Pre-analytical problems in the measurement of tumor type pyruvate kinase (tumor M2-PK)

Tumor M2-PK is an isoform of the glycolytic enzyme pyruvate kinase. This isoform exists in an active tetrameric and less active dimeric form. The dimeric form is expressed by various tumor cells and can be measured in blood by a specific ELISA.

We included 500 healthy persons, 20 patients with an acute rheumatic disease (high CRP) and 30 patients with a nephropathy and proteinuria with more than 20 mg/dl. We measured Tumor M2-PK in each of these groups in different specimens of EDTA-plasma, serum, heparin-, citrate-, fluoride- and oxalate-plasma.

We found different concentrations of Tumor M2-PK in healthy persons depending on the kind of specimen. The normal range of Tumor M2-PK concentration was higher in the serum than in the plasma, with 35 U/l compared to 15 U/l. In haemolytic material we found concentrations up to 80 U/l in healthy persons. Lipaemic or icteric serum material showed a higher concentration of Tumor M2-PK as well. In patients with a triglyceride concentration higher than 300 mg/dl, the normal range for Tumor M2-PK was measured between 30-50 U/l. Similar results were found in patients with icteric serum. Patients with an active rheumatic disease and elevated CRP concentration showed a Tumor M2-PK concentration between 40-60 U/l. Patients with a nephropathy and proteinuria over 20 mg/dl had an elevated Tumor M2-PK concentration from 25-60 U/l.

We conclude that different materials seem to be suitable for the measurement of Tumor M2-PK concentration as long as attention is paid to different normal ranges. Haemolytic material should not be used as it offers false-positive results. Some diseases such as rheumatic disease, hyperlipidaemia and nephropathy have an influence on Tumor M2-PK concentration that should not be neglected.