What will excessive squeezing around a capillary puncture site cause?

Excessive squeezing will cause haemolysis of the sample, i.e., the rupture of red blood cells, thus releasing their content (Hb and electrolytes) into the plasma. Haemolysis will alter potassium, ionised calcium (ICa), phosphate and enzymes. If gross haemolysis occurs, all results may be affected, due to a dilution of the sample by dissolved haemoglobin.

Tissue fluid (resulting in increased potassium levels) may also contaminate the blood sample if you squeeze too hard.