Lactate dehydrogenase activities in serum and plasma

Area of Science:

• Biochemistry
• Clinical Chemistry
• Laboratory Medicine

Background:

• Conflicting data exists regarding lactate dehydrogenase (LDH) activity in serum versus plasma.
• Platelets are known to contain high concentrations of LDH, potentially interfering with plasma assays.

Purpose of the Study:

• To investigate and resolve discrepancies in reported LDH activity between serum and plasma samples.
• To determine the impact of platelet contamination on LDH measurements in plasma.

Main Methods:

• Assayed LDH activity in serum, platelet-rich plasma, and platelet-poor plasma.
• Utilized two colorimetric endpoint methods and one ultraviolet kinetic procedure.
• Varied reaction mixture osmolality to assess platelet lysis effects.

Main Results:

• Platelet-poor plasma and serum showed comparable LDH activities across all methods.
• Platelet-rich plasma exhibited up to fourfold higher LDH activity when platelet lysis occurred.
• Consistent LDH levels were observed in platelet-rich plasma when platelet lysis was prevented (osmolality ~240 mOsm/kg).
• Lower LDH activity was noted in platelet-rich plasma at reduced osmolality (~120 mOsm).

Conclusions:

• Platelet lysis is a critical factor causing elevated LDH in plasma samples.
• Accurate LDH measurement in plasma requires preventing platelet lysis or using platelet-free plasma.
• Centrifugation of plasma (3000 x g, 15 min) is recommended to obtain platelet-free samples for reliable LDH determination.