Serum ALT profiles of a patient who acquired TTV infection. Biochemical evidence of liver disease in this patient during the study period was reflected by changes in the ALT level. The ALT levels (U/L, dotted line) were plotted against the date of determination; the upper reference limit for ALT was 40 U/L. Serum from this patient collected at the time of enrollment tested negative for TTV DNA by PCR. The serum samples collected at the conclusion of the 3-year follow-up tested positive for TTV DNA.