LDH value too high: should you worry?

LDH stands for lactate dehydrogenase. On your report it is sometimes called LD; that is the same measurement. The protein helps cells get energy out of sugar, and because every cell does that, it is everywhere: in your muscles, heart, liver, kidneys, lungs and in your red blood cells. The lab measures the amount in your blood in units per litre (U/L).

That is why LDH is the least precise value on your report. A raised number says that cells have broken down somewhere, and nothing more. The lab cannot see whether that was your muscles, your red blood cells or something else. For that question a doctor looks at the other values on the same form.

The most important of those are CK, the protein that comes almost only from muscle, the complete blood count, which shows how your red blood cells are doing, and haptoglobin, which falls when red blood cells break down inside your body. With those three beside it, a doctor knows within a minute where a high LDH came from.

The normal range shifts with age: 118 to 251 U/L between 19 and 50, 128 to 274 between 51 and 65, 130 to 282 between 66 and 80. Those limits come from a Dutch study of more than seven million GP results.

Say your LDH is 320 and you feel fine. These are the explanations a GP works through, in order of likelihood.

One: the tube. Red blood cells are full of LDH, and if a few break during the draw, through an awkward draw, a thin needle or a tube left standing too long, their LDH is in your sample. The lab then often notes "haemolysis", and you see that AST and potassium are raised too while ALT is normal. That says nothing about your body. A new draw solves it.

Two: exercise. A hard workout damages muscle fibres, and those leak LDH, CK and AST into your blood, sometimes for a week. The less familiar the effort, the higher the number. That is part of recovery.

Three: an infection. Flu, a heavy cold or glandular fever raise LDH for weeks, even once you are feeling better. Four: anaemia from a shortage of vitamin B12 or folate, in which the production of red blood cells goes wrong; the blood count shows it. Five, and rare: red blood cells breaking down inside your body, with a low haptoglobin and a falling haemoglobin.

And cancer? Doctors use LDH to keep an eye on a cancer that has already been diagnosed, lymphoma for example, because fast-growing tumours give off a lot of this protein. LDH is not a test to find or rule out cancer. A mildly raised value in someone without symptoms does not point to cancer, and a normal value does not prove you are healthy. If you do have symptoms, swollen glands, night sweats, losing weight for no reason, then the LDH is beside the point: those symptoms themselves are the reason to see your GP.

You almost never need to request LDH separately; it is in most liver panels and general tests. If you get a raised result, the question is not "LDH again?" but "what is next to it?". CK, AST, ALT, potassium and a blood count together tell you where it came from.

Do not exercise hard in the two to three days before the draw. After something new or extreme, a first boot camp, a half marathon, the value can stay raised for a week, so wait longer then. Fasting is not needed for LDH.

Does your report mention "haemolysis", or are AST and potassium raised as well while ALT is normal? Then ask for a new draw before you make anything of it. If LDH is still raised on a clean draw and after a few quiet weeks, or if you have symptoms, discuss the whole result with your GP.