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 Table of Contents  
Year : 2019  |  Volume : 16  |  Issue : 2  |  Page : 98-102

Point-of-care monitoring of international normalized ratio among patients with mechanical valves in Jos, North-Central, Nigeria

1 Department of Paediatrics, University Teaching Hospital, Jos, Plateau State, Nigeria
2 Department of Paediatrics, University of Minnesota and HCMC, Minnesota, USA

Date of Submission04-Dec-2017
Date of Decision21-Sep-2018
Date of Acceptance28-Nov-2018
Date of Web Publication11-Nov-2019

Correspondence Address:
Dr. Ishaya Ibrahim Abok
Department of Pediatrics, Jos University Teaching Hospital, PMB 2076, Jos, Plateau State
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njc.njc_39_17

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Background: Rheumatic heart disease is the leading cause of acquired valvular heart disease in low- and middle-income countries and sometimes requires mechanical valve replacement. Postsurgical management of these patients is vital and includes lifelong anticoagulation with close monitoring.
This study aims to report our experience with anticoagulation monitoring of patients with mechanical heart valves using a handheld portable device.
Patients and Methods: This retrospective review involved 12 patients that were enrolled in the anticoagulation clinic (AC) of a local nongovernmental organization, at different times between 2003 and 2012. Patients' sociodemographic variables, international normalized ratio (INR) assay results, and clinical status were routinely entered into a register and were retrieved for the present review.
Results: The 12 patients comprised three males and nine females and were resident between 3.7 and 300 km from the AC. Their age ranged from 7 to 26 years (mean 14.1 ± 3.3 years, median 13 years) at the time of enrollment into the AC. Seven hundred and ninety-four INR assays were done during the period under review (mean 12.2 ± 5.4 INR assays per patient per year). Of the 794 assays, 38.5% were within target (INR levels between 2.5 and 3.5 or between 2.0 and 3.0 for patients with mechanical valves at the mitral and aortic positions, respectively) 35.7% were below the target range, and 25.7% were above the target range.
Conclusion: Our experience with point-of-care INR testing in a clinic setting suggests that adopting this approach could improve the quality of anticoagulation monitoring by increasing patients' access to the device, the frequency of assays per patient, and, ultimately, the number of within-target INR assays.

Keywords: International normalized ratio, mechanical, valve

How to cite this article:
Abok II, Andeyaba B, Slusher T, Bode-Thomas F. Point-of-care monitoring of international normalized ratio among patients with mechanical valves in Jos, North-Central, Nigeria. Nig J Cardiol 2019;16:98-102

How to cite this URL:
Abok II, Andeyaba B, Slusher T, Bode-Thomas F. Point-of-care monitoring of international normalized ratio among patients with mechanical valves in Jos, North-Central, Nigeria. Nig J Cardiol [serial online] 2019 [cited 2023 Mar 26];16:98-102. Available from: https://www.nigjcardiol.org/text.asp?2019/16/2/98/270689

  Introduction Top

Sub-Saharan Africa has been identified as the world's hotspot of rheumatic fever and rheumatic heart disease (RHD), with schoolaged children, adolescents, and young adults being predominantly affected.[1],[2] The majority of these patients present late with damaged heart valves that often require valve replacement surgeries.[3] The cost and availability of cardiac surgery are the major obstacles to the care of such patients with valvular heart damage.[4] If these obstacles are overcome and prosthetic mechanical heart valves are implanted, these patients require lifelong anticoagulation therapy to prevent mechanical valve occlusion via thrombus formation. Oral warfarin remains the most frequently used drug for this purpose, especially in developing countries.[5],[6],[7]

In order to achieve the desired level of anticoagulation and prevent thrombosis or hemorrhage that may arise from under- or over-coagulation, it is necessary to frequently monitor the international normalized ratio (INR) which is a global standardized measure of pro-thrombin time, a concept first proposed by the World Health Organization in the 1980s.[8],[9] The target value of INR acceptable for patients with mechanical valves differs with centers and protocols,[5] but generally a target value of 2 and a range of 2.0–3.0 are acceptable for the low thrombotic risk group but who are at higher risk of hemorrhage (such as those with aortic metallic valves, in sinus rhythm), while a target value of 3 and a range of 2.5–3.5 are acceptable for patients with mitral prosthetic valves.[6] Thus, INR monitoring is an essential part of optimal management of patients with mechanical heart valves.[5],[6]

Due to the technicalities involved, INR assay in low-income settings may only be available in tertiary, regional, or specialist hospitals, which are often located in urban areas. With RHD being a disease of the rural and urban poor, the patients often may not have easy access to such hospital facilities. Moreover, multiple hospital visits (e.g., for test ordering, bleeding, and collection of results) may be required to obtain a single INR result from the hospital laboratory, with additional health-care costs that may contribute to poor compliance and loss to follow-up. These factors affect the modalities and feasibility of INR monitoring and control, with the problem heightened significantly for those who live in rural areas.[3]

Handheld portable devices have been shown to be reliable and effective in other parts of the world. Point-of-care (POC) devices are applied in basic tests such as glucose assay and complex test that assess coagulation. A POC test enables the physician or health-care worker to carry out laboratory test near the patient, thereby achieving its aim of accelerating diagnosis and therapeutic interventions, especially in emergency and critical care points. It is now a major tool in the practice of ambulatory medicine and home-care health service. This has resulted in improved patient outcome and reduction in health-care costs.[10],[11],[12],[13]

We report our initial experience with INR monitoring of a small population of children and young adults with prosthetic valves using such a portable device in a clinic setting.

  Patients and Methods Top

A portable INR monitoring device (Coaguchek®, Roche, USA) was donated in 2003 to Heart Aid Trust, Inc., a Nigerian nongovernmental organization (NGO). It was donated to support the care of a child with severe rheumatic mitral valve disease who received a prosthetic mechanical mitral valve. The NGO elected to domicile the device in the outpatient clinic of the NGO in order to allow other indigent patients requiring the service to benefit from it at no cost to their families. The clinic staff were trained on the use of the portable device based on the manufacturer's manual. The patients and their families were educated on the need for, and implications of, long-term treatment with warfarin, including the necessity of drug compliance and regular monitoring of INR levels. They were also instructed to report any illnesses or bleeding episodes.

At each visit, a small sample of capillary whole blood obtained via a finger puncture was placed on a test strip which was inserted into the portable Coaguchek® (Roche, USA) apparatus. The INR and prothrombin time (PT) results were displayed on the device screen within 90 s.

The frequency of INR monitoring varied from weekly to four weekly, depending on the need for warfarin dose adjustments, with the aim of maintaining the INR levels between 2.5 and 3.5 or between 2.0 and 3.0 for patients with mechanical valves at the mitral and aortic positions, respectively. The device was in use from mid-2003 until mid-2012, when a newer model of the device was introduced into the market and the test strips for the older model were no longer available. Data routinely collected during the period (INR and PT values, warfarin dosage adjustments with dates, sociodemographics, indication for valve replacement, and vital status at mid-2012) were retrospectively analyzed to provide an overview/profile of INR assay results and warfarin usage during the period of use of the equipment.

Data were processed and analyzed using Epi-Info version 7 (CDC, Atlanta, Georgia, USA). INR values within the above-stated ranges were defined as adequate control. The mean, median, and range of continuous variable were determined, whereas frequency tables were generated for categorical variables.

  Results Top


Twelve patients received regular INR monitoring during the period under review, comprising three males and nine females, and their age ranged from 7 to 26 years (mean age was 14.1 ± 3.3 and median age was 13 years) at the time they registered for the service. Using the Olusanya[14] classification, none of the patients were in the upper socioeconomic class (SEC) and 41.65% and 41.65% were in the middle and lower SEC, respectively, whereas complete data on SEC were not available for two (16.7%) patients. Travel time to the clinic ranged from 6 to 180 min (median 46.0 min) [Table 1].
Table 1: Sociodemographic and clinical profiles of the patients

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Clinical status

Seven of the 12 patients (58.3%) had their prosthetic valves at the mitral position, three (25%) at the aortic position, while two (16.7%) patients had both aortic and mitral prosthetic valves.

International normalized ratio

The duration of follow-up per patient ranged from 6 to 102 months, with mean and median values of 40.6 ± 32.5 and 45.5 months, respectively. The total duration of follow-up was 57 patient-years, with a mean of 4.8 ± 3.0 patient-years.

A total of 794 INR measurements were performed over the review period. The number of assays per patient ranged between 9 and 185 assays, with mean and median values of 66.2 ± 59.6 and 45.5 assays, respectively. The yearly frequency of INR assays is presented on the bar chart in [Figure 1].
Figure 1: Number of international normalized ratio assays per year during the period of review

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The average number of INR assays per patient per year ranged from 5.5 to 24 assays, while the overall mean and median numbers of assays per patient per year were 12.5 ± 5.4 and 3.5 INR assays, respectively.

The INR values obtained ranged between 0.9 and 8.0, with an overall mean INR of 2.8 ± 1.3 and a median value of 2.6. Of the 794 INR assay results, 38.5% were within target range, while 35.7% and 25.8% were below and above the target range, respectively. [Table 1] shows the vital status of each patient at the end of the follow-up period and details of INR measurements, including total number of assays, mean INR during the period, and the number (percentage) of times INR fell outside the target range [Table 2].
Table 2: Individual international normalized ratio of controls and outcome in the study participants

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Clinical events/outcomes

Three mortalities were recorded during the period of follow-up. One patient died from prosthetic mitral valve occlusion despite within-target INR values; the two other mortalities were both out of hospital, one being a sudden event, whereas no information was available concerning the circumstances of the other. None of the other nine patients reported any hemorrhage or thromboembolic events during the period of review.

  Discussion Top

This study reveals, first, that physician-centered management of anticoagulation (usually a hospital/clinic-based approach) can be effectively integrated with POC testing (a self-care approach). This integration may be advantageous especially in resource-poor communities because it removes the barrier that arises from the nonavailability of an efficient laboratory service while reducing the economic burden that may arise from multiple hospital visits.[12] Second, it improves our patients' access to INR testing, by increasing the utilization of the POC device from a single individual to at least 12 patients as observed in this review, with a potential for even more. Third, in addition to the immediate availability of results, POC testing, as observed in this report, provided the managing physician the opportunity to immediately adjust warfarin doses, clinically evaluate the patient, and provide needed counseling and/or education.

In the current report, we performed an overall mean of 12.5 INR assays per patient per year. Ogendo et al.[15] reported six INR assays per patient per year, among Kenyan patients with mechanical valves attending an anticoagulant clinic. A similarly low frequency of assays has been reported elsewhere in Nigeria.[16] The use of a POC device, as in this report, may have a direct influence on the frequency of INR testing. Being much less cumbersome than laboratory testing (which requires multiple visits; one for blood sampling, another for collection of the result, and yet another for review of result by the managing physician), it becomes much easier to increase or decrease the interval between INR assays, depending on the need to adjust warfarin doses in individual patients. By delivering the assay results immediately, POC testing also reduces travel time and costs by at least two-thirds since only one visit is required instead of three.

This report also shows that over 38% of assays were within the disease-specific target limit during the follow-up period, a finding similar to 44.2% reported in India but higher than 12% and 18% reported among South African and Kenyan heart patients, respectively.[15],[17],[18] The high proportion of within-target assays observed in this study might be connected to the close titration associated with the increased frequency of testing using the POC device, which has also been demonstrated in previous studies.[10],[11],[12] The population characteristics might not differ significantly as majority of our patients are within the middle and lower socioeconomic strata, a fact that is common to most RHD patients across the developing world. Although this review demonstrated a higher proportion of within-target INR assays than that of comparable studies in sub-Saharan Africa, the proportion (38%) is still not optimal compared to well-established anticoagulation centers where over 50% of INR assays are within the target limits.[19],[20] In such communities, the introduction of self-monitoring using POC testing has been shown to further improve the within-target INR values to about 80% or greater.

The fact that the assay was made available to indigent patients at no cost may also have contributed to the increased frequency of INR testing observed in our study. This inference can be drawn from the reported link between health service fees in low- and middle-income countries and poorer health access and outcomes.[20]

The availability of appropriate, prompt, livesaving health intervention is a critical determinant of mortality in emergencies.[21] Such emergency cardiac surgical intervention is not available in our locality. Thus, one of our patients who was demonstrated to have mitral valve obstruction despite within-range INR died in the hospital. The valve obstruction in this patient was probably caused by a pannus (these are formed by excessive granulation tissue growth on a mechanical prosthetic valve) rather than a thrombus since the INR control in this patient (AD) was fairly comparable with other patients. It is essential for the clinician to differentiate a pannus from a thrombus because a thrombus of <0.8 cm2 if present can be treated using fibrinolytic agents only, whereas a pannus may require open-heart surgery.[22] Therefore, echocardiography is an important tool for the diagnosis of valve obstruction, but the transthoracic echocardiography (which is what was available to us) is limited in differentiating between a pannus and a thrombotic obstruction.[23] Gunduz et al.[24] were able to differentiate between them with a high sensitivity and a high specificity using 64-slice multidetector computed tomography technology.

It is difficult to determine the causes of death in the other two patients since both died at home. However, the suddenness of one of the deaths in an otherwise stable patient (UD) would suggest an arrhythmia, whereas the other (ML) had earlier demonstrated poor compliance as shown by her INR being below the target range 77.3% of the time, compared with 35.7% for the entire group.

  Conclusion Top

Our experience shows that the integration of POC testing, meant for self-care, within an anticoagulation clinic, in a resource-limited setting, can be novel because it increases access, the frequency of assaying, and, ultimately, the proportion of within-target INR assays. In this report, we have described our experience with the use of a portable POC device meant primarily for self-care, a practice that may be novel in low-resource settings but have shown to improve the outcome of anticoagulant care in other places.[10],[11] This sentence should be part of the conclusion of this discussion and not an opening sentence.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2]

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