Lactate Dehydrogenase (LDH) Blood Test

LDH helps cells make energy. It is found throughout the body, including red blood cells, liver and muscle. A total LDH test combines these contributions. The same raised number can therefore appear in very different clinical situations.^{See reference 1}

Red blood cells contain much more LDH than serum. If they break open after collection, LDH can leak into the sample. Mayo rejects grossly haemolysed samples and lists collection and transport as possible sources of interference.^{See reference 2}

A report comment about haemolysis is therefore a prompt to check specimen quality. It does not, on its own, establish haemolytic anaemia inside the body. The laboratory and clinician can decide whether the number is usable or whether recollection is needed.^{See reference 2}

Two explanations can look similar on a graph: LDH may be released from tissues before the blood draw, or from cells damaged in the tube afterwards. The number alone cannot distinguish the two. Keep laboratory comments with the result.

Mayo lists 122–222 U/L for its serum LDH assay in adults aged 18 and over, with different intervals for younger ages. Use the interval that belongs to your own specimen, age and laboratory.^{See reference 2,See reference 4}

In an invented report, 240 U/L against an upper limit of 200 U/L is 1.2 times the limit. Against an upper limit of 250 U/L, the same number is below that limit. This arithmetic illustrates why a detached number loses context; it does not compare the accuracy of two assays.^{See reference 4}

LDH can be used in monitoring some cancers, alongside other evidence. Mayo specifically notes that LDH elevations are too variable to diagnose cancer. A monitoring role after diagnosis does not make a test a reliable cancer screen.^{See reference 2}

Similarly, LDH does not act as a liver-only marker or identify one damaged organ. Clinicians choose follow-up according to the reason for testing, symptoms and other results, rather than working through a list of diseases suggested by one flag.^{See reference 1}

Low LDH is uncommon and usually is not considered a health problem. MedlinePlus notes possible effects from large amounts of vitamins C or E and rare inherited explanations. A low result is not a reason to add or remove supplements without reviewing the context.^{See reference 1}