LDH value too high: should you worry?

The test looks at all the LDH sitting in your blood. The enzyme comes in five forms, the isoenzymes LDH-1 through LDH-5. Each form sits in different tissues. Your heart and red blood cells mainly hold LDH-1, your liver and muscles mainly LDH-4 and LDH-5.

Inside the cell, the enzyme handles the conversion of lactate into pyruvate. That belongs to energy production and is not something you need to track.

What matters more is what the result can and cannot do. When LDH is measured, the lab adds all five forms into one number. That number cannot point to where the LDH came from. So LDH in the blood is never a diagnosis on its own.

Your doctor therefore always reads the value alongside the rest of your blood count. If your other values are normal and you feel well, a mildly raised LDH is rarely worth chasing.

Below are the causes in order of how often they occur. That order is exactly what most people miss when they start searching.

If you search for LDH, you reach cancer quickly. So that answer sits at the top here rather than the bottom.

LDH is not a cancer test. It is not screening, it does not detect cancer, and it does not rule cancer out. For a few cancers, such as lymphoma and testicular cancer, doctors do look at LDH. They do that in someone already diagnosed, to follow the course of the illness. They never use it to check whether someone has cancer.

So a normal LDH value is no proof that you are healthy. And raised values are no sign that something serious is going on. Do you feel well, with the rest of your result normal? Then a mildly raised number almost certainly reflects something very ordinary.

The most common cause is the tube itself. In haemolysis, red blood cells break apart inside the tube, so after the draw. When red blood cells rupture there, they release LDH that was never inside your body. The lab simply measures it along with the rest. They usually add a note, but not always.

Next comes exercise. A hard or unaccustomed session damages muscle fibres and lifts your LDH for a few days. CK is raised then too, and that combination makes it obvious.

After that comes a recent viral infection. Flu or glandular fever keeps your LDH raised for weeks.

Serious causes exist, but they almost always come with clear symptoms. Sudden breathlessness or chest pain are reasons to seek help immediately, not to wait for a blood value.

What happens if you take this result to your GP? The conversation usually starts with your symptoms rather than the number. Your doctor asks whether you have been ill recently, whether you trained hard, and how the draw went.

After that they look at the rest of your result. If your other values are normal, a repeat in a few weeks is often the entire plan. If more values are out of range, a targeted test for the suspected source follows.

What a doctor almost never does is order the same LDH test again straight away. That simply produces no new information.

You rarely order LDH on its own. It usually sits inside a panel you are having for another reason. A liver work-up or a general blood count, for example.

A standalone LDH measurement adds little. The number only gains meaning beside other values. Without that context you mostly end up worrying about a figure you cannot place.

If you want a result that holds up, watch two things. Do not exercise hard in the two to three days before the draw. Muscle work raises your value. And drink enough water the evening before. The draw then goes more easily and haemolysis is less likely.

Already have a raised result and no symptoms at all? Then repeating it after a few weeks is often the wisest step. Draw rested and well hydrated. Very often the second result is simply normal.

Do you have symptoms, such as persistent tiredness, pallor or fever? Then discuss the result with your GP rather than arranging a repeat yourself.