Arab Board Clinical Pathology Part 1 common mistakes
Arab Board Clinical Pathology Part 1 · Understand the traps and how to avoid them.
Treating an isolated prolonged aPTT as automatically a factor deficiency and ordering factor assays before checking whether the patient is on heparin or has a lupus anticoagulant.
Trainees memorise the intrinsic cascade and jump straight from prolonged aPTT to factor VIII/IX/XI/XII levels, forgetting that the mixing study result and the clinical context (line flushes, heparin therapy) determine the next step.
What to do instead
Adopt a fixed algorithm: repeat with a 1:1 normal plasma mix; corrects = factor deficiency, does not correct = inhibitor (include lupus anticoagulant with hexagonal phase or two-test approach). Always check medication and line history first.
Reporting a spurious potassium (pseudohyperkalaemia) or spurious glucose without recognising the pre-analytical cause, such as delayed processing, haemolysis, or a drip arm.
Candidates focus on the analyser result and interpret the number as physiological, missing that most laboratory errors are pre-analytical and that potassium rises with haemolysis while glucose falls with delayed separation.
What to do instead
Before interpreting an unexpected value, screen for haemolysis index, sample timing, and collection site; request a repeat from a fresh, non-drip arm and compare with previous results.
Interpreting a positive serology result (e.g., hepatitis B core IgM, HIV antigen/antibody, syphilis) as proof of active disease without applying confirmatory and supplementary testing.
The screening assay is taught as the diagnostic test, and candidates conflate sensitivity with certainty, ignoring false positives from cross-reactivity and the need for confirmatory algorithms.
What to do instead
State the screening-to-confirmation pathway explicitly: reactive screen → confirmatory assay (e.g., Western blot, immunoblot, treponemal/non-treponemal pairing) → interpret with clinical and epidemiological context.
Misclassifying an anaemia by ignoring the reticulocyte count and the MCV, then choosing a workup based on haemoglobin alone.
The anaemia classification framework (microcytic/normocytic/macrocytic plus reticulocyte response) is known in principle but not applied systematically under time pressure.
What to do instead
Force a two-step grid every time: MCV category then reticulocyte index (high = blood loss/haemolysis, low = production defect); let the grid dictate iron studies, B12/folate, or haemolysis screen.
Selecting the wrong Westgard rule to detect a specific error type - e.g., using 1-2s as a rejection rule rather than a warning rule, or missing that 2-2s detects systematic error while R-4s detects random error.
Rules are memorised as a list without linking each rule to the error it detects or to the number of control observations required.
What to do instead
Learn each rule by its error signature: 1-2s warning, 1-3s random, 2-2s systematic, R-4s random, 4-1s and 10x systematic. Practise reading Levey-Jennings plots and naming the rule and error type.
Confusing sensitivity, specificity, positive predictive value, and prevalence effects - e.g., claiming a highly sensitive test rules out disease regardless of pre-test probability.
Formulas are learned in isolation without the clinical framing that predictive values depend on prevalence while sensitivity and specificity do not.
What to do instead
Rehearse with 2x2 tables and a fixed script: sensitivity/specificity are test properties; PPV/NPV shift with prevalence. Apply likelihood ratios to a stated pre-test probability.
Mishandling a suspected acute transfusion reaction by stopping at 'febrile non-haemolytic reaction' without checking clerical error, doing a direct antiglobulin test, and inspecting for haemolysis.
The differential is memorised as a list, but the mandatory immediate steps (stop transfusion, clerical check, DAT, visual inspection, culture) are not rehearsed as a sequence.
What to do instead
Memorise the immediate action bundle: stop, maintain access, clerical check, return unit and samples, DAT plus repeat ABO, plasma free haemoglobin, and cultures for suspected sepsis.
Interpreting a molecular/genetic result (e.g., a variant of uncertain significance or a heterozygous carrier state) as diagnostic of disease without considering inheritance pattern and penetrance.
Candidates treat any detected variant as pathogenic, skipping classification frameworks and the distinction between carrier, affected, and uncertain findings.
What to do instead
Apply ACMG-style classification logic and state the inheritance model (autosomal recessive vs dominant) before interpreting; explicitly label VUS as non-diagnostic.
Ignoring biosafety and waste/chemical hazard classification when answering method or management questions - e.g., assuming all specimens can be handled at BSL-2 or that all chemical waste is drain-disposable.
Safety content is skimmed as common sense, so risk-group classification, spill procedures, and waste segregation are not linked to specific agents and regulations.
What to do instead
Build a short reference table: risk group to biosafety level, spill response by agent type, and chemical waste categories; practise classifying sample scenarios.
Misapplying quality-control statistics - e.g., using the wrong standard deviation source, confusing coefficient of variation with standard deviation, or accepting a method because the mean matches without checking imprecision.
Statistical formulas are memorised without the operational meaning of SD (from the QC data) versus CV (SD/mean) and without linking them to allowable error and sigma metrics.
What to do instead
Practise computing mean, SD, and CV from a small QC dataset, then compare total allowable error against observed imprecision and bias to decide acceptability.