Laboratory Quality Control and Management Flashcards

Four consecutive control results all exceed +1 SD from the mean. Which Westgard rule is violated, and what type of error does it suggest?

Answer: 4-1s, systematic error

The 4-1s rule flags four consecutive values beyond the same 1 SD limit, which points to systematic error.

Right after a new reagent lot is put in use, the Levey-Jennings chart suddenly shows seven straight control values above the mean. What pattern is this?

Answer: Shift

An abrupt move of the mean with consecutive values on one side is a shift, often caused by a new reagent or calibrator lot.

Under CLIA, what minimum proficiency testing score is generally required for satisfactory performance on most regulated analytes?

Answer: 80%

Most regulated analytes need at least 80%; ABO/Rh and compatibility testing need 100%.

A glucose control has a mean of 250 mg/dL and a standard deviation of 5 mg/dL. What is the coefficient of variation?

Answer: 2%

CV = (SD / mean) x 100 = (5/250) x 100 = 2%.

A patient's MCV changes from 88 fL to 68 fL within 24 hours. Which QC tool is designed to catch this, and what problem does it most likely reveal?

Answer: Delta check; specimen misidentification

Delta checks compare a result with the patient's earlier values, and a large unexplained change suggests a mislabeled or wrong specimen.

A new assay gives these results: TP = 90, FN = 10, TN = 180, FP = 45. What is its specificity?

Answer: 80%

Specificity = TN / (TN + FP) = 180/225 = 80%.

Using CLSI's 20-sample method to verify a manufacturer's reference interval, when can the lab accept the interval?

Answer: No more than 2 of 20 results fall outside the interval

Under CLSI EP28, the interval is verified if 2 or fewer of 20 healthy-subject results fall outside it.