interventional cardiology, dialysis, ECMO, and critical care patients in a pediatric setting? 2. Slide 62 states "linearity and/or cal/ver not required for coag". Yet on the CAP POCT checklist (last rev. 9/4/01), there are standards regarding linearity and cal/ver: std POC.05350 asks "Is verification of the AMR(analytical measuring range) performed with matrix-appropriate materials of known analyte value appropriate to the AMR of the method system, and is the process documented?", std POC05360 "Are criteria established for verifying the analytical measurement range (AMR) and is compliance documented"? How do you suggest these be fulfilled regarding ACT testing, eg: for Hemochron instrumentation? Along the same lines, any recommendations on how to check instruments 2X per year for correlation of patient results using fresh human samples?
Seattle WA 

Marcia L. Zucker, Ph.D.: In choosing the appropriate ACT, you need to look at the target times used in each clinical application. For cardiac surgery, target times range from >400 to >600, depending on the ACT in use and the perfusionists and anesthesiologists at your institution. Interventional cardiology targets can be as low as 200 – 300, in the presence of platelet inhibitors, to >300 (sometimes 350) for stent placement without platelet inhibitors. Dialysis, ECMO and critical care all require much lower target times, usually 180 – 200 for dialysis and ECMO and anywhere from <150 to <240 for sheath pulls in critical care. To get a single system which can handle all of these, you will want both low and high range ACTs. The Hemochron test tube systems and the Medtronics HemoTec ACTII have classically filled this requirement, but both require larger sample sizes than the newer systems. The Hemochron Jr Signature/ Signature+ system can also perform both low and high range ACTs. The Roche CoaguChek Pro/ Pro DM system ACT cannot go beyond 500 seconds and may not be acceptable in surgery. The Bayer RapidPoint HMT is a high range ACT, but they are supposed to be launching a low range ACT next year. The I-STAT ACT is not cleared for low range applications at this time. The Helena system has the assays available, but still uses larger volumes than might be desired with pediatric populations. I addressed the linearity question and how to compare instruments in earlier responses. As to AMR, in August of this year, I e-mailed CAP to ask about this issue. The reply I received from Linda Palicki stated “at a recent committee meeting the Point of Care Testing Committee members recommended that there be a note added to the questions regarding CRR and AMR in the Point of Care Testing Checklist stating that these do not apply to coagulation testing which reports results in seconds. This suggestion will be sent to the Commission on Laboratory Accreditation for their approval. If approved this note will appear in the appropriate sections of Checklist 30.”

As a recommended peripheral for Home Care expand on YOUR future involvement and what are YOUR recommendations for the clinical laboratory to ensure total errors are kept as close as possible to the laboratory gold standard for coagulation testing.
Seattle Washington

Marcia L. Zucker, Ph.D.:Minimizing total error in a diagnostic assay must be a primary concern of everyone involved. Each manufacturer tries to build accuracy into their system to minimize analytical errors, in one case, the ProTime system, going so far as to allow the option of triplicate testing for each sample. A large component of error for coagulation testing, however, is derived from preanalytical sources, including sample collection, mixing, transports delays, etc. POC systems try to minimize this component by using fresh whole blood. This requires training, of course, of the operators, as to the appropriate methods of fingerstick sample collection. Integral controls can be used to ensure that any gross mishandling of the disposable or the sample will result in errors, rather than erroneous results and clinical judgment, as always, must be exercised in evaluating the answers obtained.

Slide 21 - Why do clinicians ignore recognized differences in ACT methods? How do they determine the Target range for their ACT method? Slide 27 - What is ACT+? And why is it unsffected by Aprotonin? Slide 37/38 - When removing a femoral sheath, how are the target ranges for ACT and aPTT determined at each facility? Slide 41 - What do you mean that POC and lab tests will correlate, but the values won't match, and therapeutic ranges might change? Does this suggest a linear correlation all the time? The slides showing 3 lab instruments using 2 different aPTT reagents doesn't show a picture of linear agreement? Why do different reagents make so much differnce? Slide 42 - Why is the acceptable level of correlation so much lower for coagulation testing? r=0.88 seems to indicate a lot of scatter
Vancouver, British Columbia, Canada 

Marcia L. Zucker, Ph.D.:ACT differences have been ignored in the same way that traditionally, clinicians, through a lack of understanding, have ignored lab to lab differences in coagulation test results. Many clinicians are trained to use a test result without a clear understanding of what is being testing. In the case of chemistries, where you are measuring a single analyte, this is acceptable, as the laboratory will ensure the accuracy and precision of the test that is being used. There is a “true” answer, for example, the concentration of glucose in a sample, and the system can be tested against this true value. In coagulation, you are evaluating the interaction of more than a dozen proteins with various cofactors. Although physiologically, these reactions occur on the surface of a cell (usually a platelet), in the laboratory we remove all the cells before analyzing the sample. There is no “true” value for an aPTT or an ACT, only a comparison to either the heparin level for aPTT or the original Hattersley ACT. The “true” PT/INR is by definition the value obtained using a manual tilt-tube method and the WHO reference thromboplastin. What we substitute for this in our local comparisons is the value obtained by our local lab using the correction factors (ISI and local mean normal PT) for that system. In all these cases, the variables involved are too numerous to count and do not allow the precision we see with chemistry tests. Early POC coagulation references state that “good correlation” was seen with correlation coefficients (r) as low as 0.55. The value of 0.88 has become the de facto standard for comparison over time. The setting of target ACTs also varies by site and system. The historic targets for most applications were set, usually based on one or two papers, using either the manual ACT or the Hemochron tube system. These were the only ACTs available for many years. As newer ACTs were introduced, unless the manufacturer recommended a change in target times, clinicians simply adopted those already in use, whether or not they were applicable to the ACT being used. To my knowledge, only the Hemochron Jr ACT+ assay was ever introduced with the clear statement that target times should be changed to maintain clinical practice when switching to this assay. The ACT+ was developed as a combination reagent for the express purpose of being used in cardiac surgery without being affected by aprotinin, hypothermia and hemodilution. The strength of the activation using this reagent leads to ACT clotting times that are 10 – 15% lower than the standard Celite® ACT tube. Adjusted target times are developed either through clinical correlation between current and new systems or due to the strong preference of the clinicians involved in patient care. Very few outcome studies have been performed to determine with certainty the optimal target times for each ACT system in each clinical setting.

How I can correlate my ITC with my MLA 1400? What will be the minimum value for the Correlation Coefficient within a POCT instrument vs a main plasma reference instrument?
DELRAY BEACH, FL 

Marcia L. Zucker, Ph.D.:There are many different correlation protocols which can be used. ITC’s recommended protocols are posted on the website (www.itcmed.com). Go to products, hospital POC coagulation, then downloads (on the left side of the screen). Scrolling down with take you to various protocols including those for correlation in .pdf format. In general, a correlation coefficient of r = 0.88 (not r2) is considered acceptable for POC coagulation.

Are there any devices that can be used for home monitoring of PT and/or APTT?
Washington, Pennsylvania

Marcia L. Zucker, Ph.D.:There are no aPTT devices for home monitoring. The ProTime, ProTime3 and CoaguChek devices have been FDA cleared for home monitoring of PT.

Since heparin is no longer the only drug on board when an ACT is performed, which method currently available shows the least interference when drugs such as IIb IIIa are used?
Hollywood, FL

Marcia L. Zucker, Ph.D.:Rather than seeking the method with the “least interference” a better question is simply how to manage patients receiving novel therapeutic agents. The difference being that an effect of a novel agent on the ACT may not necessarily be interference, it could give valuable information. For the GPIIb/IIIa inhibitors, the best example is ReoPro. In the EPIC trial, both the Hemochron and HemoTec ACTs were used for monitoring patients. Eli Lilly (the manufacturer of ReoPro) published a statement stating that both systems were elevated in the presence of ReoPro. During the EPILOG trial, the ACT in use was standardized to the Hemochron Celite ACT as that system was already in use by most of the study sites. This study led to the current recommendations, in the ReoPro package insert, for low dose heparin and target ACTs between 200 and 300 seconds. With this in mind, clinicians must decide exactly where to target the ACT they are currently using. I have always recommended, when evaluating any new ACT, that correlation studies include patient samples under all the various drug/procedure combinations possible so that these issues are addressed before a decision is made to change systems.

I sent this yesterday, not sure if it went through: We use Roche Coaguchek and require 10% correlation of fingerstick samples with lab testing. Do we usually have around 60 correlations per month. ALl lower INR's are always right on, but there are always 3-6 INR's per month that don't correlate good. Their difference would mean a difference in treatment. Oct 2002 bad ones were f3.2/L2.5, f>4/L2.7, f3.8/L2.8. Our upper cutoff is >4 for lab confirmation. What is it about the POC testing that there are ALWAYS these same few each month that are bad? It does not appear to be technique, operator, instrument, strip, instrument, bili, or hgb related. It seems it is always the fingerstick one is higher, the lab one lower. Is there some interference with the patients blood /drugs/chemistries...and the iron particles on the strip?
Pittsburgh, PA

Marcia L. Zucker, Ph.D.:I cannot answer specifically as to the factors that will affect the CoaguChek – you would have to check with Roche for that, in general however, there are many conditions that could, theoretically affect the fingerstick INR and not the lab. You touched on some – the patient’s drugs and chemistries are likely candidate. An extreme example of this would be a patient with undiagnosed Lupus or antiphospholipid antibodies; these affect each PT reagent differently. Some discrepancies are to be expected, even if you compare two different laboratory systems. Having a clear value above which confirmatory testing is done is important. It is also important to evaluate each result in light of the patient’s history. If an INR of >4 is seen on a patient who is tested every two weeks and has been stable for months, a repeat test should be performed. Clinical staff should always look for reasons for unexpected results, whether due to changes in patient lifestyle or meds or due to an error in the test.

I would like to know Dr. Zucker's ideas on the Thromboelastograph. This seems to give a complete coagulation picture, better than other testing.
Phoenix, Arizona

Marcia L. Zucker, Ph.D.:Personally, I think the TEG has a lot of value, but I do not think that it replaces the more common tests. In the past, the TEG was difficult to use and interpret and tests took a long time. I am told that this has changed with the new version of the instrument, but I do not have direct experience with this. Used as an adjunct by someone properly trained in use and clinical interpretation, I think it gives excellent information and a more detailed analysis of the various components of coagulation.

Does most clients use the data management from the Hemochron Signature, Jr. for Q.A.? Or do use a manual log sheet for documentation purposes (i.e. results, temperatures,daily Q.A.)?
Seneca, S.C. 

Marcia L. Zucker, Ph.D.:There is no single procedure used by "most" sites. System specific downloads and data management, vendor neutral systems and paper logs are all still used routinely in many clinical facilities. The choice must be made by each site.

With the high-end differences you show between Innovin and TPC INR values, do you think the labs should restrict their reportable ranges?
Indianapolis, IN

Marcia L. Zucker, Ph.D.:These data are not shown to limit the reportable range for these laboratory reagents, but to bring to everyone’s attention that the discrepancies seen between POC and lab are not necessarily because POC is less accurate. The INR system is not perfect. A clotting time (PT) is converted to an INR through a ratio (Patient PT/Mean normal PT) which is raised to the power of the ISI. The mathematics involved ensures that any small differences at the low end will become significantly larger as the values increase – it’s an exponential equation. The critical point to understand is that this variability does exist and should be considered when treating patients.

What is the acceptable limits between two methodologies for INR?
Bronx,NY

Marcia L. Zucker, Ph.D.:It depends on whom you ask. In general, it seems accepted that differences of +/- 0.4 INR should be expected. There are publications looking at these differences between laboratories that suggest differences of up to 0.7 are also acceptable. The other consideration is what values you are comparing. For a patient being maintained in a therapeutic range of 2.0 – 3.0, there is no difference between 2.1 and 2.9, but a clear difference between 2.7 and 3.5 although both these comparisons differ by 0.8 INR.

What is the precision requirement for a whole blood based coagulation test? is 10% acceptable?
Minneapolis, MN

Marcia L. Zucker, Ph.D.:The 10% precision value seems to be the accepted standard for the industry. Experienced operators using whole blood samples can frequently obtain better precision. When precision is analyzed using control preparations, using either lyophilized plasma or whole blood samples, the test substrate itself will increase the variability due to rehydration/ recalcification issues. Some sites with whom I have spoken feel that 10% for whole blood and 14% for control samples is acceptable.

I am concerned about regulating treatment for patients who have their PT/INR testing performed at different laboratories using different testing methods. Isn't there a clinical significance between capillary (POC)PT/INR and venous (lab) PT/INR? Would you recommend coagulation clinic patients routinely have their PT/INRs performed using the same method? Hasn't there also been studies that have shown a clinical significance in POC PT/INRs between different operators who use the same method?
Phoenix, AZ

Marcia L. Zucker, Ph.D.: Your concern is well founded, but not because of clinical differences between capillary and venous tests. The differences observed between these types of systems is no worse than that seen between geographically distinct laboratories, sometimes just across the street. It is important that a patient’s treatment be guided by a single test system for INR as much as possible. Many papers have been published which stress this as the primary consideration – using multiple laboratories often leads to frequent dose changes. This in turn leads to less time in therapeutic range because of the continual adjustment to the INR.

We are using the ProTime coagulation instrument for PT testing in our Nursing Homes. The INR in the instrument is based on a mean normal of 13.1 by the manufacturer but the mean normal of our population is 10.7. The mean normal can not be changed in the instrument. How will this affect the comparison of INR between these POC instruments and the INR from the main laboratory?
Norfolk, VA

Marcia L. Zucker, Ph.D.: The answer to your question will depend on where the mean normal of 10.7 was determined. The ProTime mean normal of 13.1 was generated from a very large geographically diverse population using the reagent in the ProTime cuvettes, which has an ISI of 1. A mean normal value of 10.7 sounds as though it was determined on a laboratory system with a less sensitive reagent, likely an ISI of near 2. The INR system was designed to correct for these large differences in PT seconds, and although it is not perfect (as I described earlier) it is much better than comparing the PT seconds. The only way to clearly answer your question would be for you to run a correlation study of the ProTime to your local laboratory.

That wraps up this session of Expert Access Live Online. Thanks to everyone who posted a question for this month’s expert, and thanks also to our expert, Dr. Marcia Zucker. We hope you found today’s presentation and Q&A segment to be informative and useful. This Expert Access session, and all previous sessions, are archived on our website in order to serve as a continuing source of education.

AACC would like to again thank the Bayer Corporation for making this educational program possible.