The reading of the blood pH value of 6.4 indicates a health issue because of the pH value. It is because the concentrations of H+ ions in the body becomes 10 times more than the usual level in the body.
The pH of the blood becomes less than 7.35 due to enhanced production of hydrogen ions by the body or the incapability of the body to produce bicarbonate ions in the kidney, the condition is known as metabolic acidosis that eventually results in acidemia.