Lactate Dehydrogenase

Lactate + NAD+ ⇌ Pyruvate + NADH + H+

What chemical reaction represents the process catalyzed by the enzyme lactate dehydrogenase (LD)?

Heart and liver

While it is widely distributed throughout the body, in which two organs is lactate dehydrogenase found in the highest concentrations?

H (heart) and M (muscle)

Structurally, each of the five major lactate dehydrogenase isoenzyme fractions is a tetramer composed of four subunits derived from which two polypeptide chains?

LD-2 > LD-1 > LD-3 > LD-4 > LD-5

What is the normal relative serum concentration pattern of lactate dehydrogenase fractions in a healthy individual?

LD-1 > LD-2

What clinical phenomenon is defined as the LD flipped pattern?

Myocardial infarction

The presence of an LD flipped pattern in a patient panel serves as a classic diagnostic finding for which condition?

LD-1

Which lactate dehydrogenase fraction is characterized as the most anodal fraction and is highly localized to the heart and RBCs?

LD-2

Which specific lactate dehydrogenase fraction normally exhibits the highest concentration in healthy human serum?

Myocardial infarction, hemolytic anemia, and megaloblastic anemia

Elevated levels of the LD-1 fraction are characteristically associated with which group of disorders?

Acute renal infarct or a hemolyzed specimen

An isolated elevation or artifact in the LD-2 fraction is commonly seen in which circumstances?

Lung, lymphocytes, spleen, and pancreas

Which tissue distribution is explicitly paired with the LD-3 isoenzyme fraction?

Pulmonary embolism, extensive pulmonary pneumonia, lymphocytosis, acute pancreatitis, and carcinoma

Elevations in the LD-3 fraction serve as a diagnostic indicator for which cluster of clinical conditions?

Liver

Which major organ is the primary tissue source for the LD-4 fraction?

Skeletal muscles

An isolated elevation in the LD-5 fraction is highly indicative of injury to which specific tissue?

Pernicious anemia and hemolytic disorders

In which clinical conditions or blood disorders are the absolute highest levels of total LDH typically observed?

Megaloblastic anemia

If a patient presents with pernicious anemia, what alternative terminology should the clinician look for regarding diagnostic classification?

Rises 12–24 hours after onset, peaks 48–72 hours, and remains elevated for 10 days

What is the characteristic temporal pattern of LDH elevation following an acute myocardial infarction (AMI)?

Wacker et al.

Which method for determining lactate dehydrogenase activity is defined as the forward reaction?

pH 8.3 to 8.9

What is the optimum pH range required for the Wacker et al. forward reaction method?

Wroblewski & La Due

Which method for determining lactate dehydrogenase activity is defined as the reverse reaction?

pH 7.1 to 7.4

What is the optimum pH range required for the Wroblewski & La Due reverse reaction method?

Rate of reaction is three times faster, allowing smaller sample volumes and shorter reaction times

What are the operational advantages of the Wroblewski & La Due reverse reaction method compared to the forward reaction?

More susceptible to substrate exhaustion and loss of linearity

What chemical limitation or risk is associated with the Wroblewski & La Due reverse reaction method?

Hemolysis releases massive amounts of intracellular LD from erythrocytes into the serum

Why must hemolysis be strictly avoided when collecting and processing blood samples for lactate dehydrogenase testing?

Do not freeze specimen

What specific storage constraint must be followed regarding LD specimen temperature control to prevent enzyme inactivation?

Serum

Which specimen type is designated as the sample of choice for LD determination because alternative anticoagulants like oxalate inhibit the enzyme?