Empeiria

Lactate dehydrogenase

Also known as LDH, lactate dehydrogenase

enzyme activity · no single molecular formula

LOINC 14804-9 code verified serum U/L

What this substance is

Reported in U/L, units of catalytic activity. LDH interconverts lactate and pyruvate, using NAD+ and NADH; the test times that reaction.
What it catalyses

EC 1.1.1.27

(S)-lactate + NAD+ = pyruvate + NADH + H+

UniProt P00338

The reaction the test times
(S)-lactic acid
+
NAD+
→
pyruvic acid
+
NADH

Each molecule is drawn from ChEBI's curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Atom diagrams are checked against the NIST Atomic Spectra Database.

3D model

Predicted structure of one LDH-A chain (AlphaFold). The working enzyme is four chains. Predicted by AlphaFold (model v6, average confidence 96 of 100); its sequence matches UniProt exactly. Colour is AlphaFold's own confidence for each part: dark blue very high (above 90), light blue confident (70-90), yellow low (50-70), orange very low (below 50). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. You do not need to do anything special to get ready. Hard exercise and some medicines, such as aspirin, can raise the result. Red blood cells that break open while the sample is taken can also make it read high.

LDH is measured on a venous blood sample with no special preparation. Other fluids (CSF by lumbar puncture, pleural fluid by thoracentesis, peritoneal fluid by paracentesis) may be tested when indicated. Haemolysis during collection or testing, intense exercise and some drugs including aspirin can raise LDH; an LDH isoenzyme test separates five forms when tissue origin matters.

Where: laboratory

Source: Lactate Dehydrogenase (LDH) Test -- MedlinePlus Medical Tests, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

kinetic enzyme

IFCC-based kinetic UV (lactate to pyruvate)

LDH is a helper protein found in many body tissues. The machine gives it a sugar breakdown product to work on and watches a chemical build up that soaks up ultraviolet light. The faster it builds up, the more LDH there is.

LDH oxidises L-lactate to pyruvate with NAD+ as cofactor; the initial rate of NADH formation, read as rising absorbance at 340 nm, is proportional to catalytic LDH activity (formulation derived from the IFCC recommendation).

  • Read by: Rate of NADH absorbance increase at 340 nm

What can throw it off

  • Haemolysis (any amount; red cells release LDH)
  • IgM gammopathy (rare)
Why labs disagree: LDH is an enzyme-activity test, so the number depends on the reaction conditions each method uses. In an eight-platform comparison on serum from healthy volunteers, LD was flagged as method-dependent, with enough bias from method differences that at least two method-specific reference intervals would be required.

Sources: Koerbin G et al. Bias Assessment of General Chemistry Analytes using Commutable Samples. Clin Biochem Rev 2014;35:203-211 (PMC4310060); NHANES 2017-2018 Laboratory Procedure Manual, Lactate Dehydrogenase (LDH), CDC/NCHS cited · not yet checked by a person

What it reports on

Associated symptoms

Conditions this marker features in

When high
  • high Anaemia from red cells breaking down too fast · supportive
    A marker of red cells breaking down inside blood vessels. A marked rise is typical of that kind of haemolysis. It can also be raised for other reasons, such as low B12.
  • high Low vitamin B12 · supportive
    Raised because red-cell precursors are destroyed inside the bone marrow; it can be very high.