RMA Diagnostic Testing and Lab Procedures 2 — Questions and Answers

Question 1: Which anticoagulant additive is found in the LAVENDER (purple) top blood collection tube and is the standard choice for CBC testing?

Heparin
Sodium citrate
EDTA (ethylenediaminetetraacetic acid) (Correct answer)
Sodium fluoride

Correct answer: EDTA (ethylenediaminetetraacetic acid)

Lavender/purple top tubes contain EDTA, which chelates calcium to prevent clotting while preserving cell morphology — making it ideal for complete blood counts (CBC) and blood differential.

Evacuated blood collection tubes are color-coded based on the additive they contain. Lavender (purple) top tubes contain EDTA (ethylenediaminetetraacetic acid), a chelating agent that binds calcium ions and prevents coagulation. Because EDTA preserves red blood cell and white blood cell morphology without causing cell lysis, it is the preferred anticoagulant for hematology testing including the CBC, blood differential, reticulocyte count, and hemoglobin A1c. Other common tube additives: Red top = no additive (serum separator tubes have gel); Light blue top = sodium citrate (coagulation studies — PT/INR, aPTT); Green top = heparin (plasma chemistry tests); Gray top = sodium fluoride (glucose preservation); Yellow top = ACD or SPS (blood cultures or special studies). The order of draw when collecting multiple tubes from a single venipuncture must be followed precisely to prevent additive carryover. CLSI-recommended order: blood cultures → light blue → red/SST → green → lavender → gray. Medical assistants must memorize tube types, additives, and their associated tests for both specimen collection competency and the RMA exam.

Question 2: A urine dipstick test shows positive nitrite and positive leukocyte esterase. What do these findings MOST strongly suggest?

Diabetes mellitus
Kidney stones
Urinary tract infection (Correct answer)
Dehydration

Correct answer: Urinary tract infection

Positive nitrite (indicating bacteria that convert urinary nitrates) combined with positive leukocyte esterase (indicating white blood cells) is highly suggestive of a bacterial urinary tract infection.

The urine dipstick is a rapid, point-of-care screening tool that analyzes multiple analytes simultaneously. Two markers are particularly important for UTI detection: nitrite and leukocyte esterase. Leukocyte esterase is an enzyme released by white blood cells (neutrophils), so a positive result indicates pyuria (WBCs in the urine), which is a hallmark of urinary tract infection. Nitrites are produced when gram-negative bacteria (especially Escherichia coli, the most common UTI pathogen) convert urinary nitrates to nitrites; a positive result indicates bacterial colonization. When both are positive, the sensitivity and specificity for UTI are substantially higher than either marker alone. The physician will typically confirm with a urine culture and sensitivity to identify the specific organism and guide antibiotic selection. Medical assistants should collect clean-catch midstream urine specimens correctly (patient education on technique is critical), process specimens promptly to prevent bacterial overgrowth artifacts, and document all dipstick results accurately.

Question 3: A point-of-care glucose meter reads 'HI' for a patient's blood glucose. What does this result mean and what action should the medical assistant take?

The reading is within a high-normal range; document and continue
The glucose exceeds the meter's upper measurement limit; report the result to the provider immediately (Correct answer)
The battery is low; replace the battery and retest
The test strip has expired; use a new strip and retest

Correct answer: The glucose exceeds the meter's upper measurement limit; report the result to the provider immediately

A 'HI' reading means the blood glucose is above the maximum measurable range of the meter (typically 600 mg/dL) — this is a critical value requiring immediate provider notification.

Point-of-care glucose meters have defined measurement ranges, typically 20–600 mg/dL. When the blood glucose exceeds the upper limit, the meter displays 'HI' (or 'HIGH') to indicate the reading is above the reportable range. A glucose this high (hyperglycemia) can indicate diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), or severe uncontrolled diabetes — all potentially life-threatening emergencies. The appropriate response is: do not dismiss the result, immediately inform the supervising provider with the exact result ('HI — above the meter's upper limit of [X] mg/dL'), prepare for the provider to order a confirmatory venous glucose through the laboratory, and be ready to assist with urgent management protocols. Similarly, a 'LO' result indicates glucose below the lower reportable limit (typically 20 mg/dL), representing severe hypoglycemia, also a medical emergency. Medical assistants must recognize critical meter readings and follow the practice's critical value reporting protocol without delay.

Question 4: Which of the following is the CORRECT procedure for collecting a throat culture specimen?

Swab the inside of both cheeks and the tongue
Depress the tongue and swab the posterior pharynx and tonsillar area (Correct answer)
Insert the swab into the nostril and rotate
Have the patient gargle with saline and spit into a specimen cup

Correct answer: Depress the tongue and swab the posterior pharynx and tonsillar area

A throat culture requires swabbing the posterior pharynx and tonsillar pillars where group A Streptococcus (strep throat) and other pathogens are found; the cheeks and tongue are not appropriate collection sites.

Throat cultures are most commonly performed to detect group A beta-hemolytic Streptococcus (GABHS/Strep pyogenes), the causative agent of strep pharyngitis. Proper collection technique directly affects test sensitivity. The correct procedure: use a tongue depressor to hold the tongue down and provide visualization, have the patient say 'ahhh' to elevate the soft palate, then firmly swab the posterior pharynx (back of the throat) and both tonsillar pillars/crypts in a sweeping motion, avoiding the lips, cheeks, teeth, and tongue. Avoid touching the uvula, which can trigger gagging. For rapid strep antigen tests, two swabs are typically collected simultaneously — one for the rapid test and one to be plated for culture in case the rapid test is negative. The swab must be transported in the appropriate transport medium if not immediately plated. The medical assistant must use proper PPE (gloves, mask) given potential aerosol generation when patients cough or gag during collection.

Question 5: When performing a capillary blood collection (fingerstick), which finger is preferred and what is the CORRECT puncture site?

Index finger, at the very tip
Ring finger, lateral aspect of the fingertip (avoiding the center) (Correct answer)
Thumb, on the pad
Little finger, on the medial side

Correct answer: Ring finger, lateral aspect of the fingertip (avoiding the center)

The ring finger (or middle finger) lateral aspect is preferred because it has adequate tissue depth and fewer nerve endings than the index finger or fingertip center, reducing patient discomfort.

For adult capillary blood collection, CLSI guidelines recommend the third (middle) or fourth (ring) finger of the non-dominant hand as the preferred site. The lateral or medial aspect of the fingertip pad (not the center tip) is used because: the center of the fingertip has more nerve endings (more painful), the center has less tissue depth, and lateral punctures heal more easily. The index finger is avoided because it is heavily used in daily activities, making healing slower and punctures more painful. The thumb has a pulse and may give arterial rather than capillary blood. The little finger has thin tissue layers close to bone, increasing the risk of hitting the periosteum. In infants, heel punctures (not fingersticks) are used; the medial or lateral plantar surface of the heel is the correct site, strictly avoiding the posterior curve of the heel (Achilles tendon area) to prevent calcaneal periostitis or osteomyelitis. Medical assistants must know correct site selection for both adult and pediatric capillary collection.

Question 6: A patient's fasting lipid panel shows total cholesterol 220 mg/dL, LDL 145 mg/dL, HDL 38 mg/dL, and triglycerides 185 mg/dL. Which single finding is MOST concerning for cardiovascular risk?

Total cholesterol of 220 mg/dL
LDL of 145 mg/dL
HDL of 38 mg/dL (Correct answer)
Triglycerides of 185 mg/dL

Correct answer: HDL of 38 mg/dL

HDL of 38 mg/dL is below the desirable threshold of 40 mg/dL for men (50 mg/dL for women); low HDL is an independent risk factor for cardiovascular disease because HDL removes cholesterol from arterial walls.

Lipid panel interpretation requires understanding the role of each component. Total cholesterol below 200 mg/dL is desirable; 200–239 mg/dL is borderline high; 240+ mg/dL is high. LDL ('bad' cholesterol) below 100 mg/dL is optimal; 130–159 mg/dL is borderline high. Triglycerides below 150 mg/dL are normal; 150–199 mg/dL is borderline high. HDL ('good' cholesterol) is the inverse — higher levels are protective. HDL below 40 mg/dL in men (below 50 mg/dL in women) is considered a risk factor for coronary artery disease (CAD). HDL carries cholesterol from the arterial walls back to the liver for excretion (reverse cholesterol transport). Low HDL is an independent, modifiable cardiovascular risk factor that can be addressed through exercise, smoking cessation, and medication. While all values in this panel are suboptimal, the HDL of 38 mg/dL is categorically below the risk threshold. The other values are borderline or mildly elevated. Medical assistants do not interpret labs but must understand reference ranges to identify critical and abnormal values for timely provider notification.

RMA Diagnostic Testing and Lab Procedures 2

Which anticoagulant additive is found in the LAVENDER (purple) top blood collection tube and is the standard choice for CBC testing?