Lactate Dehydrogenase Isoenzyme 1

🔬 What is LDH-1?

LDH-1 (H4 type) is one of the five isoenzymes of lactate dehydrogenase.
It is predominantly found in:

• Heart muscle (myocardium)

• Red blood cells (RBCs)

• Renal cortex

1️⃣ Myocardial Infarction (MI)

Historically important in diagnosis of acute MI.

Characteristic Finding: “LDH Flip”

Normally:

LDH-2 > LDH-1

After MI:

LDH-1 > LDH-2

This reversal is called the LDH flip.

Time Course in MI:

• Rises: 12–24 hours

• Peaks: 48–72 hours

• Returns to normal: 7–10 days

📌 Useful in late-presenting MI (when CK-MB already normal).
(Now replaced largely by troponin testing.)

2️⃣ Hemolytic Anemia

LDH-1 is markedly elevated because RBCs are rich in LDH-1.

Seen in:

• Hemolytic anemia

• Megaloblastic anemia

• Transfusion reactions

• Hemolytic disease of newborn

👉 LDH-1 elevation + high indirect bilirubin + low haptoglobin suggests hemolysis.

3️⃣ Renal Infarction

Since LDH-1 is present in kidney cortex, it may increase in:

• Renal infarction

• Severe renal injury