Is routine pre-anaesthetic haematological and biochemical screening justified in dogs?

To determine if routine haematological and biochemical screening is of benefit in dogs requiring anaesthesia and to establish the most useful tests for pre-anaesthetic risk assessment.

One thousand five hundred and thirty-seven client-owned dogs undergoing surgery at the University of Leipzig between January 2003 and April 2004.

After obtaining a standardized history and a physical examination, all dogs requiring anaesthesia were assigned to an ASA physical status group, their needs for pre-anaesthetic therapy determined and an anaesthetic protocol proposed. Haematological (haematocrit, red blood cell count, white blood cell count, platelet count and haemoglobin concentration) and serum biochemistry tests (plasma urea, creatinine, glucose, total protein, sodium and potassium concentration; serum alanine aminotransferase, alkaline phosphatase and lipase activity) were then performed in all animals. The results of these were then used to: 1) re-define each dog's ASA physical status; 2) determine any altered requirement for pre-anaesthetic therapy; 3) re-determine the suitability of the dog to undergo surgery; and 4) re-examine the suitability of the original proposed anaesthetic protocol.

The history and clinical examination in 1293 out of 1537 dogs (84.1%) revealed that haematological and biochemical tests would have been considered unnecessary under normal conditions. Of these, 63.9% were categorized as ASA 1, 28.5% as ASA 2, and 7.6% at higher risk. In some dogs, screening tests showed abnormal results: 16.7% of 1293 dogs had abnormal plasma urea levels, with 5.9% of values above the reference range. However, only 104 dogs (8%) would have been re-categorized at a higher physical status category had the laboratory results been available. Additional screening data indicated that surgery would have been postponed in 10 dogs (0.8%) additional pre-anaesthetic therapy would have been provided in 19 animals (1.5%) and the anaesthetic protocol altered in two dogs (0.2%).

The changes revealed by pre-operative screening were usually of little clinical relevance and did not prompt major changes to the anaesthetic technique.

In dogs, pre-anaesthetic laboratory examination is unlikely to yield additional important information if no potential problems are identified in the history and on physical examination.