Lab reference
LDH
What the research found.
One review pooled 27 groups of patients with anti-MDA5 dermatomyositis, 2,579 people in all. Lactate dehydrogenase came out among the best blood markers for telling apart who got a fast-moving lung problem and who didn't. The difference between the group averages was 75.94, with the true value somewhere from 64.20 to 87.67.
That review tested two other markers of damaged tissue, called AST and ALT, and both did far worse at telling the two groups apart. Their differences between group averages were 24.35 and 26.20. Lactate dehydrogenase came in at 75.94, well ahead of both, which is why it's the marker worth looking at here.
Liu and colleagues, Rheumatology, 2026
Two other things predicted the lung problem in that review, alongside the enzymes. A fever raised the odds 3.16 times, and an antibody called anti-Ro-52 raised them 2.87 times. Those are odds rather than risk, and both were listed alongside the blood markers rather than as an afterthought behind them.
Liu and colleagues, Rheumatology, 2026
What the number means.
| Band | Value | What it means | Source |
|---|---|---|---|
| Anti-MDA5 dermatomyositis | Among the best blood markers | For telling apart who got a fast-moving lung problem. Across 27 groups and 2,579 patients. | Liu 2026 |
| Two other damage markers, one review | Differences of 24.35 and 26.20 | AST and ALT told the two groups apart far worse than this marker did. | Liu 2026 |
| A fever, as a predictor | Raised the odds 3.16 times | Listed alongside the blood markers rather than behind them. | Liu 2026 |
| Anti-Ro-52 present | Raised the odds 2.87 times | An antibody that predicted the lung problem too, in those patients. | Liu 2026 |
| A range to aim at | None here | It's a risk marker inside one illness. It isn't a number to follow. | No source, because none exists |
A reference range is not a target. Where a range on this page differs from the one your laboratory prints, the difference is explained above and sourced below. Where no trial has tested a target, this page says so rather than offering one.
What the test measures
Lactate dehydrogenase is an enzyme that lives inside your cells, where it helps turn lactate into pyruvate as part of ordinary energy work. It sits in almost every tissue in the body, and it leaks into the blood when cells get damaged and their contents escape. So the blood level is a measure of cell damage somewhere in you.
Being everywhere is the whole problem with this test. A raised lactate dehydrogenase tells you cells somewhere have been hurt without telling you where, because muscle releases it, and so do liver, blood cells, lung, and tumor tissue. Even a difficult blood draw that damages red cells in the tube will push the measured value up, which is worth knowing before you read too much into one result.
Why it isn't a diagnostic test in rheumatology
Lactate dehydrogenase appears in no rheumatic rulebook, and not one set of classification criteria uses it. That isn't an oversight by the people who wrote them, because the enzyme is too general to tell one illness from another and those rulebooks are built from features that can. So its absence tells you something in itself.
Doctors measure it often anyway, above all in myositis, where muscle damage raises it and the level roughly tracks how much damage there is. In that setting it works as one piece among several rather than as a test with a cut-off of its own. Creatine kinase is the muscle enzyme followed more often, and the two usually move together.
Here is what that means if you're reading your own results. A raised value needs reading against everything else, which makes it a prompt to look further rather than a finding on its own. Usually what else is abnormal settles where the enzyme came from.
The one setting where it counts
Anti-MDA5 dermatomyositis is the exception, and it's an important one. That form comes with lung scarring that can get worse fast, moving in weeks rather than months, and it kills. So working out which patients are at risk changes how urgently they get treated, which makes any marker that helps with that clinically valuable.
A 2026 review pooled 27 groups of patients, 2,579 people in all, with anti-MDA5 dermatomyositis, and looked for what predicted the fast-moving lung problem. Lactate dehydrogenase came out among the best blood markers for telling those patients apart. The difference between group averages was 75.94, with the true value somewhere from 64.20 to 87.67, comfortably clear of zero, and the P value came in below 0.00001.
The comparison with other damage markers is what makes that interesting. AST came in at a difference of 24.35 and ALT at 26.20, both real and both far weaker. Two other things predicted the lung problem in that review, where a fever raised the odds 3.16 times and an antibody called anti-Ro-52 raised them 2.87 times. So the enzyme that sorts nothing across rheumatic disease in general sorts well inside this one high-risk group.
Why that finding still gives you no number
The review reports a difference between group averages, which is a statement about groups. The patients who went on to get the fast-moving lung problem had higher lactate dehydrogenase on average than the ones who didn't. That's genuinely useful for a doctor deciding how closely to watch somebody, and it isn't a cut-off you can hold one person's result against.
Only one cut-off exists anywhere in this research, at 459 units per liter, and it came from a single group of patients, with nobody having tested it anywhere else. A cut-off nobody has tested outside the data it came from is a hypothesis rather than a decision rule. Printing it here risks making it look official, and leaving it out risks somebody finding it elsewhere with no caveat attached, so it appears here with the caveat attached and it isn't a number to act on.
What to do with a raised result
Say you have myositis and a raised lactate dehydrogenase. That's expected rather than alarming on its own, because active muscle inflammation releases it. The level belongs in a wider look covering your antibodies, your muscle strength, the trend in your creatine kinase, and above all your breathing, and creatine kinase is the muscle enzyme followed more routinely, with the two usually moving together.
Breathing is the part worth being blunt about. New or worsening shortness of breath needs prompt medical care, and so does a new cough, or finding you can't do as much as you could. That holds for anybody with dermatomyositis whatever a blood test shows, because lung trouble in this illness can move faster than an outpatient appointment schedule, so the symptoms lead here the way they do in giant cell arteritis.
Outside myositis, a raised lactate dehydrogenase on its own usually means something else is going on, and the rest of your results will point at what. Liver disease, red cells breaking down, and recent tissue injury are the common explanations. So take the result to a doctor rather than reading it alone, because the list of possibilities is long and cutting it down needs your whole clinical picture.
Questions patients ask.
What does a raised LDH mean?
It means cells somewhere have been damaged, and it doesn't say where. Lactate dehydrogenase lives in almost every tissue in the body, so it rises with muscle injury, with liver disease, with red cells breaking down, with lung injury, and with some cancers. Even a difficult blood draw can raise it, and that breadth is why the number alone tells you so little, making it a signal to look further rather than a finding.
Is LDH used to diagnose any rheumatic disease?
No, and that's worth being clear about, because lactate dehydrogenase appears in no rheumatic rulebook at all. Doctors do measure it often, above all in myositis, where muscle damage raises it and it works as one piece of a bigger picture. It isn't a test that makes a diagnosis, and nobody has set a cut-off for it that means anything on its own.
Why is it important in MDA5 dermatomyositis?
Because that illness can scar the lungs within weeks, so working out who is at risk changes treatment urgently. One review pooled 27 groups of patients, 2,579 people in all, and lactate dehydrogenase came out among the best blood markers for telling apart who got the fast-moving lung problem. The difference between the group averages was 75.94, which put it well ahead of AST and ALT, so this is the one setting where the marker counts for something real.
Is there a level that predicts lung involvement?
None you can use, and that distinction counts. The review reports a difference between group averages, meaning the patients who got the fast-moving lung problem had higher levels on average than the ones who didn't, which isn't a cut-off you can hold one person's result against. One cut-off does exist, at 459 units per liter, though it came from a single group of patients and nobody has tested it elsewhere, so don't use it to decide anything.
My LDH is high and I have myositis. Should I be worried?
It's worth raising with your rheumatologist rather than reading alone. Lactate dehydrogenase rises whenever muscle gets damaged, so a raised level in active myositis is expected and isn't alarming on its own. What the MDA5 research shows is that the level belongs in a wider look covering your antibodies, your breathing, and your lung scans. One thing needs prompt care whatever the number says, which is new or worsening shortness of breath.
Should I track my LDH over time?
There's no evidence about what a change in it should make you do, so tracking it yourself tends to bring worry rather than information. It also moves for reasons that have nothing to do with your disease, since exercise moves it and so does how the sample was handled. Whether it's worth rechecking is a fair question for whoever ordered it. Their answer will depend on what they're watching for.
References.
- Liu T; Ji X; Wei Y et al. Predictors of rapidly progressive interstitial lung disease in anti-MDA5 dermatomyositis: a meta-analysis. Rheumatology (Oxford, England). 2026;65. 10.1093/rheumatology/keag311Systematic review and meta-analysis of 27 cohorts
This page gathers the published research on this subject into one place. The studies behind it were published between 1989 and 2026, and every figure links to the paper it came from. Those studies were peer reviewed. This summary of them was not. Dr. Sarah Luebker is reviewing these pages one at a time and has not reached this one yet, so it carries no medical review date and nothing here is her opinion or her advice to you. Each page gets updated as she reaches it. It is here in the meantime because the science is worth having in one organized place that is easy to find and easy to read. Talk to your own clinician before acting on any of it.