Aspirin Resistance Prevalence: A Landmark Pakistani Study Reveals the Numbers

Aspirin Resistance Prevalence

Aspirin Resistance Prevalence: A Landmark Pakistani Study Reveals the Numbers

Last Updated: July 31, 2025

For decades, low-dose aspirin has been hailed as a wonder drug—a simple, inexpensive pillar of cardiovascular disease prevention. It’s prescribed to millions to reduce the risk of heart attacks and strokes. Yet, a hidden and dangerous phenomenon known as “aspirin resistance” threatens this protection, leaving a significant number of patients vulnerable despite their daily adherence. The most pressing question for clinicians and patients alike has been: just how common is this problem?

A landmark doctoral thesis from Pakistan provides one of the clearest answers to date. By meticulously studying a large cohort of heart patients, the research quantifies the aspirin resistance prevalence and explores the profound clinical implications of treatment failure. This analysis will walk you through the study’s robust methodology, reveal its headline findings, and place them in a global context, offering an in-depth look at a critical issue in modern cardiology.

What is Aspirin Resistance and Why Does It Matter?

Before diving into the numbers, it’s crucial to understand the stakes. Aspirin works by inhibiting the COX-1 enzyme in platelets, preventing the formation of thromboxane A2, a molecule that signals platelets to clump together and form clots. When a person is “aspirin resistant,” this antiplatelet effect is diminished or absent.

From the thesis introduction:

“Even though the aspirin has significantly established use in ischemic conditions, a significant proportion of patients taking antiplatelet doses of aspirin fail to respond appropriately to these drugs and encounter repeated uninvited cardiovascular adverse effects. This trend is commonly denoted as ‘aspirin resistance or aspirin non-responsiveness or aspirin treatment failure’.”

This failure is not a trivial matter. The research underscores that the consequences are severe, transforming a manageable risk into a critical threat.

Key Clinical Risks:

  • Patients identified as aspirin non-responders carry a considerably higher risk of ischemic vascular attack.
  • Meta-analyses cited in the study show that aspirin-insensitive patients have a significantly higher danger of vascular complications.
  • The Heart Outcomes Prevention Evaluation (HOPE) study suggested that aspirin-resistant patients had a 3.5-fold greater risk of cardiovascular death and a two-fold higher risk of myocardial infarction.

Understanding the aspirin resistance prevalence is, therefore, the first step in identifying this high-risk population and developing strategies to protect them.

The Gold Standard: How the Study Measured Aspirin Efficacy

To provide a credible answer on prevalence, the study’s methodology had to be impeccable. The researchers, led by Dr. Mudassar Noor, employed the gold standard technique for assessing platelet function, ensuring their results were both accurate and reliable. This scientific rigor is what gives the study’s findings their weight.

The investigation was a cross-sectional analytical study involving 384 Pakistani patients with ischemic heart disease, all of whom had been taking daily aspirin for at least seven days.

Light Transmission Platelet Aggregometry (LTA)

The chosen method was Light Transmission Platelet Aggregometry (LTA), which is widely considered the most authentic and referenced test for platelet activity.

From the thesis methodology:

“To assess the efficacy of aspirin we selected the world wide gold standard considered method ‘LTA’. This method analyzes the platelet response upon exposure of different agonists… Since we were evaluating the effectiveness of aspirin, so we chose the AA as an agonist, which is directly related to aspirin’s action.”

Here’s how LTA works:

  1. A patient’s blood is spun in a centrifuge to separate the platelet-rich plasma (PRP).
  2. A light beam is passed through the PRP sample. Initially, the dense platelets block most of the light.
  3. An “agonist”—in this case, arachidonic acid (AA), the substance aspirin is meant to block—is added to the sample.
  4. If aspirin is working effectively, the platelets will not react to the AA and will remain separated, continuing to block the light.
  5. If the patient is aspirin-resistant, the platelets will clump together (aggregate) in response to the AA. This clumping clears the plasma, allowing more light to pass through.
  6. The machine measures this increase in light transmission as a percentage of aggregation. For this study, aggregation of greater than 20% was the cutoff to define aspirin resistance.

This meticulous, lab-based approach removes guesswork and provides a quantitative measure of aspirin’s biological effect, making the resulting prevalence data highly credible.

The Final Tally: The Prevalence of Aspirin Resistance

After analyzing all 384 patients using the LTA method, the study produced a clear and definitive number for the aspirin resistance prevalence within this large cohort.

From the thesis results:

“Out of 384 patients 13.8% cardiovascular disease patients (n=53) showed >20% aggregation and were labeled as aspirin resistant cases. The remaining 331 patients (86.2%) had <20% platelet aggregation and were categorized as aspirin responders.”

This headline finding means that approximately 1 in 7 patients on daily aspirin for heart disease were not receiving the expected antiplatelet protection. While the majority of patients did respond, a 13.8% failure rate represents a substantial number of individuals who remain at high risk for life-threatening thrombotic events.

A Stark Difference in Platelet Activity

The study went further than just classifying patients. It measured the degree of platelet aggregation, revealing a vast chasm between the two groups.

  • Aspirin Responders: This group showed a mean platelet aggregation of just 3.52%.
  • Aspirin Resistant Patients: This group had a staggering mean platelet aggregation of 60.60%.

This enormous difference confirms that aspirin resistance isn’t a minor variation in response; it’s a profound and near-complete failure of the drug’s primary mechanism of action in affected individuals.

Putting the 13.8% Figure in a Global Context

A single study, no matter how well-conducted, provides one piece of a larger puzzle. The discussion section of the thesis contextualizes its findings by comparing them to previous research, particularly within the South Asian subcontinent.

From the thesis discussion:

“Previously two studies have been conducted in to estimate the incidence of aspirin resistance in Pakistan. Akhtar and colleagues in their cross sectional prospective study revealed 12% aspirin resistance… There was no statistical noteworthy difference when it was compared to our results… Faheem et al… concluded 47.1% aspirin resistance in their sample population. These findings are significantly different than ours.”

This comparison highlights a critical point: the reported aspirin resistance prevalence can vary widely. Dr. Noor’s 13.8% is very close to the 12% found by Akhtar et al., suggesting this range may be accurate for the Pakistani population when using certain testing methods. The much higher 47.1% figure from the Faheem et al. study was attributed to a different measurement technique (whole blood aggregometry) and a smaller sample size, which can lead to more variable results.

When compared to studies in India, which found prevalence rates of 23.7% and 36%, the 13.8% figure from this study appears to be on the lower end, further emphasizing that prevalence rates can be influenced by population genetics, diet, lifestyle, and study methodology.

Conclusion: A Significant and Under-recognized Threat

This comprehensive study solidifies the phenomenon of aspirin resistance as a major clinical concern. With a prevalence of 13.8%, it affects a substantial minority of cardiovascular patients who believe they are protected but remain at high risk. The research demonstrates the vital importance of robust, standardized testing like LTA to accurately identify these non-responders. For clinicians and patients, this data is a powerful reminder that medication efficacy cannot be assumed. Awareness and further investigation are crucial to closing this dangerous gap in cardiovascular care.

Author Bio: This analysis is based on the doctoral research of Dr. Mudassar Noor, conducted at the Department of Pharmacology & Therapeutics, Army Medical College, a constituent college of the National University of Medical Sciences (NUMS) in Rawalpindi, Pakistan.

Source & Citations

Disclaimer: Some sentences have been lightly edited for SEO and readability. For the full, original research, please refer to the complete thesis PDF.

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