ASCP C common mistakes
ASCP C · Understand the traps and how to avoid them.
Interpreting an ABO type from the forward grouping alone when the reverse grouping is weak, discrepant, or not performed.
Forward grouping feels familiar and fast, and candidates often memorize antigen patterns without practicing discrepancy resolution under time pressure.
What to do instead
Compare forward and reverse grouping on every eligible patient; if discrepant, repeat with washed cells, verify patient age/transfusion history, and resolve the discrepancy per SOP before reporting.
Accepting a positive antibody screen as clinically insignificant without antibody identification or antigen-negative crossmatch planning.
Candidates may focus on the positive/negative result and skip the downstream workflow that determines transfusion risk.
What to do instead
Perform antibody identification, rule out common alloantibodies, and select antigen-negative or crossmatch-compatible units as required before release.
Calculating anion gap, osmolality, or corrected calcium with mixed units or without checking for abnormal protein/lipid effects.
Formula recall is strong, but unit conversion and interference checks are often treated as afterthoughts.
What to do instead
Write units beside every value, use the stated formula consistently, and check for conditions such as hyperproteinemia, hyperlipidemia, or hyperglycemia that alter interpretation.
Reporting an automated platelet count without smear review when the analyzer flags clumps, giant platelets, or schistocytes.
Automated results are trusted because they are rapid and precise, and smear review is often skipped when the count is not critically low.
What to do instead
Review the smear for platelet clumps and large platelets whenever flags occur; estimate platelets manually and repeat with citrate or another appropriate method if clumping is present.
Running PT/aPTT on a citrate tube that is underfilled, overfilled, or drawn from a line contaminated with heparin.
Candidates concentrate on analyzer operation and forget that preanalytical tube fill and line contamination are major coagulation error sources.
What to do instead
Verify citrate tube fill against the tube requirement, reject improperly filled tubes, avoid drawing above a heparin line, and correlate unexpected prolongations with specimen quality.
Calling a culture positive from a single colony or mixed growth without assessing colony morphology, quantity, and specimen source.
The presence of growth is treated as the answer, while specimen quality and colonization versus infection are overlooked.
What to do instead
Apply specimen rejection criteria, assess colony morphology and quantity, identify significant isolates, and correlate with Gram stain and clinical source before reporting.
Treating a positive ELISA/CLIA serology result as diagnostic without confirmatory testing or consideration of pretest probability.
Candidates often equate a reactive screening test with disease and may not account for false positives in low-prevalence populations.
What to do instead
Use the appropriate confirmatory or reflex test, interpret results with pretest probability, and recognize that screening assays are designed for sensitivity rather than stand-alone diagnosis.
Ignoring no-template controls, positive controls, or unidirectional workflow when interpreting a molecular amplification result.
The focus is on the patient band or cycle threshold, and contamination controls are treated as routine rather than essential to validity.
What to do instead
Check all controls before accepting a run, repeat invalid or suspicious results, and follow unidirectional workflow and contamination-monitoring procedures.
Answering regulatory or QC questions from memory without verifying the current CLIA/CAP requirement or laboratory policy.
Administration content feels less procedural than bench testing, so candidates rely on vague recollection of thresholds and inspection rules.
What to do instead
Memorize key regulatory categories and thresholds, then practice applying them to scenarios using current checklist language and the laboratory’s written policy.
Drawing tubes out of order, such as collecting an EDTA tube before a citrate or serum tube, and then using the later tube for testing.
Order-of-draw is memorized as a list but not linked to additive carryover and specimen contamination in real draw sequences.
What to do instead
Follow the standard order of draw, fill additive tubes in the correct sequence, and reject specimens when additive carryover or improper collection order could affect results.