1. How long should a standard serum collection tube be allowed to clot at room temperature before centrifugation?
Answer: A
According to CLSI guidelines, standard serum collection tubes require 30 to 60 minutes at room temperature to achieve complete clot formation before centrifugation, which prevents fibrin strands from contaminating the serum. Allowing 15 to 20 minutes is still too short for normal whole blood in a standard serum tube to fully retract and form a solid clot. Waiting 2 to 3 hours exceeds the recommended timeframe and can lead to cell metabolism artifacts, such as decreased glucose and increased potassium levels, due to prolonged contact with red blood cells. Allowing only 5 to 10 minutes is insufficient for standard serum tubes; centrifuging too soon results in incomplete clot formation, fibrin strands, and potential hemolysis (though rapid thrombin tubes can clot in this timeframe).
2. According to CLSI standards, when should a phlebotomist label a blood collection tube?
Answer: A
According to CLSI and NHA standards, blood collection tubes must be labeled immediately after collection at the bedside in the presence of the patient. Labeling before leaving the patient guarantees positive patient identification and prevents specimen mix-up. Labeling right after centrifuging creates unlabeled specimens in the lab, which is an immediate cause for specimen rejection because positive identification cannot be guaranteed once tubes leave the patient's side. Labeling during transport away from the patient violates bedside labeling protocols and introduces a high risk of misidentification. Pre-labeling tubes prior to venipuncture is a serious safety violation. If the venipuncture attempt is unsuccessful or aborted, an unused pre-labeled tube left on the phlebotomy tray could mistakenly be filled with another patient's blood, causing severe diagnostic and treatment errors.
3. When collecting and processing a specimen for a legal blood alcohol test, the phlebotomist should NOT:
Answer: A
The technician must not uncap or aliquot the primary specimen tube because exposure to room air causes volatile ethanol to evaporate, falsely lowering test results, and breaks the chain-of-custody integrity required for legal admissibility. Using povidone-iodine is correct because non-alcoholic antiseptics must be used to avoid falsely elevating the blood alcohol concentration. Candidates often confuse this by mistaking povidone-iodine's interference with chemistry dermal tests (such as potassium or uric acid) for an antiseptic restriction. Completely filling the tube is correct because it minimizes air space (headspace) where volatile alcohol could escape into the gas phase. Candidates often mistakenly believe tubes should have unfilled headspace to facilitate laboratory mixing. Applying a tamper-evident seal across the stopper and tube body is a mandatory chain-of-custody procedure ensuring that any unauthorized opening is immediately detectable. Candidates may mistakenly assume sealing occurs only at the reference laboratory.
4. A specimen is rejected by the laboratory due to an 'icteric' appearance. Which substance causes this condition?
Answer: A
The term 'icteric' describes serum or plasma that has a deep yellow, amber, or brownish-green tint caused by elevated levels of bilirubin. Per CLSI standards, excessive bilirubin can cause significant photometric interference during automated chemical analysis, resulting in specimen rejection. Hemoglobin released from damaged erythrocytes causes 'hemolysis,' which imparts a pink to deep red tint to serum or plasma rather than an icteric discoloration. Triglycerides and other blood lipids cause 'lipemia,' which makes serum or plasma appear cloudy, turbid, or milky white rather than icteric. Fibrinogen is a clotting protein that produces fibrin strands and micro-clots in poorly mixed or under-anticoagulated tubes, leading to rejection for clotting rather than an icteric appearance.
5. Which term describes applying multiple drops of blood to the same circle on a newborn screening card?
Answer: D
Layering occurs when a phlebotomist applies successive drops of blood to the same filter paper circle. Per CLSI standards (NBS01), each circle must be filled with a single, large drop of blood; layering creates uneven analyte concentration and invalidates the newborn screening test. Milking refers to excessive squeezing or pumping of the infant's heel during a capillary collection, which causes hemolysis and tissue fluid contamination rather than filter paper over-application. Caking refers to blood clotting or heavily crusting on the surface of the filter paper without properly absorbing through to the back side, rather than the specific process of adding multiple successive drops. Haloing refers to a pale serum or fluid ring appearing around the blood spot, typically caused by failing to let the alcohol dry completely before puncture or excessive interstitial fluid contamination.
6. What is the minimum drying time required for a newborn screening collection card before transport?
Answer: B
Per CLSI NBS01 standards, newborn screening filter paper cards must air-dry horizontally on a clean, flat surface at room temperature for a minimum of 3 hours before packaging or shipment. Thirty minutes is the standard clotting time recommended for serum tubes without clot activators before centrifugation, not the required drying duration for filter paper cards. Twenty-four hours represents the minimum feeding duration an infant needs before PKU specimen collection to allow detectable metabolite buildup, not the drying time of the paper card. One hour is insufficient drying time; enclosing a damp Guthrie card inside a transport envelope promotes mold growth and specimen degradation, causing laboratory rejection.
7. When preparing an ammonia specimen for transport to the laboratory, the phlebotomist should:
Answer: D
Ammonia is a temperature-sensitive analyte that red blood cells continue to produce through deamination after collection. Per CLSI guidelines, the specimen must be placed immediately in a crushed ice-water slurry to slow cellular metabolism and maintain sample viability. Placing a tube directly on solid ice cubes leaves air pockets that cause uneven cooling and can freeze red blood cells against the glass, causing hemolysis that falsely elevates ammonia levels. Maintaining a sample at 37° C is required for cold agglutinins and cryoglobulins to prevent premature agglutination, but warmth accelerates red cell metabolism and rapidly increases ammonia concentrations. Protecting a specimen from light with foil or an amber container is necessary for light-sensitive analytes like bilirubin and vitamin B12, but it does not address the metabolic breakdown that alters ammonia levels.
8. According to CLSI standards, serum or plasma should be separated from cells within a maximum of how many hours after collection?
Answer: C
CLSI standards mandate that serum or plasma be physically separated from contact with cells within a maximum of 2 hours from collection. Exceeding this limit causes in vitro cellular metabolism to alter test results, notably causing falsely decreased glucose and falsely elevated potassium. Although processing specimens promptly after full clot formation is ideal, 1 hour is not the formal CLSI maximum threshold. Allowing unseparated whole blood to stand for 3 hours exceeds the allowable limit and leads to significant glycolysis and intracellular electrolyte leakage. A 4-hour delay before centrifugation and separation is far beyond the standard limit and will compromise specimen integrity.
9. A phlebotomist is instructing a patient on collecting a semen specimen for fertility testing. The phlebotomist should instruct the patient to:
Answer: B
Per CLSI and WHO guidelines tested on the NHA CPT exam, the patient must abstain from ejaculation for 2 to 7 days (48 to 168 hours) before collection. This abstinence window provides an accurate baseline for optimal sperm count, motility, and volume. Delivering the sample within 4 hours is incorrect because sperm degrade quickly at ambient conditions. Semen specimens must reach the laboratory within 1 hour (ideally within 30 to 60 minutes) of collection to ensure accurate motility evaluation. Placing the specimen on ice is incorrect because chilling destroys sperm viability and motility. Semen specimens must be maintained near body temperature (approximately 37°C / 98.6°F) during transport, often by carrying the container inside a coat pocket close to the body. Collecting into a standard latex condom is incorrect because commercial condoms contain spermicidal agents, lubricants, or powders that kill sperm and invalidate fertility testing. The specimen should be collected directly into a sterile, wide-mouth container via masturbation.
10. At what temperature should a blood specimen for a cold agglutinin titer be maintained prior to collection?
Answer: D
37°C (98.6°F) is correct because cold agglutinins are autoantibodies that bind to red blood cells at reduced temperatures. Per CLSI guidelines, the collection tube must be pre-warmed and kept at body temperature (37°C) until serum separation so the antibodies remain in the serum. 0°C (32°F) is incorrect because an ice slurry is used for chilled specimens such as ammonia and lactic acid. Cooling a cold agglutinin sample will cause antibodies to prematurely bind to red blood cells, falsely lowering the titer in the serum. 4°C (39.2°F) is incorrect because this represents standard laboratory refrigerator temperature. Refrigerating the specimen will cause agglutination and absorption of antibodies onto red cells before processing. 22°C (71.6°F) is incorrect because ambient room temperature is lower than normal core body temperature, which allows cold-reacting autoantibodies to bind erythrocytes and compromise test integrity.
11. Which of the following is the correct order of draw (first to last) when collecting a serum chemistry screen, a complete blood count (CBC), and a blood alcohol level?
Answer: B
According to CLSI guidelines, the proper order of draw is serum tube (red top), followed by EDTA (lavender top), and finally glycolytic inhibitor (gray top). Gray top tubes containing sodium fluoride and potassium oxalate used for blood alcohol testing are drawn last among routine venipunctures to prevent additive carryover into preceding tubes. Drawing the gray top first violates standard order of draw; sodium fluoride and potassium oxalate would contaminate subsequent tubes, severely altering chemistry and hematology results. Placing the gray top before the lavender top is incorrect because potassium oxalate and sodium fluoride can distort red blood cell morphology and invalidate the CBC. Drawing the lavender top before the red top is incorrect because EDTA carries over into serum tubes, falsely binding calcium and elevating potassium levels.
12. A phlebotomy technician is recording daily quality control measurements. What is the acceptable temperature range for a laboratory refrigerator storing blood specimens?
Answer: C
According to CLSI guidelines, standard laboratory refrigerators used for specimen preservation and reagent storage must be maintained at 2°C to 8°C (36°F to 46°F). Temperature readings must be documented on a daily log to ensure specimen integrity. This range represents controlled room temperature (59°F to 86°F), which is appropriate for storing dry diagnostic test kits and collection supplies, not refrigerated specimens. This range represents standard laboratory freezer storage used for frozen serum or plasma aliquots. Storing whole blood at -20°C to -10°C causes red blood cells to freeze and hemolyze. This range represents normal human body temperature (95°F to 98.6°F) and is used for laboratory incubators, such as those incubating blood cultures, rather than refrigeration.
13. When collecting a throat culture, which of the following is the correct sequence of steps?
Answer: B
Per NHA and CLSI procedural guidelines for throat culture collection, the phlebotomist must first depress the tongue using a sterile depressor to clearly visualize the target area and avoid oral contamination. Next, the swab is rubbed across the tonsillar areas and posterior pharynx. The swab is then inserted into the sterile transport sleeve, and finally the ampule at the base is crushed to release the transport medium and preserve organism viability. Beginning by crushing the ampule reflects the misconception that the transport medium must be pre-activated or that the swab should be moistened prior to collection. Activating the ampule before swabbing risks leakage, contamination, and loss of the transport fluid. Crushing the ampule between depressing the tongue and swabbing the tonsillar area reflects confusion about specimen preservation timing. The swab must remain dry and sterile until it contacts the mucosal surface, and the ampule should only be crushed once the swab is seated inside the tube. Crushing the ampule before inserting the swab into the transport tube reflects the misconception that transport fluid should be released into an empty container. Crushing the ampule before securing the swab inside can cause the liquid medium to spill or escape through the open tube top.
14. At which of the following temperatures should a phlebotomist maintain a specimen collected for a cold agglutinin titer?
Answer: A
Cold agglutinins are antibodies that attach to red blood cells at temperatures below body temperature. Per CLSI guidelines, the collection tube must be pre-warmed and maintained at 37° C (98.6° F) until serum separation so the antibodies remain in the serum for accurate testing. Ambient room temperature (20° C to 25° C) is too cool for cold agglutinins. Candidates often assume standard room-temperature transport is sufficient, but temperatures below 37° C cause the autoantibodies to bind red blood cells and precipitate out of the serum. An ice slurry (0° C) is used for chilled specimens such as ammonia, lactic acid, and blood gases. Confusing cold agglutinins with chilled analytes is a common mistake; placing this specimen on ice causes rapid agglutination and destruction of test integrity. This range represents standard refrigerator storage. Candidates frequently select refrigeration because of the word 'cold' in the test name, but chilling this specimen causes complete agglutination and invalidates the result.
15. How many times should a phlebotomist invert a light blue top tube containing sodium citrate immediately after collection?
Answer: D
According to CLSI guidelines, tubes containing sodium citrate require 3 to 4 gentle inversions immediately following collection to prevent clotting while avoiding hemolysis and platelet activation. Inverting 5 to 6 times reflects the protocol for serum separator tubes (SSTs) containing clot activators, rather than light blue coagulation tubes. Inverting 8 to 10 times is the standard requirement for EDTA (lavender/pink), heparin (green), and potassium oxalate/sodium fluoride (gray) tubes, not light blue tubes. Inverting 1 to 2 times is insufficient to properly mix the liquid anticoagulant with the blood, which can lead to microclot formation and specimen rejection.
