LD (Lactate Dehydrogenase) blood Biomarker Testing
LD measures a cell-damage enzyme in your blood to help explain inflammation or tissue injury, with easy ordering and Quest-based lab access via Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
LD (lactate dehydrogenase, sometimes reported as LDH) is an enzyme found in many tissues, including your muscles, liver, lungs, kidneys, and blood cells. When cells are stressed or damaged, LD can leak into the bloodstream and rise.
Because LD is not tied to just one organ, it is best thought of as a “signal” rather than a diagnosis. Your result becomes useful when it is interpreted alongside your symptoms, exam, and other labs.
If you are comparing lab options or trying to make sense of an unexpected abnormal value, this page walks you through what LD measures, what low and high results can mean, and what follow-up testing is commonly paired with it.
Do I need a LD test?
You might consider an LD test if you and your clinician are trying to explain a nonspecific pattern such as unexplained fatigue, persistent body aches, shortness of breath, fevers, or abnormal results on other labs that suggest inflammation or tissue injury.
LD is also commonly used as a “context” test when other markers are abnormal. For example, if your complete blood count (CBC) suggests anemia or hemolysis (red blood cell breakdown), or if liver enzymes are elevated, LD can help support or refine the next steps.
In some situations, LD is ordered to monitor known conditions where cell turnover or tissue injury can fluctuate over time. Trending LD can be more informative than a single value, especially when you are recovering from an illness, changing medications, or following a treatment plan.
Testing can support clinician-directed care, but it cannot tell you on its own what condition you have. If your LD is abnormal, the most helpful next move is usually adding targeted companion tests rather than repeating LD in isolation.
LD is measured from a blood sample in a CLIA-certified laboratory; results should be interpreted in clinical context and are not a standalone diagnosis.
Lab testing
Order an LD test (or add it to a broader panel) through Vitals Vault.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
Vitals Vault lets you order LD testing without needing a separate lab referral, and you can choose a single test or a broader panel if you want more context around an abnormal result.
After your results post, PocketMD can help you turn the number into a plan by explaining common causes of high or low LD, which companion labs are most relevant for your situation, and what retest timing usually makes sense.
If your goal is to track change over time, Vitals Vault makes it straightforward to reorder the same test so you can compare trends using the same lab network and consistent reporting.
- Order online and visit a local lab draw site
- PocketMD guidance for next-step questions to discuss with your clinician
- Easy retesting to follow trends over time
Key benefits of LD testing
- Adds a broad “tissue stress” signal when symptoms are real but the cause is unclear.
- Helps interpret possible hemolysis when paired with haptoglobin, bilirubin, and a CBC.
- Provides context for muscle or liver enzyme changes when combined with CK and AST/ALT.
- Can support monitoring of conditions associated with higher cell turnover when your clinician is tracking response over time.
- Helps distinguish a one-time lab artifact from a true pattern when you repeat it under better collection conditions.
- Works well as a companion marker in inflammatory or infectious workups when used with CRP/ESR and clinical findings.
- Makes trend-based follow-up easier when you keep testing and interpretation in one place with Vitals Vault and PocketMD.
What is LD?
LD (lactate dehydrogenase) is an enzyme your cells use to help convert lactate to pyruvate during energy production. Because it exists in many tissues, a blood LD level is a general indicator of cell injury, cell breakdown, or increased cell turnover.
LD is not specific to one organ. A high result can come from many different sources, including red blood cells, skeletal muscle, liver, lungs, or other tissues. That is why LD is usually interpreted alongside other tests that point to a specific system.
Some laboratories can measure LD “isoenzymes,” which are different forms of LD that are more concentrated in certain tissues. Isoenzyme testing is less commonly ordered today because modern panels (like cardiac troponin for heart injury) are more specific, but it can still be used in select cases.
One practical detail: LD is sensitive to sample handling. If red blood cells break during the blood draw or processing (in vitro hemolysis), LD can look falsely high even if nothing is wrong in your body.
What do my LD results mean?
Low LD levels
A low LD result is usually not a sign of disease and often does not require follow-up. In many labs, “low” simply reflects normal biological variation or differences in reference ranges. Rarely, very low values can be seen with certain genetic enzyme variants, but this is uncommon and typically shows up with a broader clinical story. If your LD is low but your other labs and symptoms do not suggest a problem, your clinician may treat it as a non-issue.
In-range (typical) LD levels
An in-range LD suggests there is no strong lab signal of widespread cell injury or rapid cell turnover at the time of the draw. This does not rule out a localized issue, early disease, or symptoms driven by non–tissue-damage causes. If you are evaluating fatigue, pain, or shortness of breath, normal LD is most helpful when you also review more specific markers (for example, CBC for anemia, CMP for liver/kidney function, and CK for muscle injury). Trends still matter, so a “normal” value can be reassuring if it is stable over time.
High LD levels
A high LD means more LD is present in your blood than expected, which often points to cell damage, inflammation, or increased breakdown of cells somewhere in the body. Common categories include hemolysis (red blood cell breakdown), liver or muscle injury, lung or kidney stress, and recovery after an acute illness. The degree of elevation and your other labs help narrow the cause; for example, high LD with low haptoglobin and a high reticulocyte count supports hemolysis. If LD is unexpectedly high, repeating the test and checking for sample hemolysis can be an important first step.
Factors that influence LD
LD can rise after strenuous exercise, muscle injury, or even a difficult blood draw that causes the sample to hemolyze. Many illnesses that create inflammation or tissue stress can increase LD, so timing matters—values may peak and then fall as you recover. Certain medications and medical conditions that affect the liver, muscles, or blood cells can shift LD as well. Because LD is nonspecific, the most useful interpretation usually comes from pairing it with targeted tests (CBC, CMP, CK, bilirubin, haptoglobin) and your clinical history.
What’s included
Frequently Asked Questions
What is the LD (LDH) blood test used for?
LD is used as a general marker of cell injury or increased cell turnover. It is often ordered to add context when other tests are abnormal (such as anemia/hemolysis, elevated liver enzymes, or muscle symptoms) or when symptoms are nonspecific and you need a broader picture.
Do I need to fast for an LD test?
Fasting is usually not required for LD by itself. If LD is being ordered with other tests (like a lipid panel or glucose/insulin testing), your clinician or the lab instructions may recommend fasting for the combined order.
What can cause a falsely high LDH result?
The most common reason is hemolysis of the blood sample, where red blood cells break during collection or processing. Recent intense exercise, muscle injury, or an acute illness can also raise LD, so the timing of your draw and your recent activity matter.
How do I know if high LD means hemolysis in my body?
LD alone cannot confirm hemolysis. A typical follow-up set includes a CBC, reticulocyte count, haptoglobin, indirect bilirubin, and sometimes a peripheral smear. The pattern across these tests is what helps your clinician determine whether red blood cells are breaking down in the bloodstream.
How soon should I retest LD if it is high?
Retest timing depends on the suspected cause. If sample hemolysis or a temporary trigger (like heavy exercise) is likely, a repeat in days to a couple of weeks may be reasonable. If LD is being used to monitor a known condition, your clinician may recommend a consistent interval (for example, every few weeks or months) so trends are comparable.
Is LDH the same as lactate?
No. LDH (LD) is an enzyme, while lactate is a metabolite that can rise with low oxygen states, intense exercise, or certain illnesses. They are related in metabolism, but they are different tests with different clinical uses.