TEPAC Patologia Clínica common mistakes
TEPAC Patologia Clínica · Understand the traps and how to avoid them.
Reporting a laboratory result without checking whether it fits the patient's clinical picture or whether it is physiologically plausible (for example, accepting a potassium of 7.8 mmol/L in a well-appearing outpatient without questioning a possible hemolyzed sample).
Candidates trained to interpret isolated values treat each number as ground truth and skip the pre-analytical plausibility check, so they miss specimen artifacts and transcription errors that a clinician would catch instantly.
What to do instead
Before committing to an interpretation, run a rapid plausibility screen: compare the value against reference range, expected direction of change, and sample quality indicators (hemolysis index, lipemia, icterus). If implausible, state the likely pre-analytical cause and the recommended repeat or alternative specimen.
Choosing the wrong anticoagulant tube for a test (for example, using EDTA plasma for calcium or alkaline phosphatase, or citrate for a coagulation test drawn into a partially filled tube).
Candidates memorize tube colors superficially and do not connect the additive's chemical action (EDTA chelates divalent cations; citrate binds calcium; oxalate precipitates calcium) to the analyte being measured.
What to do instead
Build a one-page matrix linking each additive to its mechanism of interference and the analytes it distorts. Practice classifying any requested test by the additive it tolerates, and always verify fill volume for citrate tubes because the 9:1 blood-to-anticoagulant ratio is critical.
Interpreting a single abnormal coagulation value (for example, an isolated prolonged aPTT) as a diagnosis rather than as a screening signal requiring a mixing study or factor assay.
Candidates conflate screening tests with confirmatory tests and do not recall that aPTT prolongation can reflect factor deficiency, inhibitor, lupus anticoagulant, or pre-analytical heparin contamination.
What to do instead
Adopt a stepwise algorithm: repeat to exclude error, perform a 1:1 mixing study (correction indicates factor deficiency; failure to correct indicates inhibitor), then proceed to specific factor assays or inhibitor testing. State the algorithm explicitly in answers.
Misreading the direction of a shift in a quality-control chart, such as calling a trend of seven consecutive points on one side of the mean 'in control' because each point is within two standard deviations.
Candidates focus only on individual point limits and forget the Westgard multirule logic, where systematic error is detected by runs, trends, and shifts even when no single point exceeds the control limit.
What to do instead
Memorize and apply the multirules explicitly: 1-3s, 2-2s, R-4s, 4-1s, and 10x. For each flagged pattern, name whether it indicates random or systematic error and state the corrective action (recalibrate, new reagent lot, maintenance).
Confusing analytical sensitivity with clinical sensitivity and specificity when evaluating a new assay, and therefore recommending a test solely because it detects very low concentrations.
Candidates conflate the limit of detection with diagnostic performance and do not separate analytical validation from clinical validation.
What to do instead
Define each term before answering: analytical sensitivity is the smallest detectable amount; clinical sensitivity is the proportion of diseased patients who test positive; specificity is the proportion of healthy patients who test negative. Use a 2x2 table to compute predictive values and explain how prevalence changes them.
Calculating or interpreting a positive and negative predictive value without accounting for disease prevalence, then presenting the PPV as if it were an intrinsic test property.
Candidates memorize the formulas but do not internalize that predictive values depend on the population tested, so they apply values from one setting to another.
What to do instead
Always state the prevalence assumption, compute PPV and NPV from sensitivity, specificity, and prevalence, and explain how a low-prevalence screening population lowers PPV even for an excellent test. Mention confirmatory testing as the remedy.
Failing to separate pre-analytical, analytical, and post-analytical causes when troubleshooting an erroneous result, and instead blaming the instrument immediately.
Candidates jump to the analyzer because it is the most visible component, overlooking that most laboratory errors occur before and after analysis.
What to do instead
Use a structured checklist in order: patient identification and collection, transport and storage, sample integrity, reagent and calibration status, instrument flags, then result verification and reporting. Assign each candidate cause to its phase explicitly.
Interpreting a urinalysis by reading each dipstick pad in isolation without correlating it with microscopy and with the patient's hydration status.
Candidates treat the dipstick as a panel of independent results and do not integrate findings such as a positive leukocyte esterase with nitrite, pH, and the presence of squamous epithelial cells indicating contamination.
What to do instead
Read the urinalysis as a pattern: combine chemical pads, microscopic findings, and collection quality. Explicitly state when a result suggests contamination or needs a clean-catch repeat, and link each pattern to a likely clinical correlate.
Reporting a critical value or markedly abnormal result without triggering the required communication step, or documenting it without confirming who received it.
Candidates focus on the analytical interpretation and treat reporting as an administrative afterthought, forgetting that critical value notification is part of the laboratory's clinical responsibility.
What to do instead
For any critical result, state the value, the reference threshold it breaches, the person notified, the time, and the read-back confirmation. Treat this as a mandatory element of the answer whenever a life-threatening abnormality appears.
Managing time by answering long interpretive cases first and leaving short factual items unanswered, or changing correct first answers on review without a concrete reason.
Candidates underestimate the reading load of case-based items and let anxiety drive answer switching, which research on testing behavior shows often converts right answers into wrong ones.
What to do instead
Do a first pass answering every item, flagging uncertain ones, and never leaving blanks. On review, change an answer only when a specific new fact or misread word is identified. Practice with timed full-length sets to calibrate pacing.