May 04, 2016

Quality Control in Veterinary Diagnostic Testing

A review recently published in The Veterinary Journal discusses ways to minimize errors in veterinary diagnostic testing, both with tests run in-house and those sent to diagnostic laboratories.
By Laurie Anne Walden, DVM, ELS
A review recently published in The Veterinary Journal discusses ways to minimize errors in veterinary diagnostic testing, both with tests run in-house and those sent to diagnostic laboratories.
 
Melinda Camus, DVM, DACVP, writes that quality control is an emerging subspecialty of veterinary clinical pathology. Because of the increasing availability of point-of-care analyzers, standard laboratory tests are often performed in-house. Quality control is necessary to ensure accurate results. “The approach to quality control in an in-clinic setting initially can be daunting,” she writes. “However, by breaking the testing process into three basic phases (preanalytic, analytic, postanalytic), sources for error can be identified and, hopefully, prevented.”
 

Preanalytic phase 

The preanalytic phase occurs before a diagnostic test is run. Sources of error during this phase include the following:
  • Mislabeling or not labeling a specimen tube
  • Allowing blood to clot before running a complete blood count
  • Accidentally introducing EDTA into a blood sample for chemistry analysis (by inserting a needle into an anticoagulant tube and then into a serum tube)
  • Improper preparation of samples for specialized testing  
A dog described in the review died because of EDTA contamination of a blood sample. EDTA chelates calcium and magnesium, causing the reported levels to be falsely low. The dog had a serum calcium reading of less than 4.0 mg/dL (reference range, 8.9-11.4 mg/dL). The attending veterinarian administered intravenous calcium gluconate, which caused the patient to develop a cardiac arrhythmia and die. Potassium EDTA also increases the reported level of potassium; the dog’s serum potassium level was greater than 7.0 mEq/L (reference range, 3.6-5.5 mEq/L).
 
Flow cytometry, polymerase chain reaction for antigen receptor rearrangement, and immunocytochemistry are specialized diagnostic modalities used to identify cell populations (usually neoplastic cells). These modalities require specific sample preparation protocols, which are described in detail in the review.
 

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