LDH value after a heavy training week

This test measures the total amount of LDH in the blood. The enzyme exists in five forms, the isoenzymes LDH-1 through LDH-5. LDH-4 and LDH-5 sit mainly in skeletal muscle. Those two are exactly what muscle work releases.

The enzyme drives the conversion of lactate into pyruvate. That is the same reaction your muscles use during intense effort. Even so, the test measures neither lactate nor lactic acid. When LDH is measured, it is the enzyme itself, not the fuel.

The routine assay adds all five forms together. So you get a single number back. That number does not separate muscle from liver or blood cell. LDH in the blood is therefore only usable beside a second marker.

For an athlete that second marker is almost always CK (creatine kinase). CK comes almost entirely from muscle tissue. If LDH and CK rise together, the source is muscle. If CK stays normal while LDH rises, the source lies elsewhere.

AST also rises with muscle damage. That can make a liver panel misleading.

This is how the three values behave after a hard session.

A raised LDH in a trained athlete is usually not an alarm. It is often simply the bill for your last hard session. Eccentric loading does this most strongly. Think heavy negatives, downhill running, or a first session back after a break.

The rise is also larger the more unfamiliar the stimulus is. A seasoned lifter running their usual programme sees little movement. That same lifter after a new exercise sees raised values that persist for days.

That makes LDH of limited use as a performance marker. The value follows your load, but with a lag and with plenty of noise. It does not tell you whether you are overtrained. Mostly it tells you that you trained hard recently, which you already knew.

Where the value does earn its place is in ruling things out. Draw blood after a week of rest. If LDH is still raised, training is not the explanation. That is when the question gets interesting.

The first alternative explanation is the tube itself. In haemolysis, red cells break apart after the draw rather than inside your body. When red blood cells rupture that way, the lab measures LDH that was never there.

A second cause is anaemia. It is more common in endurance athletes than people assume. A third is a recent viral infection, which had already interrupted your training anyway.

One more thing often surprises athletes. A trained athlete usually carries a slightly higher baseline than someone who does not train. That comes from greater muscle mass and near-continuous low-level muscle turnover.

Your personal normal may therefore sit higher in the range. That is not an abnormality and needs no action.

It does explain why your own earlier result is a better yardstick than the laboratory's upper limit. So measure once during a quiet period and keep that number. At every later measurement you then compare against your own baseline. A shift relative to yourself says more than a position within a population range.

On cancer we can be brief. LDH is not a screening test and does not detect cancer. Doctors use the value only to follow a disease that has already been diagnosed.

With this marker, timing determines almost everything. Draw blood at least 72 hours after your last hard session. For a genuinely clean baseline, allow a full week without unaccustomed load.

If you do not, you are measuring your training rather than your health. That is the most common mistake in blood work among athletes. Take a panel drawn on Monday, after a heavy Saturday. It shows raised liver and muscle values. None of them reflects a problem.

Draw fasted in the morning and drink enough water the evening before. Good hydration makes venepuncture easier, and a smooth draw reduces the chance of haemolysis.

If you repeat the measurement, do it under the same conditions. Same time of day, same recovery window, same laboratory. Only then is the difference between two measurements meaningful.

Never order LDH on its own. Pair it with CK for the muscle question. Add haptoglobin when red cell breakdown comes into view. State at the draw when you last trained intensely.

Plan a follow-up measurement deliberately rather than impulsively. Repeating within a week of a raised result says little. The enzyme is still falling at that point. Two to three weeks later, after a quiet period, gives a far more usable picture.

If you keep a training log, record the date of every blood draw in it too. With an abnormal result you then see immediately which week preceded it. That single detail answers most questions before a second test is needed.