Safety relevant knowledge of orally anticoagulated patients without self-monitoring: a baseline survey in primary care
© Chenot et al.; licensee BioMed Central Ltd. 2014
Received: 13 January 2014
Accepted: 20 May 2014
Published: 25 May 2014
Effective and safe management of oral anticoagulant treatment (OAT) requires a high level of patient knowledge and adherence. The aim of this study was to assess patient knowledge about OAT and factors associated with patient knowledge.
This is a baseline survey of a cluster-randomized controlled trial in 22 general practices with an educational intervention for patients or their caregivers. We assessed knowledge about general information on OAT and key facts regarding nutrition, drug-interactions and other safety precautions of 345 patients at baseline.
Participants rated their knowledge about OAT as excellent to good (56%), moderate (36%) or poor (8%). However, there was a discrepancy between self-rated knowledge and evaluated actual knowledge and we observed serious knowledge gaps. Half of the participants (49%) were unaware of dietary recommendations. The majority (80%) did not know which non-prescription analgesic is the safest and 73% indicated they would not inform pharmacists about OAT. Many participants (35-75%) would not recognize important emergency situations. After adjustment in a multivariate analysis, older age and less than 10 years education remained significantly associated with lower overall score, but not with self-rated knowledge.
Patients have relevant knowledge gaps, potentially affecting safe and effective OAT. There is a need to assess patient knowledge and for structured education programs.
Thrombosis and atrial fibrillation are the major indications for oral anticoagulation therapy (OAT). Due to an increase in aging population, the number of adults with atrial fibrillation will increase considerably. Consequently, a global increase in the number of patients requiring OAT is expected over the next decades . The effectiveness of OAT to reduce risk of stroke or recurrent thrombosis has been proven and OAT is recommended in guidelines [2, 3]. Frequently used drugs for OAT are warfarin, phenprocoumon and acenocoumarol. Studies have shown that insufficient adherence and a low level of patient knowledge about OAT are the primary causes for complications [4–6]. OAT thus requires regular monitoring of the international normalized ratio (INR) and dose adjustments, as well as a high level of patient knowledge and adherence to recommendations on nutrition, medication and recognition of critical situations. Bleeding complications occur in 0.3 to 0.4% of all patients with OAT every year, but risk estimates vary widely [7, 8]. While educational programs, self-monitoring and self-management of OAT have been established this is not suitable for many patients . Standardized education programs for patients without self-monitoring are lacking in many countries [4, 6]. The best strategy to educate patients about oral anticoagulation has not been determined yet [10, 11]. In Germany, general practitioners manage the majority of patients with OAT, there are no coagulation clinics. Some general practitioners use self-written patient information brochures to inform patients about OAT. Content and quality of these brochures is heterogeneous and sometimes inaccurate. It is known that information brochures on OAT require reading levels, exceeding the capacity of many patients .
The aim of this study was to assess patients’ knowledge about OAT and factors associated with patient knowledge.
This is a baseline survey within a cluster-randomized controlled study conducted in 22 general practices in Germany. The Ethics Committee of the medical school of the University of Göttingen approved this study. A detailed study protocol has been published .
Recruitment of practices and patients
Demographic data of the participants and patient knowledge about OAT were collected at baseline with a self-developed questionnaire based on models from the literature [14, 15]. We chose to use a self-developed questionnaire, because we felt that existing instruments were not comprehensive enough or were not sufficiently adaptable to the specific situation in Germany. The questionnaire evaluated patient knowledge about general information on OAT, and relevant facts regarding nutrition, drug-interactions and other safety precautions such as recognition of complications and informing health care professionals about OAT. Questions were based mainly on relevant national guidelines and expert knowledge [3, 10, 16]. The questionnaire was piloted previously with 12 patients in a practice, which did not participate in the trial using the think aloud technique  and optimized accordingly to ensure comprehensibility.
An English version of the questionnaire is available online . Participants had to fill out the questionnaire themselves under supervision in the practice, without any assistance. Patient names and other confidential information were coded to make it difficult to track individual patients. Informed consent and questionnaires were returned to the study center separately by the practice.
Categorical data were summarized as frequencies and percentages, quantitative variables as medians and interquartile ranges (IQR). For the 13-item knowledge score, all thirteen questions were weighted equally with one point. The total-sum score ranges from 0 to 13, with higher scores indicating greater knowledge.
For questions with multiple yes/no answers the one point awarded to the question in total was divided across all answers. Correct answers received twice the weight of incorrect answers. Indicating “I don’t know” led to 0 points irrespective of which other correct or incorrect answers were ticked. For instance, in question 12 the first four answers were correct, the fifth answer was incorrect, the sixth was “I don’t know”. The four correct answers were weighted by 2/9 points each. The fifth answer which was incorrect carried a weight of 1/9. “I don’t know” carried no weight. For example ticking the first four answers in question 12 gave the maximum score of 1 point. Ticking the first five answers was awarded 8/9 points. Ticking all six answers resulted in no point at all.
To explore factors associated with the score we conducted univariate and multiple regression analyses fitting linear mixed effects models with age, gender, years of education (dichotomized to “less” and “more or equal” than 10 years), fear of bleeding, history of prior OAT related complications, self-rated knowledge as fixed effects, and practice as random effect. The latter accounted for possible correlations between patients from the same practice and thereby adjusted for possible cluster effects. SAS 9.3 (SAS, Cary, NC) was used for statistical analysis. P-values were not adjusted for multiplicity and p-values smaller than 0.05 are referred to as statistically significant.
Socio-demographic and clinical characteristics (n = 345)
74 years (68–78)
< 10 years education
≥ 10 years education
Indication for oral anticoagulation according to the patient**
Deep vein thrombosis
Artificial heart valve
Unknown to the patient
OAT related complication in history
Self-rated knowledge about OAT
Afraid of complications
Answers to questionnaire assessing knowledge on oral anticoagulation therapy (n = 345)
Correct n (%)
Incorrect* n (%)
Indication for OAT known
Awareness of risk treated with OAT
Duration of treatment known
Frequency of controls known
Awareness of target INR range
Need to follow a specific diet
• Consuming large amounts of salad and vegetables
• Avoid salad and vegetables
• Regular diet of salad and vegetables
• Do not know
Vitamin K content of some foods
• Green salad
• Tomato extract
Management of missed medication dose
Awareness that there are no symptoms of underdosing
Safest over the counter pain medication
• Aspirin (acetylsalicylic acid)
• Other non-steroidal anti-inflammatory drugs
• Do not know
Interaction with OAT
• Regular exercise
• Ginkgo biloba
• Non-prescription drugs
• Moderate intake of alcohol
• Fasting/weight reduction diet
Recognition of emergency situations
• Painful swelling with or without skin discoloration
• Sudden speech disorder
• Black stool (melaena)
• Arm weakness (also temporarily)
• Every cut or injury with bleeding
Important situation to inform others about OAT
• Dental visits
• Before injections
• Any new prescription medication
• Before invasive medical procedures
Overall 13-item score and self-rated knowledge
Factors associated with the 13-item knowledge score oforal anticoagulation therapy (n = 345)
Age (in years)
Gender (women vs. men)
< 10 years education vs. ≥ 10 years education
Good vs poor
Excellent vs poor
Moderate vs poor
history of OAT related complications none vs complications
Fear of bleeding
Fully agree vs disagree entirely
Agree vs disagree entirely
Do not agree vs disagree entirely
Summary of the main results
The results of our survey on patient knowledge show relevant knowledge gaps affecting safe and effective OAT. There was a discrepancy between self-rated knowledge and evaluated actual knowledge. Many participants did not recognize symptoms of emergency situations and had poor awareness of drug interactions, particularly regarding over the counter medication (OTC) and other factors influencing the effects of oral anticoagulants. The overall results are unsatisfying and concerning given that a low level of patient knowledge about OAT is the major cause for bleeding complications [4–6]. Lower levels of education, older age and unawareness about the indication for OAT were associated with lower knowledge about OAT.
Meaning of the results and comparison with literature
More than half of the patients rated their knowledge on OAT as good or excellent. Despite a correlation between self-evaluation and overall score the actual knowledge was overall low and poor in many safety relevant areas. This confirms findings of many smaller studies [15, 18–22].
The majority of patients in our survey knew why they were receiving OAT. Not knowing the indication for OAT was a predictor for poor knowledge. Therefore asking patients why they are taking OAT might be useful to identify patients with an urgent need for instructions. A Spanish study and an Italian study observed that the time spent in the therapeutic range was lower in elderly patients not aware of their indication for OAT [19, 20]. This is in line with our finding that older age is associated with a lower number of correct answers. This was also observed by others [21, 22]. Although one study found that older age was not associated with an increased risk for bleeding complications , others observed a higher incidence of both bleeding and thromboembolic events with advancing age . Cognitive impairment in elderly patients has been associated with inadequate INR control .
Only one third of the participants were aware that patients on OAT should follow a regular diet of salad and vegetables to ensure steady vitamin K supply. It has been shown that eating a diet high in vitamin K, reduces the risk of INR measurements in the subtherapeutic range . A significant proportion (11%) was possibly misinformed and assumed that they should avoid vegetables. Avoiding vegetables to minimize variation in vitamin K intake is not compatible with a healthy diet, as recommended by current guidelines . This dietary restriction is frequently perceived as a significant reduction in quality of life by many patients .
We observed a low awareness of drugs affecting the pharmacodynamics of OAT, particularly with OTC medication and herbal medicines. Popular herbal medicines like ginkgo biloba extracts and St. John’s wort can affect the risk of bleeding [27, 28]. It is known that aspirin and NSAIDs increase bleeding risk, when used in combination with OAT . Most participants did not know which OTC analgesic is safe for patients with OAT and even worse some indicated they would buy aspirin or other OTC NSAIDs. Only 20% were aware that paracetamol (acetaminophen) is considered the safest OTC analgesic for patients on OAT with phenprocoumon [30, 31]. This lack of knowledge is particularly worrisome since two thirds of the participants indicated they would not inform pharmacists about concomitant use of OAT when purchasing OTC medication. However, most participants would inform dentists and physicians before undergoing invasive medical procedures.
More than half of the participants did not recognize emergency situations such as symptoms of stroke or bleeding complications as an emergency situation in which they should seek immediate medical attention. Several studies have demonstrated that awareness of symptoms of stroke and recognition of stroke as an emergency in the general populations is low . A group of patients with increased risk of stroke should have higher awareness in order to take appropriate action, if needed.
Implications for practice
Patients who have already experienced complications related to OAT should be offered instructions or should seek instructions themselves to avoid future complications. However, no higher levels of knowledge were observed in this patient group.
Overall the results of our survey are worrisome and call for structured programs to ensure patient knowledge necessary for safe and effective OAT. It cannot be assumed that one educational intervention is sufficient to maintain necessary knowledge. Although we did not formally assess previous educational activities on OAT, we are aware of the fact that many patients in our sample had been taking OAT for a number of years and had been exposed some form of formal or informal education, regarding their therapy. Therefore periodical reassessment might be necessary. The best strategy for an education program about oral anticoagulation has not been determined yet . An Italian study evaluated the short-term effects of an educational program that did not improve the time spent in the therapeutic range in the short term . In contrast, a French study could show that an education program lowers the complication rate of patients on OAT . A systematic review on the effectiveness of educational interventions to improve the proportion of time spent in the therapeutic range was inconclusive . The included studies were too small to make inferences on complications. Many questions about the best strategy to educate anticoagulated patients remain to be answered. However significant differences in health care systems and the management of OAT will most likely result in different solutions.
Strength and limitations
To our knowledge this is the largest study, assessing patient knowledge about OAT in a representative sample of primary care patients . Previous studies on patient knowledge were conducted in hospitals or with mostly younger patients  often within the frame of patient self-monitoring [9, 34]. The results of these studies can therefore not be generalized to the majority of elderly patients . Studies assessing patient knowledge are prone to selection bias. However, we have a high contact and participation rate and comparison of age and gender did not show statistically significant differences of contacted patients and refusing patients compared to participants. We did not inquire about previous education on OAT since there is no generally established education program for OAT in Germany . Although we did not assess the duration of OAT, we believe that the majority of patients included in this study have been taking OAT for several years.
We demonstrate that patients in the general practice setting have relevant knowledge gaps, potentially affecting safe and effective OAT. GPs should be aware that most patients overestimate their knowledge. There is a need to assess patient knowledge and for effective education program which might need to be repeated periodically. Education programs should focus on drug interactions with non-prescription drugs, dietary advice and recognition of emergency situations. This need for education will persist even when vitamin-K antagonist will be replaced with new drugs.
International normalized ratio
Non-steroidal anti-inflammatory drugs
We are grateful to all participating practices and patients.
The trial was funded by the German Ministry of Health (Project number 2509 ATS 005) within in the “National action plan for drug safety in Germany” (Aktionsplan des Bundesministeriums für Gesundheit zur Verbesserung der Arzneimitteltherapiesicherheit (AMTS) in Deutschland) http://www.akdae.de/AMTS/index.html.
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