Avoiding Errors in Veterinary Laboratory Diagnostics

Presented By: Dr. Nathan Heinrich, DVM, DACVP - Lab Error Quick Reference

PRE-ANALYTICAL Before sample analysis (60-82% of errors)
ANALYTICAL During sample analysis (6-15%)
POST-ANALYTICAL After analysis (9-20%)
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Courtesy Reference Document
This document has been extracted from lecture transcripts as a courtesy reference. We make no representations as to the accuracy of this information. All content should be verified against the individual practitioner's own medical training, clinical judgment, and current veterinary standards of care.
Error / Finding What It Looks Like Common Causes How to Detect / Prevent Supporting Quote from Lecture
False Hyperkalemia PRE-ANALYTICAL Elevated K+, low Na:K ratio; may mimic Addison's disease in young animals Thrombocytosis (platelets release K+ during clotting); EDTA contamination from purple-top tube; delayed serum separation Repeat on heparin plasma or i-STAT (whole blood); check platelet count; draw red-top before purple-top; separate serum promptly "If we don't get our serum quickly off of that red cell and platelet pellet, those platelets are going to release potassium into the sample."
EDTA Contamination PRE-ANALYTICAL Spurious hyperkalemia; may falsely decrease calcium; affects chemistry panel Drawing purple-top (EDTA) tube first, then red-top with residual EDTA on needle; human studies show 3-6% of hyperkalemic samples are EDTA contaminated Change blood draw order (red-top before purple-top when possible); use fresh needle for chemistry draw; consider human medicine draw order guidelines "If we drew our purple top first, and we got even a tiny bit of potassium EDTA left on the needle that got into our red top, that can cause spurious hyperkalemia."
False WBC Count (nRBC interference) ANALYTICAL Falsely elevated WBC count; bizarre differentials; nucleated RBCs counted as leukocytes Post-splenectomy patients; chemotherapy (marrow endothelial damage); heat stroke; seizures; any condition releasing nucleated RBCs Always make a blood smear; use nRBC correction formula: Corrected WBC = Observed WBC × [100 ÷ (nRBC + 100)]; inspect scatter plots for abnormal patterns "I do not trust automated analyzers to very accurately confirm or deny the presence of nucleated red blood cells... make sure to do smear reviews for patients that are on chemotherapy."
False Monocytosis (Blasts) ANALYTICAL Elevated monocyte count on automated differential; may mask leukemia Circulating blast cells (lymphoid or myeloid) are misidentified as monocytes by analyzers; blasts don't behave normally with regards to RNA content or enzyme expression ALWAYS question automated monocytosis >2,000; make blood film; look for large cells with immature chromatin and nucleoli; refer to clinical pathologist if suspicious "I never trust a monocytosis from an automated analyzer ever... especially anything over two [thousand], I don't trust it."
False Monocytosis (Gray Eosinophils) ANALYTICAL Monocytosis on automated count; actually eosinophilia when examined manually Gray eosinophils (granules don't stain pink) misidentified as monocytes; common in Greyhounds (53%), Whippets, Golden Retrievers; also reported in cats Recognize breed predisposition; blood smear shows cells with hyper-segmented nuclei but gray/vacuolated cytoplasm instead of typical monocyte appearance "Gray eosinophils... are most commonly seen in greyhounds and whippets, but we do also see them in golden retrievers... automated analyzers can misidentify these cells."
False Elevated GGT PRE-ANALYTICAL Markedly elevated GGT as sole abnormality; other liver enzymes normal RBC contamination of serum sample (red cells contain GGT); poor pipetting technique; serum separator gel failure Re-centrifuge sample and carefully remove serum; check for RBC pellet in stored serum; repeat on fresh sample if suspicious "Red cells do have a little bit of GGT in them... We were not careful to remove the red cells... we need to inspect our sample."
Wrong Species Selection PRE-ANALYTICAL Severe neutropenia with lymphocytosis; dramatic hematocrit discrepancy from PCV; bizarre differential Clinician submits wrong species; lab selects wrong species on analyzer; running dog blood as cat or vice versa Compare PCV to hematocrit (should be within 3%); look at cell morphology (dog eosinophils have round granules, cat eosinophils are rod-shaped); verify species with clinician "If you run dog as cat blood or cat as dog blood, the hematocrit will be completely erroneous. So your PCV is going to be very different from your hematocrit."
Urine Contamination PRE-ANALYTICAL Impossibly high values: BUN >500, creatinine >50, K+ >25; patient "shouldn't be alive" Blood added to tube that previously held urine; urine very high in potassium, creatinine, and BUN Use different colored tubes for urine (white-top) vs blood (red-top); smell sample if suspicious; results incompatible with life indicate contamination "They actually contaminated the sample with urine... A BUN of 500, a creatinine of 57, a potassium of 26.2. He really shouldn't even be alive."
Catheter Draw Contamination PRE-ANALYTICAL Unexpected hyperkalemia/hyperphosphatemia in supplemented patient; results inconsistent with i-STAT IV fluids not adequately cleared from catheter line before blood draw; patient on K+ or phosphorus supplementation Remove 3 mL blood before sampling from catheter; notify lab of catheter draws; compare to direct venipuncture if suspicious; avoid catheter draws when possible "That day 3 a.m. sample was drawn through a catheter... and fluids were not adequately cleared from the line prior to the blood draw."
False Thrombocytopenia (Catheter) PRE-ANALYTICAL Low platelet count with no clinical signs; no clots visible in tube; truly low estimate on smear Clot formation in/around catheter that doesn't transfer to EDTA tube; platelets consumed by clot before reaching tube Prefer direct venipuncture over catheter draws; correlate with clinical signs (bruising, petechiae); repeat with fresh direct draw if suspicious "Clots are going to form because that plastic is sitting in the vessel... clots in your syringe do not always transfer into the EDTA tube."
Heparin Flush Interference PRE-ANALYTICAL Coagulation test abnormalities; may affect other chemistry values Heparinized saline flush not cleared before blood draw; heparin contamination of sample Clear flush completely before drawing; remove adequate dead space volume; avoid catheter draws for coagulation testing "If you've done a heparinized saline flush, if you haven't removed that and that heparin gets in the sample, it can cause all kinds of problems."
Alcohol Contamination PRE-ANALYTICAL Complete hemolysis of sample; all RBCs lysed Excessive alcohol applied to skin; not allowed to dry; alcohol drawn into syringe with blood Allow alcohol to dry completely before venipuncture; don't over-saturate the area; if hemolysis occurs, redraw with proper technique "If you are dousing your patient with alcohol and not letting it dry, if you suck enough alcohol into the syringe, it's going to lyse all of the red cells."
Expired Tubes PRE-ANALYTICAL Unexpected results; possible bacterial contamination; seal failure Rubber stopper seal dries out and cracks over time; allows environmental contamination while sitting in drawer Check expiration dates on tubes regularly; rotate stock; discard expired tubes "A lot of our tubes have expiration dates... the seal on the rubber stopper starts to dry out and crack... we've had bacterial contamination in our tubes."
Pediatric Reference Interval Error POST-ANALYTICAL Flagged lymphocytosis in puppies/kittens; mild abnormalities that are actually age-appropriate Using adult reference intervals for pediatric patients; many labs don't have pediatric-specific ranges Know which values differ in young animals (lymphocytes higher, some proteins lower until 4-8 weeks); consult pediatric references; consider excitement response "We at our university only provide adult reference intervals. We do not provide pediatric reference intervals... this patient actually does not have a lymphocytosis [when using pediatric ranges]."
Whipworm Pseudo-Addison's POST-ANALYTICAL Hyperkalemia + hyponatremia mimicking Addison's; GI signs; young animal Whipworm infection causes electrolyte disturbances resembling hypoadrenocorticism through unclear mechanism; NOT an error but commonly misdiagnosed Consider age (5-month-old Addison's is unusual); do fecal exam; if suspicious, verify with ACTH stim test before treating for Addison's "Whipworm infection can cause pseudo-Addison disease. It can cause hyperkalemia and hyponatremia for reasons that have not been fully elucidated."
Lipemia/Icterus/Hemolysis (LIH) ANALYTICAL Flagged results; specific analytes affected; may cause false increases or decreases Lipemia (unfasted patient, disease); icterus (hyperbilirubinemia); hemolysis (rough blood draw, in vivo hemolysis) Fast patients when appropriate; note sample appearance; big labs will flag affected analytes; follow ASVCP quality assurance guidelines "Common tested interferences are endogenous: bilirubin for icterus, lipid for lipemia, and hemoglobin... most big labs will release your results and flag something."
Sample Mix-Up / Mislabeling PRE-ANALYTICAL Results completely inconsistent with patient's clinical condition or previous values Wrong patient label on tube; lab transposition error; giving results to wrong client Double-check labels at collection; verify patient identity; if results don't fit, consider sample mix-up before extensive workup "I remember in practice, once I went over the wrong lab results with the wrong owner... diagnosing their cat with kidney disease when their cat was completely normal."
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