Can someone explain to me what the INR TEST is

tridil2000, MSN, RN · Jul 19, 2005

I am trying to finish up an assignment and I know what the INR test is, but what do low values Indicate and what to high values indicate.
Isn't this test the same as the PT but more thourough?
What is the expected Norm?
What is the Treatment plan?
Anyone???

try this link:

http://www.api-pt.com/pdfs/2002Binr.pdf

i think it's a good explanation. if you're still lost just say so! :specs:

Editorial Team / Admin · Jul 19, 2005

i am trying to finish up an assignment and i know what the inr test is, but what do low values indicate and what to high values indicate.
isn't this test the same as the pt but more thourough?
what is the expected norm?
what is the treatment plan?
anyone???

o.k., you know that inr=international normalized ratio

this is included in a pt (protime). now known as pt/inr. ( pt was necessary to determine the efficacy of anticoagulation treatment). labs measuring the pt would get variable readings within their own facility and, because so many labs had norms, lows, highs different from each other, a standard had to be set, hence, the inr. the pt will be different in most all labs, but, the inr will usually be read out the same in all labs.

low values would indicate usually the individual was not on coumadin (warfarin) or not on enough to be in the range needed for treatment.

high values would normally indicate high therapeutic range and/or abnormally high.

since the inr is internationally used, (a value of 2.0-3.0 is used to manage dvt prophylaxis, some atrial fibs and prevention of continued clotting in mi's, 2.5-4.0 is a range used to manage prosthetic heart valves) patients traveling could now use their weeks previous value to compare to a value obtained states or countries away.

it must be noted, however, that the proper calibration of equipment and use of a practical sensitized solution is mandatory for this to be truly recognized as a no fault system with little or no variability. a universal standardized sensitive reagent has to be developed for this to happen.

siri, crnp, clnc, rlnc

misswoosie · Sep 25, 2005

o.k., you know that inr=international normalized ratio
this is included in a pt (protime). now known as pt/inr. ( pt was necessary to determine the efficacy of anticoagulation treatment). labs measuring the pt would get variable readings within their own facility and, because so many labs had norms, lows, highs different from each other, a standard had to be set, hence, the inr. the pt will be different in most all labs, but, the inr will usually be read out the same in all labs.
low values would indicate usually the individual was not on coumadin (warfarin) or not on enough to be in the range needed for treatment.
high values would normally indicate high therapeutic range and/or abnormally high.
since the inr is internationally used, (a value of 2.0-3.0 is used to manage dvt prophylaxis, some atrial fibs and prevention of continued clotting in mi's, 2.5-4.0 is a range used to manage prosthetic heart valves) patients traveling could now use their weeks previous value to compare to a value obtained states or countries away.
it must be noted, however, that the proper calibration of equipment and use of a practical sensitized solution is mandatory for this to be truly recognized as a no fault system with little or no variability. a universal standardized sensitive reagent has to be developed for this to happen.
siri, crnp, clnc, rlnc

i would also like to add thatinr is used specifically to measure the anticoagulant effect of warfarin only and should not be requested as part of a clotting screen.similarly there is no point in doing a clotting screen on someone on warfarin as it would obviously be deranged.the inr has no units attached to it and is merely a ratio.also it is fairly unusual to use warfarin to an inr of 2-3 for dvt prophylaxis-more usually use lmwh.also very uncommon to have target inr ranges of greater than 4 even with mechanical valves because of the bleeding risk.maj of pts req anticoag eg afs for stroke prevention and treatment of pe/dvt are 2-3 range

mwbeah · Sep 25, 2005

international normalized ratio (inr)

more than 2 million americans are estimated to be treated with warfarin (national center for statistics, 1984). as with any medical treatment the weighing of risks and benefits must be carefully balanced. anticoagulation agents have a narrow therapeutic index, and the more narrow the therapeutic index, the greater the chance for adverse effects, i.e., bleeding (ortel, 1995). to achieve optimal effects and evaluate the patient's response to warfarin, the clinician must keep in mind several important concepts. first, the intensity and duration of the therapy depends on the identified need for treatment. second, the dose of warfarin must be patient specific, and lastly, periodic assessment of effectiveness is necessary due to warfarin's narrow therapeutic index. considering the aforementioned facts, the blood test chosen to monitor the patient's response to warfarin must be accurate, reliable and cost effective (ortel, 1995). the traditional method of determining the efficacy of anticoagulation therapy is the prothrombin time (pt). this was first described by armand j. quick in 1935. he used thromboplastin derived from rabbit brains to prove his assumption that patients with bleeding abnormalities secondary to obstructive jaundice was due to a deficiency of prothrombin. this is now know to result from reduced levels of liver-produced vitamin k-dependent blood coagulation factors ii, ix, and x (florell & rodgers, 1996).

today a blood sample is collected in a tube containing citrated sodium, in the laboratory the sample is spun in a centrifuge, and a specific volume of thromboplastin reagent is added to the sample. the time until a fibrin clot forms, measured in seconds, is reported as the pt (ortel, 1995). the thromboplastin reagent can be either an extract of mammalian tissue (lungs heart or brain of animals) rich in tissue factor, or a recombinant proportion of human tissue factor in combination with phospholipids (hirsh & poller, 1994).

because thromboplastins are produced using different methods and from different sources, the sensitivity of an individual thromboplastin to another can vary greatly. the more sensitive the thromboplastin reagent the longer the resulting pt. conversely, the less sensitive the reagent the shorter the resulting pt. variance can even occur within a single batch depending on shelf time (ortel, 1995). this variability in sensitivity and its effect on pt outcomes can have a major detrimental effects on the management of warfarin therapy in patients requiring anticoagulation. this variability has also caused great international debate and concern for several decades (florell & rodgers, 1996).

to help standardize this difference two formats were developed, the first was the international sensitivity index (isi) and the second was the international normalized ratio (inr). the inr was developed to incorporate the isi values and attempt to make pt results uniformly useable. the manufacturers assign an isi to each batch of reagent after comparing each batch to a "working reference" reagent preparation. this "working reference" has been calibrated against internationally accepted standard reference preparations which have an isi value of 1.0 (ortel, 1995). by definition, the more sensitive thromboplastin have an isi of less than 1.0 and the less sensitive are greater than 1.0. the isi value is critical for calculation of the inr, because the isi value is the exponent in the formula. consequently, small errors in the isi assignment may affect the calculated inr substantially (florell & rodgers, 1996).

to resolve the problem of highly variable pts, the use of the inr has been recommended for monitoring patient's oral anticoagulant therapy. this recommendation is supported by the american college of chest physicians, the national heart, lung and blood institute and the british society for hematology (nichols & bowie, 1993).

it is important to emphasize that the inr is not a new laboratory test. it is simply a mathematical calculation that corrects for the variability in pt results attributable to the variable sensitivities (isi) of the thromboplastin agents used by laboratories.

inr = - patient pt______ isi

or

inr = {ptr}isi

mean normal pt

ptr- is the prothrombin time ratio, which is the patient's observed pt (in seconds) divided by each laboratory's calculated mean normal pt (in seconds) (ortel, 1995, florell & rodgers, 1996).

a target inr range of 2.0 to 3.0 is recommended for most indications, such as treatment or prophylaxis of dvt, prevention of further clotting in mi's and other preventive measures for patients with atrial fibrillation. an inr of 2.5 to 3.5 is recommended for patients with prosthetic heart valves (ortel, 1995).

using the inr in other medical conditions, such as coagulopathy or liver disease has not been deemed appropriate as of this time, because inr was originally developed using anticoagulated patient populations. despite its usefulness during routine monitoring of warfarin therapy, the use of inr for monitoring during the induction phase of therapy has not been fully supported (hirsh & poller, 1994). reliability is lost during the initial days of therapy because of the varying rates of plasma clearance of vitamin k-dependent clotting factors. these factors are what the thromboplastin reagents are sensitive to and in turn what the inr and ptr are actually reporting. in addition, individual thromboplastin reagents vary in their sensitivities to the vitamin k-dependent clotting factors (ortel, 1995).

the inr system can be precise and valid when a sensitive thromboplastin and manual method of clot detection are used. however, it loses precision and accuracy when used to convert pt ratios obtained with less-sensitive thromboplastin reagents or when automated clot detection systems are used. these problems can be avoided by using reagents with low isi's and proper calibration of machinery.

although the inr system is far from perfect, it is the only practical solution currently available. with all of its faults, it is much better than an unadjusted pt system. although the clinician would like a system with little or no variability, the goal is unattainable unless a standardized sensitive reagent is universally adopted.

references:

florell, s.r. & rodgers, g.m. (december,1996). the pt and the pendulum. american journal of clinical pathology, 699-700.

hirsh, j. & poller, l. (1994). international normalized ratio: a guide to understanding and correcting its problems. archives of internal medicine, 154, 282-288.

national center for health statistics, cypress, b.k. (september, 1984). patterns of ambulatory care in internal medicine. the national ambulatory care survey, united states, january 1980-december 1981. vital and health statistics, series 13, no. 80. dhhs pub. no. (phs) 84-1741. public health service. washington d.c.: u.s. government printing office.

nichols, w. l. & bowie, e. j. w. (1993). standardization of the prothrombin time for monitoring orally administered anticoagulant therapy with use of the international normalized ration system. mayo clinical procedure, 68, 897-898.

ortel, l.b. (1995). international normalized ratio (inr); an improved way to monitor oral anticoagulant therapy. nurse practitioner

bluesky, BSN, RN · Sep 25, 2005

I would also like to add thatINR is used specifically to measure the anticoagulant effect of warfarin only and should not be requested as part of a clotting screen.Similarly there is no point in doing a clotting screen on someone on warfarin as it would obviously be deranged.The INR has no units attached to it and is merely a ratio.Also it is fairly unusual to use warfarin to an INR of 2-3 for DVT prophylaxis-more usually use LMWH.aLSO VERY UNCOMMON TO HAVE TARGET INR RANGES OF GREATER THAN 4 even with mechanical valves because of the bleeding risk.Maj of pts req anticoag eg AFs for stroke prevention and treatment of PE/DVT are 2-3 range

This is my experience as well.

ICRN2008, BSN, RN · Sep 26, 2005

Because thromboplastins are produced using different methods and from different sources, the sensitivity of an individual thromboplastin to another can vary greatly. The more sensitive the thromboplastin reagent the longer the resulting PT. Conversely, the less sensitive the reagent the shorter the resulting PT. Variance can even occur within a single batch depending on shelf time (Ortel, 1995). This variability in sensitivity and its effect on PT outcomes can have a major detrimental effects on the management of warfarin therapy in patients requiring anticoagulation. This variability has also caused great international debate and concern for several decades (Florell & Rodgers, 1996).

To help standardize this difference two formats were developed, the first was the International Sensitivity Index (ISI) and the second was the International Normalized Ratio (INR). The INR was developed to incorporate the ISI values and attempt to make PT results uniformly useable. The manufacturers assign an ISI to each batch of reagent after comparing each batch to a "working reference" reagent preparation. This "working reference" has been calibrated against internationally accepted standard reference preparations which have an ISI value of 1.0 (Ortel, 1995). By definition, the more sensitive thromboplastin have an ISI of less than 1.0 and the less sensitive are greater than 1.0. The ISI value is critical for calculation of the INR, because the ISI value is the exponent in the formula. Consequently, small errors in the ISI assignment may affect the calculated INR substantially (Florell & Rodgers, 1996).

This is an excellent explaination of why laboratories now report out the INR instead of the PT. This is especially important if a patient is having their Coumadin therapy monitored by more than one laboratory or if the laboratory changes to a new lot of reagent. Thank you for sharing!

GingerSue · Sep 26, 2005

wrong thread that I entered