Serum lactate dehydrogenase activity ratios with different substrates

Area of Science:

• Biochemistry
• Clinical Chemistry
• Enzymology

Background:

• Lactate dehydrogenase (LDH) is an enzyme with multiple forms.
• Distinguishing between myocardial infarction and hepatocellular damage is clinically important.
• LDH isoenzyme analysis is a common diagnostic tool.

Purpose of the Study:

• To evaluate the diagnostic utility of LDH activity ratios using various substrates.
• To assess the effectiveness of different substrate combinations for differentiating myocardial infarction and hepatocellular damage.
• To investigate potential alterations in LDH activity ratios in cases of poisoning.

Main Methods:

• Assay of lactate dehydrogenase activity in sera from patients with myocardial infarction (n=89) and hepatocellular damage (n=55).
• Enzyme activity measured using pyruvate, alpha-oxobutyrate, hydroxypyruvate, and glyoxylate as substrates under optimal conditions.
• Activity also measured with lactate at varying pH values.
• Calculation and analysis of activity ratios between different substrate assays.

Main Results:

• Single ratio analysis showed varying differentiation accuracy, with glyoxylate/hydroxypyruvate and glyoxylate/alpha-oxobutyrate ratios exceeding 93% accuracy.
• Hydroxypyruvate/alpha-oxobutyrate ratio demonstrated minimal diagnostic value.
• Use of multiple ratios (up to seven assays) offered little improvement over single optimal ratios.
• An inverted hydroxypyruvate to pyruvate activity ratio was observed in a case of morphine poisoning.

Conclusions:

• Specific lactate dehydrogenase activity ratios, particularly those involving glyoxylate, are highly effective in differentiating myocardial infarction from hepatocellular damage.
• The diagnostic utility of LDH assays can be enhanced by strategic substrate selection.
• Alterations in LDH activity ratios may serve as indicators for specific toxicological conditions, such as morphine poisoning.