MELE common mistakes
MELE · Understand the traps and how to avoid them.
When a forward ABO typing shows agglutination but the reverse (serum) typing does not match, the candidate records the forward result as the patient's blood type and moves on instead of investigating the discrepancy.
Forward typing is taught first and relies on strong, obvious agglutination, so it feels authoritative. Candidates forget that the reverse grouping is an independent check and that a mismatch signals a subgroup, a cold autoantibody, or a missing isohemagglutinin that must be resolved before any unit is issued.
What to do instead
Treat every forward/reverse discrepancy as a stop point. Systematically rule out technical causes (cell/serum mix-up, wrong incubation), then test with anti-A1 lectin, extended incubation at room temperature and 4 C, and an autocontrol. Document the resolution and, if unresolved, report the discrepancy and consult the reference laboratory before transfusion.
A positive antibody screen is reported as positive without determining whether the reactivity is in the screen cells only, the autocontrol, or both, and without identifying the antibody specificity.
Candidates stop at 'screen positive' because that is the visible endpoint. They do not appreciate that the autocontrol and panel workup distinguish an alloantibody needing antigen-negative units from an autoantibody or a warm/cold autoagglutinin, and that unidentified antibodies delay safe transfusion.
What to do instead
Always run the autocontrol alongside the screen. If the screen is positive, proceed to a phenotype/panel: test selected cells to establish a pattern, use enzyme-treated cells and a prewarm technique to separate IgG from cold-reactive antibodies, and identify the specificity before selecting units. Report 'antibody identified' with the antigen status.
On a chemistry result, the candidate accepts an isolated abnormal value (for example a low sodium or high potassium) as a true patient finding without checking for hemolysis, contamination, or a delta from the previous result.
Analyzers flag hemolysis and lipemia, but candidates often dismiss the flag as routine. Hemolysis falsely raises potassium and LDH and lowers sodium, and a value that does not fit the clinical picture is more often preanalytical than pathological.
What to do instead
Before reporting, review the hemolysis/lipemia/icterus index, compare against the prior result (delta check), and correlate with other analytes. If hemolysis is present, repeat from a fresh, properly collected specimen and note the interference. Question any result that is physiologically implausible for the patient.
When calculating an anion gap or an osmolal gap, the candidate uses the wrong reference formula or forgets to convert units, then interprets the number as a diagnosis rather than as a screening calculation.
Different laboratories use different electrolyte panels and reference ranges, and units (mmol/L vs mEq/L, mg/dL vs mmol/L) are easy to mix. Candidates memorize one formula and apply it without checking the lab's own reference interval or the sodium correction.
What to do instead
Use the formula and reference range printed on the report or in the lab's SOP. Show the arithmetic, keep units consistent, and interpret the gap only in the context of the measured electrolytes and clinical picture. For osmolality, remember the calculated gap uses measured osmolality minus calculated osmolality.
A CBC shows a low platelet count or a low hemoglobin, and the candidate reports it without reviewing the histogram, the flagging, or a smear, missing clumping, rouleaux, or a cold agglutinin that explains the abnormality.
Automated counts are trusted as final. Candidates do not know that EDTA-induced platelet clumping causes pseudothrombocytopenia and that cold agglutinins falsely lower RBC and raise MCV, so a spurious result is reported as disease.
What to do instead
For any unexpected low platelet count, examine the smear for clumping and repeat in citrate or heparin. For an unexplained high MCV or low RBC, warm the sample and reanalyze. Review the WBC/RBC/platelet histograms and flags, and correlate with the smear before releasing an abnormal result.
On a Gram stain, the candidate reports organisms as 'gram-positive cocci in clusters' or similar without confirming the Gram reaction, shape, and arrangement under oil immersion, and without correlating with the culture.
Gram stain interpretation is subjective and candidates rush to a category. Decolorization timing, thick smears, and old cultures distort the reaction, and a stain read in isolation can mislead therapy.
What to do instead
Read the stain at 100x oil with a known control slide. Assess decolorization quality, describe shape and arrangement precisely, and state the correlation with the culture and the direct specimen. Report 'no organisms seen' when appropriate rather than guessing.
A positive serology result (for example HIV antigen/antibody, syphilis, or hepatitis) is reported as a diagnosis without the confirmatory or supplemental test, and without considering the preanalytical or biological false-positive causes.
Screening assays are designed for sensitivity, and candidates treat a reactive screen as final. They forget confirmatory algorithms, window periods, and cross-reactivity, which leads to wrong counseling and reporting.
What to do instead
Follow the two-step algorithm: a reactive screen goes to the supplemental/confirmatory assay, and results are interpreted with the clinical and exposure history. Report screening versus confirmed status distinctly, and note that a nonreactive result in the window period does not exclude infection.
On a urinalysis, the candidate reads the dipstick and microscopic results independently and does not reconcile a positive blood or protein dipstick with the absence or presence of formed elements on the sediment.
The chemical and microscopic parts of the urinalysis are complementary, and candidates treat them as separate tests. A positive blood with no RBCs suggests hemoglobinuria or myoglobinuria, and a positive protein with a bland sediment suggests a different mechanism.
What to do instead
Always cross-check dipstick chemistry against the sediment. If blood is positive but RBCs are absent, consider hemoglobin or myoglobin and confirm. If protein is positive, quantify with a protein/creatinine ratio. Note the specimen collection method, since contamination changes the interpretation.
When a quality-control result falls outside the acceptable range, the candidate repeats the control until it passes and then runs patient samples, rather than investigating the root cause.
QC failure feels like an obstacle to be cleared, and repeating is quick. Candidates do not recognize that a shift or trend indicates a systematic problem (reagent, calibration, or instrument) and that releasing patient results after a 'lucky' pass is a compliance and safety breach.
What to do instead
Apply the Westgard rules and the laboratory's QC policy: stop, do not report patient results, and investigate (reagent lot, calibration, maintenance, control handling). Document the investigation and corrective action, and only resume after the cause is resolved and QC is back in control.
On a molecular assay, the candidate reports a detected or not-detected result without checking the internal control, the extraction control, and the limit of detection, and without considering inhibition.
Amplification results look binary, and candidates focus on the target signal. A failed internal control means the negative result is invalid, and a signal near the limit of detection is not a confident positive.
What to do instead
Verify that the internal and extraction controls amplified appropriately before interpreting the target. Reject runs with failed controls, repeat inhibited specimens, and report results only within the validated dynamic range. State the assay's limitations and the need for confirmatory testing where applicable.
The candidate handles a specimen or reagent without the required PPE or spills a biohazard and wipes it up with a dry paper towel, treating the event as routine cleanup.
Candidates focus on the test result and treat safety as background. They underestimate aerosol and surface contamination and do not know the spill response or the exposure-reporting chain.
What to do instead
Follow standard precautions: gloves, gown, eye protection, and a spill kit with absorbent and an appropriate disinfectant (for example freshly prepared hypochlorite) applied with the correct contact time. Report exposures and spills per the laboratory's safety plan and document the event.