
Structure, Function, Testing, and Clinical Implications
If you’ve ever had blood drawn during a bout of illness or a workup for heart disease risk, there’s a decent chance your doctor ordered a C-reactive protein test, usually shortened to CRP. It’s one of the most widely ordered lab tests in the world. CRP is one of the body’s most sensitive early-warning systems for inflammation. Understanding where it comes from, what it does, and how doctors use it reveals a lot about how the immune system operates and why chronic low-grade inflammation has become such a central concern in modern medicine. Warning: doctor talk will follow.
A Protein With a Peculiar Origin Story
CRP was discovered almost by accident in 1930 by William Tillett and Thomas Francis, working in Oswald Avery’s laboratory at Rockefeller University. They were studying patients with acute pneumococcal pneumonia caused by the bacteria Streptococcus pneumoniae and noticed that blood from acutely ill patients caused a specific bacterial substance to clump together. That substance was the “C polysaccharide” in the bacterial cell wall, which gave the protein its name.
For decades CRP was used as a crude yes-or-no indicator of serious infection. It wasn’t until the late 20th century that more sensitive lab techniques revealed its value for detecting the subtle, chronic inflammation now linked to cardiovascular disease and opening a major new chapter in preventive medicine. I had been in practice for several years before I even became aware of CRP.
Shape Matters: The Five-Sided Structure of CRP
CRP belongs to a protein family called the pentraxins, named from the Greek word for “five” because of the protein’s pentagonal shape. Under an electron microscope, CRP looks like five identical subunits arranged in a ring, roughly like five coins fanned into a disc. For history buffs, it resembles the five-star rank worn by General Eisenhower.
Each subunit carries a binding site made of two calcium ions nestled next to a small hydrophobic pocket. This is where CRP does its recognition work: the calcium-dependent sites allow it to grab onto phosphocholine (PC), a molecule found in the membranes of damaged and dying cells, as well as in the outer coatings of many bacteria and fungi. Phosphocholine is so widespread in biology that this single binding chemistry lets CRP respond to an enormous range of threats including microbial invaders and the body’s own dead cells.
CRP doesn’t always exist in this five-subunit ring form. The pentameric version (pCRP) circulates in healthy blood. But at sites of active tissue damage, such as inside an inflamed artery wall, it can break apart into individual monomers (mCRP). These two forms turn out to have strikingly different effects on the immune system.
What CRP Does
It’s tempting to think of CRP as a passive number on a lab report, but it’s actually an active participant in the immune response. It plays at least four major roles.
First, CRP is a pattern recognition molecule. Unlike the antibodies generated by your adaptive immune system which take days or weeks to respond to a specific threat, CRP responds immediately to general molecular patterns shared by pathogens and damaged cells. This makes it a first-responder tool within the innate immune system, the body’s rapid defense network.
Second, once CRP binds to a pathogen or dying cell, it acts as an opsonin, essentially a molecular flag that says “eat this.” Immune cells called phagocytes (macrophages and neutrophils) recognize CRP-coated targets and engulf them, accelerating the clearance of both bacteria and cellular debris.
Third, CRP can activate the complement system, a cascade of proteins that further tags pathogens for destruction. Crucially, CRP appears to stop short of triggering the most destructive steps of that cascade. The net effect is a measured, targeted immune response rather than an all-out inflammatory assault.
Fourth, and this is where things get interesting, the pentameric and monomeric forms of CRP have opposing effects. The pentameric form in circulation is primarily anti-inflammatory, quietly clearing dead cells without triggering unnecessary immune activation. But the monomeric form that appears at sites of tissue damage can amplify inflammation: activating platelets, recruiting immune cells to vessel walls, and stimulating the release of the inflammatory signaling molecule. CRP is neither simply good nor simply bad — it’s context-dependent, functioning as a careful janitor in healthy tissue but potentially fanning the flames in already-inflamed environments.
Fast, Sensitive, and Liver-Made
CRP is produced primarily by liver cells (hepatocytes) in response to immune signals. When immune cells detect infection or tissue damage, they release cytokines, which travel to the liver and switch on CRP production.
One of CRP’s great clinical virtues is speed. Levels can begin rising within four to six hours of an inflammatory event and typically peak within 24 to 48 hours. When the inflammation resolves, CRP falls just as quickly, its half-life in circulation is only about 19 hours. This fast-on, fast-off behavior makes CRP an excellent real-time readout of what the immune system is doing right now, not weeks ago. Because of this early availability, it is referred to as an acute phase reactant.
Under normal, non-inflammatory conditions, CRP in the blood typically measures below 1 milligram per liter (mg/L). During serious bacterial infection or major tissue injury, levels can spike above 400 mg/L — a several-hundred-fold increase. CRP also has a practical advantage for testing: it doesn’t fluctuate throughout the day, and fasting is not required before a blood draw.
The Many Uses of CRP in Clinical Medicine
The oldest application of CRP testing is detecting and monitoring bacterial infection. Very high values — generally above 100 mg/L — strongly suggest bacterial rather than viral infection, since viruses tend to provoke a much more modest CRP rise. In sepsis (the life-threatening systemic response to infection), CRP is one of several markers used to assess severity and track the response to treatment.
CRP is also routinely used to monitor autoimmune diseases. In rheumatoid arthritis, CRP is included in standard disease activity scoring tools. Tracking CRP over time helps clinicians judge whether treatments like disease-modifying drugs are working. One notable exception: in systemic lupus erythematosus (SLE), CRP often stays surprisingly low even during active flares.
Perhaps the most debated expansion of CRP testing in recent decades is its role in cardiovascular risk assessment. That story begins with the recognition that atherosclerosis, the plaque buildup inside artery walls, is fundamentally an inflammatory process, not just a plumbing problem caused by too much cholesterol. As that insight took hold in the 1990s, researchers began asking whether CRP could predict heart attack risk the way cholesterol does.
The answer was yes, but only with a more sensitive test. Standard CRP assays can’t detect levels below about 10 mg/L, which is fine for infections but misses the chronic low-level inflammation relevant to cardiovascular risk. A newer high-sensitivity CRP test (hs-CRP) can measure levels as low as 0.01 mg/L. Using hs-CRP, researchers found that even modest CRP elevations, within the range once considered entirely normal, carry meaningful cardiovascular risk.
The American Heart Association and the CDC use these hs-CRP thresholds for cardiovascular risk: below 1 mg/L is low risk; 1 to 3 mg/L is intermediate risk; above 3 mg/L is higher risk. A large UK Biobank analysis of nearly 450,000 people found that individuals with hs-CRP above 3 mg/L had a 34% higher risk of major cardiovascular events and a 61% higher risk of cardiovascular death compared to those below 1 mg/L.
The landmark JUPITER trial demonstrated that patients with low LDL cholesterol, but elevated hs-CRP (above 2 mg/L) still benefited substantially from statin therapy — in terms of reduced heart attacks and strokes. This reframed how cardiologists think about inflammation as a cardiovascular target independent of cholesterol levels.
Beyond infection, autoimmune disorders, and heart disease, elevated CRP has been linked to type 2 diabetes, metabolic syndrome, chronic kidney disease, COPD, depression, and neurodegenerative diseases, all conditions where chronic low-grade inflammation is increasingly recognized as a contributing factor rather than just a side effect.
Measuring CRP: The Standard Test vs. the High-Sensitivity Test
CRP testing is straightforward, just a standard blood draw, no fasting required. Modern automated lab analyzers make it fast and inexpensive, which explains why it shows up so often in clinical workups.
The standard CRP test is the workhorse for detecting acute infection and monitoring inflammatory flares in hospitalized patients. The hs-CRP test uses more sensitive techniques and is the test used for cardiovascular risk assessment.
Because hs-CRP can fluctuate modestly from day to day, cardiovascular guidelines recommend averaging two measurements taken about two weeks apart. Acute illness, recent injury, or even a hard workout can temporarily elevate hs-CRP and produce a misleading result.
Several factors can push CRP higher independently of the disease in question: obesity, smoking, high blood pressure, metabolic syndrome, low HDL cholesterol, and chronic low-grade infections such as gum disease. Age also gradually raises baseline CRP. On the other side, moderate physical activity, weight loss, and statins are all associated with lower CRP — which partly explains the broader cardiovascular benefits of statin therapy beyond cholesterol reduction.
What CRP Can’t Tell You
For all its usefulness, CRP is a nonspecific marker. A reading of 50 mg/L is consistent with a kidney infection, an autoimmune flare, a recent heart attack, or an abdominal cancer. CRP tells you that inflammation or tissue damage is happening somewhere; it doesn’t tell you where or why. Clinical context including symptoms, medical history, and other lab results, is essential for interpretation.
There’s also a genuine unresolved debate about whether CRP elevation actually causes cardiovascular disease or is simply a marker of underlying inflammatory risk. Animal studies in CRP-deficient or CRP-enhanced models have produced inconsistent results. Mendelian randomization studies in humans, a statistical technique that uses genetic variants to approximate a randomized experiment, have generally not supported CRP as a causal driver of heart disease, suggesting it may be more of a reaction than a root cause.
Finally, hs-CRP testing, despite strong evidence, remains underused in primary care, particularly in primary prevention. The 2024 European Society of Cardiology guidelines for chronic coronary syndromes did recommend assessing hs-CRP in patients with suspected coronary artery disease, which reflects accumulating evidence for its utility, but broader implementation lags behind the science. I have to admit, when I was still in active practice, I was unaware of the role of hs-CRP in primary prevention. At the time, it was generally thought to be of use in secondary prevention—actions taken after an initial event. Be sure and ask your doctor about it.
CRP is, in the end, a remarkably versatile tool — a protein that has been doing immune surveillance since long before medicine had a name for it, and one that continues to find new clinical relevance with each decade of research.
Medical Disclaimer
The information provided in this article is intended for general educational and informational purposes only and does not constitute medical advice. It should not be used as a substitute for professional medical advice, diagnosis, or treatment.
Always seek the guidance of a qualified healthcare provider with any questions you may have regarding a medical condition or treatment. Never disregard professional medical advice or delay seeking it because of something you have read here.
If you are experiencing a medical emergency, call 911 or your local emergency number immediately.
The author of this article is a licensed physician, but the views expressed here are solely those of the author and do not represent the official position of any hospital, health system, or medical organization with which the author may be affiliated.
Image generated by the author using ChatGPT
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Who Gets to Decide? The Modern Battle Over Books in America
By John Turley
On June 19, 2026
In Commentary, Politics
If you thought book banning was a relic of the past, think again. The United States is experiencing the most intense wave of book challenges in modern memory. Over the last four years, thousands of books have been removed from school and library shelves, sparking a national debate about parental rights, free expression, education, and the role of government.
At the center of the controversy is a simple but powerful question: Who gets to decide what children and communities are allowed to read?
We were casually looking for books to read with our grandson this year. He loves baseball so we were looking for books on that topic. Somehow we got on a site about banned books and, yes, there was a baseball story on the list, curiosity got us. The book is Baseball Saved Us by Ken Mochizuki and Dom Lee. This is the story about a baseball field that was created in a Japanese internment camp in during World War II and the prejudice they faced when they returned home after the war. The story, written on a fourth grade reading level, is about how the boys played baseball during their internment and how it helped them to survive. This is a banned book?? Why??
This made us wonder what it means to be on a “banned book list”. Just because it’s on the list does every library or school have to ban it? The answer is no, thank goodness. Members of library boards and school boards and parents play an important role and they have a lot to consider. Here are some interesting details about book banning in its current evolution.
The Scale of the Movement
The numbers are striking. According to PEN America, nearly 23,000 book bans have occurred in public schools since 2021. During the 2023–24 school year alone, more than 10,000 individual book bans were recorded. The following year saw nearly 7,000 additional bans affecting more than 3,700 unique titles.
Florida has led the nation in book removals for three consecutive years, followed by Texas and Tennessee. The American Library Association (ALA) documented more than 4,200 unique titles challenged in 2025, making it one of the highest years ever recorded.
Not every challenge results in a permanent ban. Some books are removed temporarily while review committees evaluate complaints. Others are eventually restored to shelves. Yet the sheer volume of challenges has significantly reduced access to books for many students and library users.
Supporters argue these actions protect children from inappropriate material. Critics view them as a growing campaign of censorship.
Which Books Are Being Targeted?
The books most frequently challenged share common themes.
According to the ALA, many complaints focus on books that discuss race, racism, gender identity, sexuality, or LGBTQ+ experiences. Others involve sexual content, abuse, violence, or mental health issues.
Among the most challenged books in recent years are Gender Queer by Maia Kobabe, The Perks of Being a Wallflower by Stephen Chbosky, Looking for Alaska by John Green, and several novels by Sarah J. Maas.
Classic works have also been caught in the controversy. Schools and districts in several states have removed or restricted books such as The Bluest Eye by Toni Morrison, The Kite Runner by Khaled Hosseini, and even George Orwell’s 1984.
Critics of the banning movement note that many of these books have been available in schools for years or even decades. They argue that the current challenges are less about newly discovered concerns and more about broader cultural and political disagreements.
Who Is Driving the Challenges?
One of the most significant developments is the changing source of complaints.
The ALA reports that in 2025, 92 percent of book challenges originated from organized groups, government officials, or political activists rather than individual parents. Twenty years earlier, most challenges came from local citizens raising concerns about specific books.
This shift suggests that book challenges have become part of a larger political movement rather than isolated local disputes.
Among the most visible organizations is Moms for Liberty, founded in Florida in 2021. Originally focused on opposition to COVID-19 school policies, the group later turned its attention to curriculum issues and library books. It now claims chapters in dozens of states and has become a major force in school board elections and library controversies.
Other organizations, including No Left Turn in Education, Citizens Defending Freedom, and various state-based groups, have pursued similar goals. These organizations often share lists of books to challenge, provide guidance to local activists, and coordinate campaigns across multiple communities.
Supporters describe these efforts as parental advocacy. Critics see them as organized attempts to impose political and ideological restrictions on public education.
The Political Connection
The book-banning movement has become closely associated with broader conservative politics, particularly the MAGA movement.
Moms for Liberty has maintained ties with the Heritage Foundation, the conservative think tank that developed Project 2025. The Heritage Foundation has sponsored Moms for Liberty events and honored the organization with awards recognizing its activism.
The relationship became even more visible when Moms for Liberty co-founder Tiffany Justice left the organization to lead the Heritage Foundation’s parental-rights initiative.
Former President Donald Trump has also embraced many of the same themes. He appeared at a Moms for Liberty national summit and has frequently criticized educational institutions, libraries, and schools that he believes promote what he describes as inappropriate or politically biased material.
Supporters view these alliances as part of a broader effort to restore parental control over education. Opponents argue they demonstrate that book challenges have become deeply intertwined with national political agendas.
Project 2025 and Libraries
Much attention has focused on Project 2025, the policy blueprint produced by the Heritage Foundation.
The document calls for stronger action against what its authors characterize as inappropriate materials in schools and libraries. Critics have highlighted language suggesting that educators and librarians who provide access to certain materials could face legal consequences.
Supporters argue that such proposals are intended to protect children from explicit content. Opponents contend that they would create a chilling effect, discouraging educators and librarians from offering books dealing with controversial subjects.
The debate reflects a broader disagreement about where the line should be drawn between protecting minors and preserving intellectual freedom.
How Libraries and Schools Are Responding
Responses vary widely across the country.
Some school districts remove challenged books immediately. Others establish review committees consisting of teachers, librarians, administrators, parents, and sometimes students. These committees examine books in their entirety before making recommendations.
Public libraries have generally been more resistant to removing books. Most rely on formal collection-development policies and challenge procedures designed to balance community concerns with principles of intellectual freedom.
Many libraries have retained challenged books after review, arguing that public libraries serve diverse populations and that parents should make reading decisions for their own children without limiting access for others.
At the same time, librarians in some states report increasing pressure from elected officials and advocacy groups. Concerns about funding, employment consequences, and potential legal liability have led some libraries to avoid purchasing controversial titles altogether.
Critics refer to this phenomenon as “preemptive censorship” because books disappear before formal challenges even occur.
State Governments Enter the Fight
Several states have moved beyond local challenges and enacted statewide policies.
Utah, South Carolina, and Tennessee have adopted mechanisms that allow certain books to be removed from schools statewide. Florida has expanded parental authority over educational materials and library collections.
Supporters argue these measures provide consistency and protect children across entire states. Critics counter that statewide restrictions eliminate local decision-making and reduce access to books for students whose families may have no objections to the material.
The controversy has occasionally reached dramatic levels. In Randolph County, North Carolina, county commissioners dissolved the public library board after it refused to remove a children’s book featuring a transgender character.
Such disputes illustrate how library policy has become a flashpoint in cultural conflicts.
The Courts Push Back
Many of these policies have faced legal challenges and the results have been mixed.
In Iowa, a federal judge blocked portions of a state law that prohibited books containing descriptions of sexual activity, ruling that the restrictions likely violated First Amendment protections. In the Rutherford County, Tennessee case, the first legal challenge to that state’s expanded book statute — a federal judge declined to issue a preliminary injunction, writing that a school board “has not prohibited students from reading the books or acquiring them elsewhere; instead, it has merely opted not to carry them on school library bookshelves.”
Courts have often struggled to balance competing interests. School boards possess significant authority over educational materials, while students have constitutional protections related to access to information.
The legal outcomes remain uncertain, but the judiciary has become one of the primary battlegrounds in the debate.
Voters Respond
School board elections have become another arena for the conflict.
In several Texas districts during 2025, voters removed incumbents who had championed aggressive book-removal policies. Similar results appeared in other states, suggesting that many voters are uncomfortable with the scope of current restrictions. At the same time, candidates supporting stricter controls continue to win elections in other communities.
The mixed results indicate that Americans remain deeply divided on the issue.
A Growing Countermovement
Opposition to book bans has generated its own political response. Organizations such as PEN America, the Authors Guild, the ALA, and numerous local advocacy groups have organized campaigns defending intellectual freedom. Several states have considered legislation designed to make book removals more difficult.
Minnesota, for example, has considered legislation that would prohibit the removal of books based primarily on ideological objections and would place greater authority in the hands of professional librarians.
Supporters argue such laws protect access to information. Critics contend they diminish parental influence and local control.
The Bottom Line
The modern book-banning movement is unlike anything seen in recent decades. Its scale is unprecedented, its organization is sophisticated, and its connections to broader political movements are well documented.
Supporters view the effort as a legitimate exercise of parental rights and community standards. Critics see it as an organized campaign to restrict access to ideas, experiences, and viewpoints that some groups find objectionable.
The debate is unlikely to disappear anytime soon. It touches fundamental questions about education, democracy, free speech, and the role of public institutions.
Who should decide what belongs on library shelves? Parents? Librarians? Teachers? School boards? Legislatures? Courts?
Americans have not reached a consensus on those questions. Until they do, the battle over books is likely to remain one of the most visible fronts in the nation’s ongoing culture wars.
Illustration generated by author using Chat GPT
Sources
PEN America — Book Bans Overview
PEN America — The Normalization of Book Banning (2024–25 Report)
American Library Association — Censorship by the Numbers
ALA — Most Challenged Books
NPR — ALA Releases 2025 Most Challenged Books
NPR — PEN America 2024–25 Report
Authors Guild — Voters Reject Book Restrictions, 2025
Washington Post — Trump, Moms for Liberty, Heritage Foundation
New Jersey Monitor — M4L Summit and Project 2025 Ties
GLAAD — Moms for Liberty and Book Bans
EveryLibrary Institute — Project 2025 and Libraries
I Love Libraries — Book Challenges Update
Freedom to Learn Foundation — 2025 State of Book Banning