NCMA Basic Laboratory Procedures and Specimen Handling 2 — Questions and Answers

Question 1: What is the correct temperature range for refrigerating urine specimens awaiting analysis?

2°C to 8°C (Correct answer)
10°C to 15°C
15°C to 20°C
20°C to 25°C

Correct answer: 2°C to 8°C

Urine specimens must be refrigerated at 2°C to 8°C to preserve cellular elements and prevent bacterial overgrowth if not analyzed within one hour of collection.

When a urine specimen cannot be analyzed immediately, refrigeration at 2–8°C slows bacterial multiplication and preserves casts, cells, and chemical analytes. Beyond two hours at room temperature, bacteria proliferate, pH rises, and glucose may be consumed by organisms, leading to false results. Always label the specimen with collection time and refrigerate promptly.

Question 2: Which type of specimen tube contains EDTA as an anticoagulant?

Lavender/purple top (Correct answer)
Red top
Green top
Gray top

Correct answer: Lavender/purple top

Lavender (purple) top tubes contain EDTA (ethylenediaminetetraacetic acid), which chelates calcium to prevent clotting, making them ideal for complete blood counts (CBC).

EDTA works by binding calcium ions, which are essential for the coagulation cascade. Lavender-top tubes are standard for CBC, differential, and blood film preparations. Green-top tubes contain heparin, red tops have no additive or contain clot activator, and gray tops contain potassium oxalate/sodium fluoride for glucose preservation.

Question 3: What does a quality control (QC) chart help the medical assistant monitor in the laboratory?

Accuracy and precision of test results over time (Correct answer)
Patient demographic information
Supply inventory levels
Physician ordering patterns

Correct answer: Accuracy and precision of test results over time

QC charts (Levey-Jennings charts) plot control values over time to identify trends, shifts, or random errors that may indicate problems with reagents, instruments, or technique.

A Levey-Jennings chart displays daily or run-based control results against established mean and standard deviation limits (±2SD warning, ±3SD rejection). Westgard rules help interpret patterns: a shift of 6 consecutive points on one side of the mean suggests systematic error, while random scatter exceeding 2SD on alternating sides suggests random error. Regular QC prevents reporting inaccurate patient results.

Question 4: Which specimen is used for a fasting blood glucose test?

Serum or plasma from a venipuncture after 8–12 hours of fasting (Correct answer)
Random urine collected any time
Capillary blood collected immediately after a meal
24-hour urine collected over a full day

Correct answer: Serum or plasma from a venipuncture after 8–12 hours of fasting

A fasting blood glucose requires the patient to abstain from food and caloric beverages for 8–12 hours prior to collection; serum or plasma is then obtained by venipuncture.

Fasting ensures that postprandial glucose elevation does not interfere with the baseline measurement. Normal fasting plasma glucose is 70–99 mg/dL; 100–125 mg/dL indicates prediabetes; ≥126 mg/dL on two occasions indicates diabetes. Gray-top tubes (sodium fluoride) are preferred if processing is delayed because fluoride inhibits glycolysis, preserving the glucose level.

Question 5: What is the purpose of the chain of custody procedure for laboratory specimens?

To document every person who handled the specimen to ensure legal integrity (Correct answer)
To speed up processing time
To reduce the cost of laboratory testing
To prevent specimen refrigeration

Correct answer: To document every person who handled the specimen to ensure legal integrity

Chain of custody documents every individual who collected, transferred, or handled a specimen, ensuring legal defensibility particularly for drug testing, forensic, or workplace samples.

Chain of custody requires that specimens be collected in front of a witness, sealed with tamper-evident tape, labeled with the collector's initials and date/time, and accompanied by a form signed at each transfer. Any break in the chain can render results inadmissible in court. Medical assistants must follow strict chain-of-custody protocols for pre-employment drug screens and legally ordered tests.

Question 6: When centrifuging a blood specimen to obtain serum, what must occur before centrifugation?

The blood must be allowed to clot completely (30 minutes) (Correct answer)
The specimen must be frozen first
The tube must be inverted 20 times
The additive must be removed from the tube

Correct answer: The blood must be allowed to clot completely (30 minutes)

For serum separation, blood in a red-top or SST tube must clot fully (approximately 30 minutes at room temperature) before centrifugation; premature spinning yields incomplete serum separation.

If a clot activator (SST tube) is used, clotting occurs within 5 minutes, but most red-top tubes require 30 minutes. After clotting, centrifugation at approximately 1,000–1,200 × g for 10 minutes separates the clot (with cells) from the liquid serum. Insufficient clotting time causes fibrin strands in the serum, clogging analyzers and producing erroneous results.

NCMA Basic Laboratory Procedures and Specimen Handling 2

What is the correct temperature range for refrigerating urine specimens awaiting analysis?