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Using the Diagnostic Pathfinder

The DP was designed to provide students with a meaningful and effective way to interact with and solve problems in clinical pathology, thereby improving their own diagnostic problem solving skills. In formal veterinary education it has generally served two purposed. First, some faculty have used the DP to model the diagnostic reasoning process in class and to present case solutions for classroom discussion. Second, students use the DP as a practice environment for homework case assignments. Students have also chosen to use non-assigned cases for test preparation and review. For a more detailed description of how the DP has been used in various settings, see the evaluation results section.

The Pathfinder 1) guides the students through the reasoning process in a stepwise manner and shows them the steps an expert faculty used to arrive at a diagnosis for each case. 2) reinforces good habits in data interpretation by requiring that all patient data be considered and explained, 3) provides a visual means for explicitly communicating diagnostic reasoning in the form of a diagnostic path, and 4) provides immediate expert feedback at the completion of the case by displaying the expert's diagnostic path, which will be explained in more detail below.

The Pathfinder is innovative in that it provides both a systematic approach to diagnostic reasoning and an explicit means for its communication. In contrast to automated expert systems, which provide students with a diagnosis, the Pathfinder helps students develop and refine their own evidence-based diagnostic reasoning skills.

Diagnostic Path: A diagnostic path communicates diagnostic reasoning in an outlined series of step-by-step cause and effect relationships between History observations (H), Data abnormalities (D) and Mechanisms (M). History observations are findings reported to the veterinarian by others, and laboratory data are the results of testing such as a complete blood count or a blood glucose level. Mechanisms are actions such as hemorrhage or the series of interactions by which insulin lowers blood glucose. Mechanisms are the essence of a diagnostic path because they represent an explanation of what caused each data abnormality, ultimately answering the question, “Why?” Without mechanisms, diagnostic reasoning is unsubstantiated and appears to be a list of rote memorized facts. Table 1 shows three stages representing an order by which a student might consider and explain abnormal data for a greatly simplified segment of a diagnostic path. Entries above and to the left “cause” or are “supported by” entries below and to the right. The progression from Stage 1 to Stage 3 represents the successive incorporation of additional data (D,H) and explanations (M). Stage 1 begins with the central concept of significant hemorrhage. Stage 2 incorporates supporting history observations and Stage 3 provides an explanation for the patient’s lethargy, which is a decreased supply of oxygen to the tissues, caused by the anemia.

Patient history/laboratory data: The owner reported that his dog is lethargic, and blood was found on the porch. Laboratory tests revealed anemia (decreased number of red blood cells) and hypoproteinemia (decreased amount of protein in the blood).

If placed in a narrative format, the diagnostic reasoning communicated in the Stage 3 diagnostic path would be the following:

This patient is the victim of trauma, which is supported by the owner’s report of blood loss. The blood loss is significant because the patient is anemic (from the loss of red blood cells), and has hypoproteinemia (from the loss of blood proteins). The anemia is causing a decreased delivery of oxygen to the tissues, which is supported by the owner’s report of lethargy.

The level of detail represented in a diagnostic path is determined by the instructional objectives of the course.