What is the significance of lactate dehydrogenase (LD) isoenzymes in newborns?

Significance of Lactate Dehydrogenase (LD) Isoenzymes in Newborns

Lactate dehydrogenase (LD) isoenzyme testing in newborns is most valuable as a biomarker for detecting cellular damage, particularly in hypoxic-ischemic events, and serves as a strong predictor of hypoxic-ischemic encephalopathy development in full-term asphyxiated newborns.

Clinical Significance of LD in Neonates

• LD is an enzyme released into the bloodstream when cell damage occurs, making it a useful marker for detecting tissue injury in newborns 1
• Elevated LD levels within the first 12 hours after birth can predict hypoxic-ischemic encephalopathy (HIE) with high sensitivity (100%) and specificity (97%) at a cut-off level of 1049 U/L 2
• LD measurements provide higher predictive value for identifying infants needing intensive care compared to lactate levels, as demonstrated by ROC curve analysis 3
• In full-term asphyxiated newborns, LD shows high sensitivity (90%) and specificity (71%) for predicting HIE development 4

LD Isoenzyme Patterns in Newborns

• Newborns have significantly different LD isoenzyme patterns compared to adults, with higher overall LD activity (approximately 4 times higher in newborn liver compared to adults) 5
• The isoenzyme distribution in newborns typically shows decreased LDH-H and increased LDH-M patterns 6
• In the liver of newborn piglets (animal model), LDH-3 and LDH-4 constitute the main portion of LD activity, with a shift toward the adult pattern (LDH-3 > LDH-2 > LDH-1 > LDH-4 > LDH-5) occurring within the first week of life 5
• Approximately 90% of LD is localized in the cytosolic compartment of the liver, regardless of age 5

Clinical Applications in Neonatal Care

• LD serves as an early marker of severe illness in NICU patients, with strong correlation between elevated plasma LD and poor clinical condition during the first week of life 3
• LD can be used alongside other diagnostic tests when evaluating newborns with suspected cellular damage from hypoxic events 1
• LD testing may help identify infants requiring intensive care measures, particularly in those born after 32 weeks gestation 3
• LD levels correlate with lactate levels (R = 0.496) but demonstrate superior predictive value for identifying infants needing intensive care 3

Diagnostic Considerations

• When evaluating newborns with suspected cellular damage, LD testing should be considered alongside other diagnostic measures rather than in isolation 7
• For infants presenting with brief resolved unexplained events (BRUE), routine metabolic testing including LD isoenzymes is not recommended unless there are specific clinical indications 7
• Serial measurements of LD within the first 72 hours of life provide better predictive value than single measurements 4
• The diagnostic utility of LD is higher in full-term asphyxiated newborns compared to premature infants 4

Limitations and Caveats

• LD elevation is not specific to any particular disease and must be interpreted in the clinical context 3
• In premature asphyxiated newborns, LD activities do not differ significantly between those who develop HIE/PIVH and those who don't, limiting its predictive value in this population 4
• The turnaround time for specialized testing may not coincide with the urgency of establishing a diagnosis for clinical decision-making 7
• False positives can occur due to hemolysis during sample collection, which artificially elevates LD levels 3