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CMSA: Diagnostic Testing and Laboratory Procedures

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Diagnostic Testing and Laboratory Procedures

What the domain tests

Diagnostic Testing and Laboratory Procedures covers patient preparation, specimen collection and handling, order of draw, waived testing, quality control, and basic procedures such as ECG and spirometry.

Core rules

  • Venipuncture order of draw: blood culture bottles, light blue (citrate), serum tube (gold or red), green (heparin), lavender (EDTA), gray (fluoride/oxalate). Fill tubes to the marked volume, especially citrate.
  • Invert tubes gently the recommended number of times; never shake. Label at the bedside with two identifiers, date, time, and your initials.
  • Confirm preparation (fasting, holding medications), verify the order, and explain the procedure. Document collection time, site, and any difficulty.
  • Capillary puncture: warm the site, wipe away the first drop, puncture the side of the fingertip, and avoid the thumb and index finger in infants. Neonatal heel sticks stay within the medial or lateral heel.
  • CLIA-waived tests (glucose, urine dipstick, rapid strep, PT/INR, hemoglobin, pregnancy) still require a written procedure, controls, and documented results and QC.
  • Fasting specimens generally require 8-12 hours. A 24-hour urine collection is kept cold and is discarded and restarted if a void is missed.
  • ECG: limb leads RA, LA, LL, RL; precordial V1-V6 across the chest; patient supine, skin dry and lotion-free, still and quiet. Artifact comes from movement, poor contact, or muscle tremor.
  • Treat every specimen as potentially infectious: biohazard bag, gloves, and no needle recapping.

Worked example

You must draw a citrate tube and an EDTA tube. Reasoning: coagulation studies are highly sensitive to order and fill volume. Draw the light blue tube before the lavender one, fill it to the line, and invert gently three to four times. Drawing lavender first risks EDTA carryover, which falsely lowers calcium-dependent clotting results.

Traps that cost marks

  • Underfilling citrate tubes, which falsely prolongs clotting times.
  • Labeling tubes after leaving the patient's side.
  • Reporting a waived test without running controls.
  • Allowing an ECG patient to talk during the tracing.