Mayo Clinic has multiple laboratory tests available to help us diagnose rheumatologic conditions: rheumatoid factor, ANA, ESR, CRP and more. It’s gotten quite confusing trying to decide which tests to order when we suspect a specific rheumatologic condition. When are these tests helpful? How specific are these tests for the condition we're trying to diagnose, and what does it mean when we have a positive result but a low titer test result in an asymptomatic patient? In this podcast, we answer these questions and more with our guests, Ashima Makol, M.B.B.S. , and Matthew J. Koster, M.D. , both from Mayo Clinic Rheumatology.
Rheumatologic problems are some of the most common health conditions we see as primary care professionals. They can become frustrating for both the provider and the patient, as in many cases it may take months and sometimes even years to establish a correct diagnosis. There are a variety of new tests available to help us confirm a diagnosis, as well as multiple new and effective treatment options. This episode is part of a seven-episode miniseries on Mayo Clinic talks dedicated to rheumatologic health problems to aid in the recognition, diagnosis, and treatment of your patients. Please find these additional episodes where you listen to podcasts or on CE.mail.edu. This is Mayo Clinic Talks, a curated weekly podcast for physicians and healthcare providers. I'm your host, Darryl Chutka, a general internist at Mayo Clinic in Rochester, Minnesota. We have multiple laboratory tests available to help us diagnose rheumatologic conditions rheumatoid factor, ANA, ESR, CRP, and many more. And it's gotten quite confusing, trying to decide which tests to order when we suspect a specific rheumatologic problem. When are these tests helpful? How specific are these tests for a condition we're trying to diagnose? What does it mean when we have a positive but low tier test in an asymptomatic patient? In today's podcast, we'll review the various rheumatologic tests available and we'll answer these questions and more with our guests, Doctor Ashma McCole and Doctor Matthew Koster, both from the division of Rheumatology at the Mayo Clinic. You're listening to Mayo Clinic Talks. Matthew Ama, welcome and thank you for joining me today. Uh thank you for having us. You've got essentially a alphabet soup of tests available for us now. I've been around long enough, so when I first started practice, we basically had a sedimentation rate, rheumatoid factor, and ANA. That was it. Quite a few more now. So, let's tackle some of these that we come in the order and find out what they actually check on and When we can use them. Let's start with some inflammatory markers, the uh sedimentation rate and CRP. What are these tests measuring? So the inflammatory markers, the ESR and CRP are really a very non-specific marker of what we call the acute phase response, and this happens in various conditions that are associated with what we call inflammation. When we talk about inflammation, somehow that is equated to systemic autoimmune rheumatic diseases, but uh one thing we want to keep in mind is that inflammation is a part of infections, trauma, infarction, malignancy, and so many other processes. So when we, when we check these markers, that clinical history, physical examination, the perspective in which we're testing these becomes very, very relevant. ESR indirectly represents the amount of fibrinogen being produced in the body, while the C-reactive protein is indirectly a marker of the amount of IL-6 production in the body. And in different processes, depending on what the inflammatory milieu is or what inflammatory cytokines are driving these particular proteins up or down, your sed rate can climb up or CRP can and sometimes together and sometimes not. Are they pretty much equivalent? Uh, is there a case where one might be elevated, the other one is not, or do they pretty much go up and down at the same rate? As Doctor McCall was mentioning, the sedimentation is more of an indirect measure, so really it's checking proteins, so fibrinogen and also things like immunoglobulins, right? So, if you want to understand the sedimentation rate itself and what it's checking, so it's looking at how fast red blood cells drop within a certain amount of time, 1 hour. So that's why the units is millimeters per hour. Red blood cells normally have a negative charge, so they'll repel each other. So if you're thinking about uh throwing 100 pennies into the water and have them drop down to the the sand, versus taking a stack of pennies and dropping that through the water and seeing how that goes. The stack of pennies is going to go much faster. So these increased proteins, fibrinogen or immunoglobulins, those are positively charged and so they'll kind of bring the red blood cells together and make them drop in what's called a roule formation or a stacked pattern. So that's why the stacked pennies. So there are some times in which these things will be elevated, high fibrinogen values, high immunoglobulins. That will make the sedimentation rate very high. So those are certain circumstances in which the immunoglobulin production can be high, whether it's a polyclonal process like rheumatic disease, or a monoclonal process like multiple myeloma, for instance. In addition, other things that can drive up fibrinogen and proteins are things like chronic kidney disease, chronic liver disease. So those are things in which the sedimentation rate can be increased, but the C reactor protein wouldn't. Also, as you age, you can end up having an increase in the sedimentation rate. So the, the upper limit of normal for um males is roughly their age divided by 2. So if you have an 80 year old male, his upper limit of normal would be about 40. For females, it's about age plus 10 divided by 2, so theirs would be about 45. Other things to consider are things like hyperglycemia or diabetes. So, the higher the glucose, you could have glucose that'll tag to the red blood cells and make them fall faster. So sometimes we see what's called discordant, high sedimentation rate, normal C reactive protein, and so that's when you need to investigate those other issues, hyperglycemia, increased proteins like monoclonal proteins, or other things like kidney or liver disease. So these tests measure inflammation and I assume that they can be used both in assisting us with a diagnosis as well as monitoring disease activities. Is that correct? That is correct. To come back to that point of discordance as we were talking about earlier, in particular rheumatic conditions, we see that both of these markers go up in parallel, like in particular with people who have polymyalgia rheumatica or rheumatoid arthritis, so. cell arthritis, we see a significant elevation in both the ESR and the CRP going up together and as patients improve with regards to the symptoms or we're seeing the medication efficacy kick in, we often see normalization of the ESR and CRP often concordantly. But then there are some unique situations in which these inflammation markers tested together can be very helpful, like in patients who have lupus in particular. So just the way the pathophysiology works, there's a very high type one interferon response and that suppresses production of IL-6 by hepatocytes and thus the CRP is relatively suppressed in patients with lupus who are having a flare, but their, their SE rate is typically very high. On the other hand, if you see a pretty impressively elevated CRP in a lupus patient, we should strongly suspect infection bringing that CRP up. So that helps in the differential diagnosis of some of these conditions and rheumatology as well. OK. Let's talk about rheumatoid factor. What's this test measuring? Yeah, so rheumatoid factor, really what that's looking at is trying to quantify an autoantibody, where the immunoglobulin itself, the autoantibody is addressed to a normal immunoglobulin. And so if you're thinking about immunoglobulin structure, think of kind of the structure of a Y, like the letter Y. You have kind of a a common base and then two arms. And so the autoantibody that's produced, rheumatoid factor, typically IGM rheumatoid factor is the most pertinent, ends up addressing or responding to that base portion of the Y of an immunoglobulin IgG. So that can be produced in many different circumstances, one of which is rheumatoid arthritis, but as we'll discuss in a little bit, there are also some other conditions that rheumatoid factor can be positive in. OK? Now, we know there are rheumatoid factor negative patients with rheumatoid arthritis. What, what does the fact that this test is negative imply about their arthritis? Anything at all? Is it any different? Yes, so first, from a diagnosis perspective, some patients have a positive rheumatoid factor, but other patients can have a positive CCP antibody, which is a different blood marker for rheumatoid arthritis. And though the rheumatoid factor might be very much more sensitive, it is less specific for rheumatoid arthritis and the specificity of this other marker, the anti-CCP antibody. It is over 90%. So it could be that a patient is 0 positive and may carry the rheumatoid factor and or the CCP or in some circumstances, they may carry neither of those antibody and something that we call sero negative rheumatoid arthritis, where they have classic clinical symptoms, examination findings, supportive imaging in. Combination with a negative and CCP, they still have rheumatoid arthritis just not with the typical blood markers. OK. But then when they have a positive rheumatoid factor or a CCP antibody, that entails a higher risk for extraracticular manifestations, radiographic progression, and overall a more severe disease, um, and trajectory. So, Matthew, you uh indicated that there are other conditions that can have an uh positive rheumatoid factor. What, what are some of those other conditions? Yeah, so there, there's actually several other conditions that can lead to a positive rheumatoid factor. So hepatic disease can end up having this being present, whether it's autoimmune liver disease or other. Things like lupus, scleroderma, mixed connective tissue disease, Sjogren's syndrome, these can also have low to modest titers of rheumatoid factor and still be within the spectrum of autoimmune diseases. And then things like infections, particularly chronic viral infections like hepatitis B, particularly, hepatitis C, HIV, and then other more serious things like endocarditis, for instance. And then some malignancies like lymphoma can also have these things be present. So as Ama was mentioning, rheumatoid factor may have some sensitivity and by sensitivity, it's negative, it's less likely. If it's positive, it's not very specific to that has to be rheumatoid arthritis because these other conditions can also have that antibody be present. Whereas the CCP antibody has a higher specificity. that if that is present, it's more likely that you end up having rheumatoid arthritis as as opposed to other conditions because there's fewer conditions, although chronic infections can stimulate CCP production as well, but overall, there's less conditions beyond rheumatoid arthritis that would generate a positive CCP antibody. OK. I've had a few patients as they get on in their age, their rheumatoid arthritis either goes in remission or resolves. Does their rheumatoid factor stay positive? The rheumatoid factor can definitely vary with the disease course. It can fluctuate up and down in the tighter, and in rare circumstances it can even become negative, but we typically don't follow that titer over time. Beyond its face value of being positive or negative, it really doesn't help us monitor disease activity, which is based on the clinical symptoms and clinical manifestations primarily. A, you mentioned CCP antibodies in relation to rheumatoid arthritis. Let's talk about those. What are those tests measuring? Yeah. So yeah, in rheumatoid arthritis, we see that uh the citrullation of certain peptides within the body. And in particular, this is seen in at a higher prevalence in patients who are smokers in particular that this uh the smoking citrullinates certain proteins within the lungs. It has also been seen within the periodontal lining and some of these patients are Predisposed to developing this anti-CCP antibody, which is a blood marker for rheumatoid arthritis. Sometimes we see this marker just present in smokers without any evidence of inflammatory arthritis, so that smoking history becomes a little relevant. It does predict a future risk of potentially developing rheumatoid arthritis if they continue to smoke. So that is technically a modifiable risk factor for rheumatoid arthritis in those situations. So can you have a positive CCP antibody and negative rheumatoid factor? Is that possible? Yep, certainly. And you can have positive rheumatoid factor and negative CCP. You can have positive CCP with negative rheumatoid factor. And in a subset of people, as Asma mentioned, you can have what's called sero negative inflammatory arthritis, where they'll be negative for both. Now, a couple of things to, to mention in that context. So, if you're talking about just background health Normals, right, normal population who doesn't have rheumatoid arthritis. There's going to be a higher prevalence of patients who can have a positive rheumatoid factor. We're talking on about 5 to 10, maybe up to 15% of the population as the likelihood of rheumatoid factor positivity increases with age compared to about 1 to 5% of the normal healthy population can have a positive CCP antibody. Some of those patients may have a positive antibody years before they develop disease. So there are patients who may end up not having clinical symptoms currently, but then later on may develop clinical features of disease. But having a positive antibody does not mean that you are going to 100% develop inflammatory arthritis. The other thing is that if you have inflammatory arthritis features, but negative rheumatoid factor in CCP, that's where ideally working with a rheumatologist to say, what are the other entities that could be present? Could it be lupus? Could it be something like within the family of spondyloarthritis? Could it be something crystalline like gout or pseudo gout, or could it be atypical presentations of other rare conditions like incavascular? So those are things that need to be delved into within the clinical, physical exam, imaging studies, etc. OK. Well, let's turn to uh ANA or anti-nuclear antibody. What are we measuring with this test? So just as the name suggests, suggests it's an anti-nuclear antibody. So this is an antibody that targets various different nuclear components and that might be the DNA, the RNA, the histones, the nucleolus, the centromere. And a wide variety of a combination proteins within the nucleus. And what conditions are associated with a positive ANA. So ANA is really a task that keeps us rheumatologists in business. I can tell you that. It is just a very interesting marker that may have absolutely no clinical relevance because it Be present in about 15 to 20% of the general population without absolutely having no clear background of autoimmune rheumatic disease, but then it can be a starting point for testing for many, many different autoimmune diseases, in particular lupus. So in systemic lupus erythematosis, 99% of people are positive for ANA. So if you don't have a positive ANA, there's a very high likelihood that you don't have lupus. But there are some nuances to that because in patients who have just cutaneous lupus or lupus nephritis, that is biopsy proven, some of those patients might actually be ANA negative and it A very, very small proportion, but technically only in a few of those circumstances this is possible. Yet the ANA can be present in other autoimmune rheumatic diseases like Sjogren's, mixed connective tissue disease, systemic sclerosis or scleroderma, inflammatory myopathies, and a whole host of other autoimmune conditions like those of the thyroid, like Hashimoto's or Graves. Disease you can have autoimmune hepatitis, a primary biliary cirrhosis, ulcerative colitis, and the list goes on. But the ANA also increases with aging, so simply immune senescence, where our body is just not capable enough now with an aging immune system to get rid of some of these, these antibodies that are being produced on a daily basis. We can see about. 15 to 20% prevalence in a patient above the age of 65, very similar to what we see with the rheumatoid factor as well. So I think you pretty much answered my next question. I have an occasional patient who usually has pretty classic osteoarthritis, but somehow got an ANA ordered and it came back positive, usually low tighter, so I assume this means absolutely nothing. I think from from that perspective, if they have a low tighter ANA and you have a low clinical suspicion, then I don't think that that should raise a high concern for something like lupus. But part of it too is I think to comment back on kind of negative ANA rule out lupus, it's also how is the ANA done? So that there's different mechanisms of testing for the ANA. So when you're looking at something in the computer or something that someone's ordered, if you see a numerical value like 1.6, 3.4, 8.0, that was done by what's called Eliza method, that's largely computer generated, whereas the more specific is immunofluorescence, typically by something called Hep 2 substrates, certain type of cell line. So if you have a high clinical suspicion for something like a connective tissue disease or lupus and someone checked an EISA antibody and it was negative or equivocal, then following it up with a more specific test like the ANA byEP 2 substrate, the immunofluorescence is helpful. The titers for that. So a positive test versus negative test, we really haven't talked about cut-off thresholds, but clinically speaking, if it's stronger, so the second number within that tighter, the 1 to 40, 1 to 80, 1 to 160, so it keeps moving out to higher titers the further you go out. Once you get around 1 to 160 and sure around 1 to 320 and higher for that second number, the likelihood of false positivity decreases slightly. So it increases the pertinence. But part of the difficulty is trying to say, what's your, what we call a pre-test probability. If you think they really don't have connective tissue disease, then don't check the test because you will find some of these patients who are positive at low titers, and then you really have to go down and dig and say, is it gonna be something, does it provide some Healthcare associated anxiety, cause now they see a positive test and they're worried cause they Google lupus. And so sometimes really understanding what you think the likelihood of diseases is important even before ordering the test. OK. Let's talk about antineutrophil cytoplasmic antibodies or uh ANCA ANCA. You, I think one of you uh mentioned this test a little while ago. What what is this test? Yeah, so anti-neutrophil cytoplasmic antibodies, the people who name these tests are very helpful in outlining what they are. So similar to the ANA, this is looking for autoantibodies against the cytoplasmic components of neutrophils, right? So that, that's kind of evident within the test. But essentially, when we're looking at these types of antibodies, again, there's kind of two ways of doing it. There's the Eliza methodology that I had mentioned for the ANA, that's really looking at the specific antibodies to certain proteins. The ones that are most pathologic or important is something called protanase 3 or PR3 is the acronym, or something called myeloperoxidase, MPO is the acronym. The immunofluorescent staining pattern where they actually look under the cell type and look for the staining, that is something called C anka, which is cytoplasmic staining or P anka, which is perinnuclear staining. So when you're looking at kind of these antibodies in conjunction, the C aa, the antibodies should be directed against that PR3 antibody. And the P anchor should be directed against the myeloperoxidase. And so those should be kind of in concert with each other. If they're not, then that may indicate that either there's a false positive or a different trigger. All right. So, what are we using this test for? What kind of conditions might we uh see with a positive anchca? The most common conditions that are associated with the ANA is ANA associated vascularities, and these are a group of small vessel vascularities that prime. Maly are one called Wegener's granulomatosis, and that was the old name. The new name is slightly longer. It's granulomatosis with polyangitis. There's another one called MPA or microscopic polyangitis, and then EGPA or eosinophilic granulomatosis with polyangitis previously also known as Scherg-Straus syndrome. All right. Let's change directions a little bit. Let's talk about an HLAB 27, and that's often measured in or checked in patients we suspect have a spondyloarthropathy. Um, what is this test? Yeah, so that's actually a different type of test than the ones that we've been talking about. The previous ones that we've been discussing are more autoantibody productions. This is actually a genetic test. So the HLA stands for human leukocyte antigen. And so, when you're looking at this, this is something that's on a white blood cell and it'll present cells to T cells for higher level activity. But really it's encoded in this area called the major histocompatibility complex or MHC which is located on chromosome 6. So this is a test where as opposed to inflammatory markers where you can watch them over time in some patients or things like rheumatoid factor or CCP or it's antibodies, this is a genetic. if it's been checked once, you don't really need to check it again. You just need to find the report because it's not going to change with time. So you're born with this. Correct. From birth through death. Yep, should not modify. And what conditions are associated with the positive HLAB 27? So the most common condition that's associated with a positive HLAB27 in the context of what we see in rheumatology is an inflammatory spondyloarthropathy or commonly ankylosing spondylitis. But uh again, it's important to keep in mind that while 90% of patients with ankylosing spondylitis will possibly have an HLAB27 genetic marker, and it predisposes to having this about 8% of the general population carries this genetic marker within the Caucasian population, and that varies from population to population as well. But in the right clinical circumstances, so if somebody is presenting with Chronic back pain or inflammatory back pain, those are circumstances where this test can increase your pre-test probability of having a diagnosis of uh an inflammatory spondyloarthropathy. OK. But by itself, it does not rule in or rule out that condition. So what I'm basically seeing from all of these tests is, these tests are helpful, but you can have the condition and still have a negative test. And you can have a positive test but not have the condition, correct? Yeah, I think that summarizes all of rheumatology, right? So you really have to use your brain, you really do, because like you mentioned, you either can have the positive marker but not have the disease. You can have the disease and sometimes not have the marker, and then if things line up perfectly, you have the disease and you have the marker, right? But that's why I think a common theme for this is that when checking these labs, if you are firing off ANA, rheumatoid factors, CCP, B27, etc. Since all of these have a false positive rate or they're seen within the general population, many people can have these positive and then you really have to go back and say, are these validated based on the clinical symptommatology? And really that's why none of these, none of these markers or labs in and of themselves in isolation guarantee the disease. They all are clinically diagnosed, so we have to have the appropriate clinical symptommatology. In the context of an accurate history that fits within the spectrum of that disease, and then ideally also have Supportive labs and antibodies. And so I think that's a running theme throughout this, but since there's a lot of tests and labs that are done for varying circumstances, like Ashma mentioned, this is one of the things that keeps rheumatology in business is anyone who has an abnormal lab within the spectrum, we have to kind of dig into it and try to figure it out. OK. Absolutely, I completely concur with uh Matthew on that one. And one thing that I tell my residents and fellows is that don't go fishing. If you fish, you will find something, and then you need to know what to do with that lab marker. So if, you know, if your pre-test probability is not pretty high, don't go there. Yeah, it's and the bigger the net you use, the more you're going to catch. So, uh, be very, be very careful. All right, last test, creatin kinase. Creatine kinase is essentially an enzyme that's found in skeletal muscle. Now, there's different isoforms of this enzyme. In the highest proportion, it's in skeletal muscle and the isosome of MM, but you can also see this in MB, so CKMB is in the heart tissue. And then there's also actually a creten kinase at BB that's in the brain. But when we're testing for this, the predominant one. That overshadows all of them is the skeletal muscle component for creatine kinase. When there's irritation, injury, trauma, overuse, anything that can lead to irritation and leakage from the muscle, this enzyme can be found in the bloodstream. And so, when you detect it, then you have to try to understand what of those factors might be contributing to its availability or identification within the blood. Mhm. So what conditions are associated with an elevated creatininese? So there are numerous conditions associated with an elevated CK and the large majority I would say are non-rheumatic, but when we think about rheumatic conditions, we think about inflammatory myopathies, particularly dermatomyositis, polymyositis, inclusion body myositis, but myositis can also be a component of lupus, mixed connective tissue disease, systemic sclerosis. It can be seen in a group of Conditions called anti-synthetic syndromes that can be associated with institial lung disease, renas, and inflammatory arthritis as well. But then important to keep in mind, you know, muscle injury, trauma, things like rhabdomyolysis, infectious myositis, drugs like statin can cause a myopathy as well. There can be endocrine causes of elevated CK like in hypothyroidism. So, again, that clinical history exam becomes very important to kinda understand what sort of workup that you pursue for an elevated CK. Yeah. Well, Ashima Matthew, you certainly have job security because I think you're the only ones who really understand all of these tests. There are quite a few. Can you summarize our discussion on rheumatologic tests, maybe with 2 or 3 key points? Yeah, I think one of the key points we've already mentioned to some degree, it's really trying to understand the disease and how they present and using what the patient is telling you from symptoms or history to raise the suspicion for whether you think a rheumatic disease is present before initiating an investigation of what labs to do. Now, unfortunately, Also within rheumatology, a lot of the symptoms can be vague and non-specific. So we recognize that people are gonna order these tests and they may be saying, well, we just don't understand why patients have these symptoms. And so part of it is too, if you don't know if you should or if there's symptoms where they're kind of funny or you're not exactly sure what could be there. Then sometimes seeking a rheumatologic consultation in advance of fishing for a lot of these things. Now, sometimes that can be difficult because rheumatologists are, are hard to find because we need to have more in this country. But I, I think it's really trying to say you really need to have a good suspicion for a rheumatic or inflammatory process before launching down this path. And I will just add to that. Just given our ANA test is the most popular and uh gets older the most, you know, ANA is not equivalent to lupus and that's a very important point to educate our trainees on as well. It's important to make sure they understand when to get an ANA and that would be typically symptoms concerning for lupus like inflammatory. Arthritis or photosensitive skin rashes like the mailer or discoid rash, uh, patrioscarring, alopecia, if they have cytopenia, if they have pseudositis, if they have unexplained thrombotic issues like DVTs and PE's in a younger population within the reproductive age group, particularly females, or if they suspect Sjogren's syndrome with significant dry eyes or dry mouth that are unexplained. By other factors such as medications or in patients with systemic sclerosis who present with RAS for the first time after the age of 40 in particular, having digital ulcers, skin sclerosis, interstitial lung disease, amongst others. So those are some of the key features that should make you think about a possible systemic rheumatic disease where an ANA will be high yield, but in many circumstances like Panels for fibromyalgia or chronic back pain and ANA may not be of the best use. We've been discussing the numerous rheumatologic tests we have available with rheumatologist Doctor Ashman McCall and Doctor Matthew Cost. both from the Mayo Clinic. Ahima, Matthew, thank you so much for sharing your expertise with us today. Thank you for having us. Yes, thank you. You can now listen to over 100 different medical topics developed for primary care providers on Mayo Clinic Talks podcasts. Find them at c.mailo.edu or your favorite podcasting app. If you've enjoyed Mayo Clinic Talks podcasts, please follow us. Stay healthy and see you next week.
