Lactate dehydrogenase (also called lactic acid dehydrogenase, or LDH) is an enzyme
found in almost all body tissues. It plays an important role in cellular respiration,
the process by which glucose (sugar) from food is converted into usable energy for
Although LDH is abundant in tissue cells, blood levels of the enzyme are normally
low. However, when tissues are damaged by injury or disease, they release more LDH
into the bloodstream. Conditions that can cause increased LDH in the blood include
liver disease, heart attack, anemia, muscle trauma, bone fractures, cancers, and infections
such as meningitis, encephalitis, and HIV.
Even though an LDH test is useful in diagnosing tissue damage, other tests are
usually necessary to pinpoint the location of the damage. One such test is called
the LDH isoenzymes test. LDH isoenzymes are five kinds of the LDH enzyme that are
found in specific concentrations in different organs and tissues. By measuring the
blood levels of these isoenzymes, doctors can get a better idea of the type, location,
and severity of the cellular damage.
Why It's Done
The LDH test is generally used to screen for tissue damage. This damage may be
acute (as in the case of a traumatic injury) or chronic (due to a long-term condition
such as liver disease or certain types of anemia). It also may be used to monitor
progressive conditions, such as muscular dystrophy and HIV.
No special preparations are needed for this test. On the day of the test, having
your child wear a T-shirt or short-sleeved shirt can make things easier for the technician
drawing the blood.
A health professional will usually draw the blood from a vein. For an infant, the
blood may be obtained by puncturing the heel with a small needle (lancet). If the
blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and
an elastic band (tourniquet) is placed around the upper arm to apply pressure and
cause the veins to swell with blood. A needle is inserted into a vein (usually in
the arm inside of the elbow or on the back of the hand) and blood is withdrawn and
collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected,
the needle is removed and the area is covered with cotton or a bandage to stop the
bleeding. Collecting the blood for the test will only take a few minutes.
What to Expect
Either method (heel or vein withdrawal) of collecting a sample of blood is only
temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may
be some mild bruising, which should go away in a day or so.
Getting the Results
The blood sample will be processed by a machine. The results are commonly available
within a day or two.
The LDH test is considered a safe procedure. However, as with many medical tests,
some problems can occur with having blood drawn, like:
fainting or feeling lightheaded
hematoma (blood accumulating under the skin causing a lump or bruise)
pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many children are afraid of
needles. Explaining the test in terms your child can understand might help ease some
of the fear.
Allow your child to ask the technician any questions he or she might have. Tell
your child to try to relax and stay still during the procedure, as tensing muscles
and moving can make it harder and more painful to draw blood. It also may help for
your child to look away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the LDH test, speak with your doctor.