LDH value in anaemia and pregnancy

The assay adds up all the LDH in your blood. The enzyme occurs in five variants, the isoenzymes LDH-1 through LDH-5. LDH-1 and LDH-2 sit in high concentration inside red blood cells. That explains why red cell breakdown lifts the value so sharply.

The enzyme handles the conversion of lactate into pyruvate within the cell's energy metabolism. When LDH is measured, the laboratory adds all five variants together. So you see one number, with no indication of its source.

That is why LDH in the blood only becomes informative in company. For a woman with fatigue, it usually comes down to three partners.

Haemoglobin shows whether anaemia is genuinely present. Ferritin shows whether your iron stores are depleted, which heavy periods often cause. Haptoglobin shows whether red blood cells are being broken down faster than normal.

That third one is the key. Haptoglobin mops up released haemoglobin and is therefore consumed as soon as breakdown occurs. A high LDH with a low haptoglobin points to red cell breakdown. A high LDH with a normal haptoglobin points somewhere else entirely.

This table sets out the situations in which the question arises.

For women, the value of this test lies almost entirely in the anaemia question. Fatigue is a symptom with dozens of explanations. LDH singles out one group. That is where red blood cells disappear faster than they are made.

The most commonly missed example is a vitamin B12 or folate deficiency. In such a deficiency the bone marrow makes oversized, fragile red cells. Many of them are destroyed inside the marrow itself. When red blood cells rupture there, their LDH is released immediately. The result is a strikingly high LDH with a low haptoglobin. What you notice is tiredness and pallor.

That pattern matters because it is often mistaken for ordinary iron deficiency. Iron deficiency from heavy periods usually produces no raised LDH at all. So if you see raised values alongside anaemia, iron is probably not the whole story. That is when vitamin B12 and folate belong in the picture.

In pregnancy the value has a second role. LDH rises slightly in the third trimester, and that is normal. There is one pattern that is not. In the second half of pregnancy one combination matters most. That is a clearly raised LDH with low platelets and raised liver values. It needs same-day assessment. Particularly with headache, upper abdominal pain or nausea. Call your midwife or obstetrician then, rather than waiting for a scheduled check.

After delivery the picture changes again. In the first weeks LDH often sits temporarily higher. That comes from tissue repair and from blood loss around the birth. It usually normalises on its own within a few weeks.

Still markedly tired and pale during that period? Then have your haemoglobin and ferritin measured. Breastfeeding also raises your need for iron, vitamin B12 and folate. A deficiency therefore develops faster than many women expect.

Have you had heavy periods for years? Raise that explicitly with your GP, even if you have grown used to it. Prolonged blood loss is often experienced as normal. Meanwhile it steadily empties your iron stores.

One more note on cancer. LDH is not a screening test and can neither demonstrate nor exclude cancer. Doctors use the value only to follow a disease already diagnosed.

LDH is rarely requested on its own. The value usually arrives as part of a blood count or a liver panel.

There are, however, sensible moments. With persistent fatigue that sleep does not resolve. With pallor or breathlessness on mild exertion. With anaemia that does not respond to iron supplementation, which is the strongest reason to look further.

Your cycle does not meaningfully affect LDH. So unlike hormones, you do not need to schedule the draw for a particular cycle day. Do try to avoid the heaviest days of a heavy period. Your haemoglobin can read temporarily lower then.

Avoid heavy or unaccustomed exertion in the two to three days beforehand. Muscle work raises LDH even in people who do not train intensively. Drink enough water, because a smooth venepuncture reduces the chance of haemolysis.

Pregnant, with headache, upper abdominal pain or sudden swelling? Contact your midwife rather than arranging blood tests yourself.