How to submit samples to the Diagnostic Lab
In most cases veterinarians initiate the submission of samples to veterinary diagnostic laboratories. In some cases producers, extension educators, or other ag professions may wish to send samples to expedite sample submission, or initiate herd problem solving. One of the first criteria that should be examined is the choosing of a laboratory. Many labs offer services, not all labs run sufficient controls or follow established standard operating procedures which ensure consistent and accurate results. It is important to choose a lab or inquire about a lab in question to see if it has met certification standards or has a documented history of consistent service that matches national or international criteria.
Before initiating sampling it is assumed that the local veterinary practitioner alone or along with a farm consultant team has visited the herd or has knowledge of existing herd or flock problems. While random survey samples have some relevancy in surveillance, such samples frequently are not sufficient for solving herd health problems. It is assumed that all diagnostic samples are sent to the lab with a tentative list of differentials and an adequate history. Both a differential list and a good history are critical to ensure that appropriate samples are submitted and that the subsequent diagnostic lab results can be interpreted and are meaningful to the ag producer.
Prior to taking any samples it is important to know what type of sample is needed for suspected diagnostic differentials, size of sample, type of containers, shipment requirements, and any special handling characteristics. In any case, the cardinal rule for laboratory submission is, ‘when in doubt always contact the lab in advance of sending samples’. Laboratories have established standard operating procedures (SOP’s) that ensure that they can accurately reproduce results for specific testing procedures. These SOP’s include how to best submit and receive samples. For diagnostic samples to have validity it is absolutely critical that sample handling and transport match the criteria as stipulated by the lab.
Secondly, some decision must be made as to the type of animals to test and the number of animals to test to ensure an accurate diagnosis. These decisions can be difficult in long standing problems or conversely in troublesome but infrequent cases. A good case definition is necessary. Just what are the clinical signs that designate a case? The better these can be defined the more likely that similar cases due to similar problems will be recognized and samples will be taken from these animals. Members of the herd that have non-specific problems but just happen to fall into the same timeframe should not be sampled. If this group of animals is a significant part of the sample pool they may produce confusing or misleading conclusions.
Number of animals to sample and number of repeat samples are always hard questions to answer. There are no absolute hard and fast rules. As many as (or more than) is convenient, or as many as economically possible, are good rules of thumb. The more sensitive and specific the test the more likely a few samples will confirm or deny a specific pathogen, metabolic condition, or toxin. Tests that have more variation in either sensitivity or specificity require greater numbers of samples or require the use of a different secondary test to confirm initial test conclusions. For questions about unusual herd diagnostic challenges it is wise to consult a veterinary expert who has additional training in epidemiology for guidance in selecting the most appropriate testing strategies.
For help with diagnostic laboratory submission decisions please refer to the Animal Diagnostic Laboratory
