The Test

Test principle, storage, sample material, interference

Pyruvate kinase is a key enzyme in glucose metabolism and exists in various isoforms. In its active form, it consists of four equal subunits (tetramer). When a tumor develops, the tissue-specific isoenzymes are lost and expression of the M2 form of isoenzyme occurs. The amount of M2-PK increases and the isoenzyme that originally consisted of four subunits is split into a low-activity form consisting of two subunits (dimer). The dimeric form is generally detectable in large amounts in tumor cells.

The ScheBo^® • M2-PK Quick™ stool test is based on an immunochromatographic method. The M2-PK is detected by two specific monoclonal antibodies. M2-PK in the stool sample reacts with a monoclonal antibody bound to gold particles. This complex migrates along the membrane and reaches the test line to which a second monoclonal antibody against M2-PK is attached.

When the result is positive, the gold-labeled antibody-M2-PK complex binds to the test line and a pink color develops. When the result is negative, the sample does not contain any antibody-M2-PK complex that can bind to the test line and so no color becomes visible. Development of a pink control line guarantees that sample application and migration have taken place correctly and that the test was properly performed.

The test must be stored at +4°C to +27°C, and then brought to room temperature just prior to use if necessary.

After taking the stool sample, it can be stored at room temperature for no longer than 48 hours. Within these 48 hours, either the test must be performed or the sample frozen at -20°C for longer-term storage. The deep-frozen sample is stable for up to 1 year.

Very watery stools can lead to a false-negative result because of a dilution effect.

The ScheBo^® • M2-PK Quick™ stool test has 94% sensitivity and 96% specificity when compared with the M2-PK ELISA.