Cost types, purchasing controls, and cost of poor quality

Laboratory costs sort along two overlapping axes. The first axis is fixed versus variable: does the cost change with test volume. Fixed costs, salaried staff, facility lease, service contracts, and laboratory information system (LIS) fees, do not change substantially over a relevant volume range. Variable costs, reagents, consumables, calibrators, and shipping, scale with volume. The second axis is direct versus indirect: is the cost traceable to a specific test.

A cost can occupy both axes at once; a dedicated reagent for one assay is fixed and direct if the laboratory pays a flat annual instrument-access fee regardless of volume, or variable and direct if it is billed per test consumed. The basic cost-per-test model states it plainly: cost per test equals total fixed cost divided by test volume, plus variable cost per test.

Because most laboratory fixed costs, staff, lease, and equipment, do not disappear when volume drops, cutting test volume in an existing service line usually saves only the variable-cost portion, not the fixed-cost portion. A budget conversation that assumes volume reduction saves money in proportion to volume is making an error that shows up at year end as an unexplained variance.

CLSI QMS20 organizes laboratory quality-related cost into four categories: prevention (spent before an error occurs, such as SOP design, training, competency assessment, and preventive maintenance), appraisal (spent to detect or measure whether a process meets requirements, such as QC, proficiency testing, audits, and calibration verification), internal failure (an error caught and corrected before the report reaches the customer, such as recollection or discarding an expired reagent), and external failure (an error discovered after the report was released, such as a corrected report or a complaint investigation).

Cost of poor quality (COPQ) is commonly represented as internal failure cost plus external failure cost. The goal is adequate prevention and appraisal spending to reduce the larger failure costs, not to eliminate prevention and appraisal spending, since cutting those categories tends to increase failure cost later.

CLSI QMS21 covers purchasing specification-setting, supplier qualification, receiving inspection, inventory control, and supplier-performance monitoring. It recommends the laboratory define minimum and maximum stock levels, a reorder point, and safety stock for critical items, and that it monitor lead time and stockouts. It also identifies first-expire, first-out (FEFO) stock rotation as the generally preferable method for reagents and consumables carrying an expiration date, and recommends the laboratory maintain contingency plans, such as an approved alternate supplier, for critical items.

A CAP-style accreditation expectation is that reagents, kits, calibrators, and controls are tracked with name, manufacturer, catalog and lot number, expiration date, storage condition, and in-service, quarantine, or rejected status, and that new lots are verified against the previous lot or a suitable reference material before or concurrent with patient use. An item within the manufacturer's printed expiration date is not automatically acceptable for use; storage condition, package integrity, and QC performance must also be acceptable.

A substitute reagent or instrument should never be assumed equivalent merely because it measures the same analyte. FDA guidance on replacement reagents and instrument families states the laboratory must assess intended use, performance, reportable range, and interferences before substitution, and manufacturer substitution guidance during shortages has warned that products should not be substituted by appearance alone, since additive, volume, and construction can differ between comparable-looking items. Every substitution needs laboratory validation before it goes live, cost pressure is not a basis for skipping that step.

A fixed cost stays on the books even after volume falls, prevention or appraisal spending is meant to avoid a larger failure cost later, and no substitute reagent goes into patient testing without laboratory validation, regardless of how urgent the supply gap feels.