Real-time PCR cycle threshold numbers (Cq values) for nine potential reference genes in 4 disease categories (n = 263) . Real-time PCR cycle threshold numbers (Cq values) are plotted for nine potential reference genes. Group A included 6 healthy dogs, group B 85 dogs within 24 hours after a surgical procedure, group C 107 dogs with miscellaneous internal diseases, and group D 65 dogs with hematologic diseases. Statistically significant differences between mean Cq of the disease categories are depicted.The boxes represent the two middle quartiles with medians. Whiskers delineate the range.