Costs can be described in several ways. For example, they can be direct or indirect and fixed or variable. Direct costs are directly traceable to a test procedure, such as reagents, controls, and testing personnel. Indirect costs are costs not directly traceable to a test procedure, such as general operating activities and institutional costs, such as clinical laboratory management, heat, lighting, housekeeping, etc.
Fixed costs do not vary (for a given period) with changes in the test volume, whereas variable costs change proportionally with changes in test volume. The cost of a testing instrument is fixed; reagents, controls, and disposable supplies constitute variable costs. Table 1 illustrates the various cost categories.
Table 1. Cost Categories.
| Cost Category | Definition | Examples |
| Direct costs | Attributed to an individual test | Reagents, personnel performing tests, calibrators, proficiency testing |
| Indirect costs | Not attributed to an individual test | Housekeeping, electrical use, building maintenance, HVAC |
| Fixed costs | Constant and not subject to test volume | Test instrument, accreditation, non-testing personnel, i.e., managers and administrative assistants |
| Variable costs | Changes based on test volume | Reagents and disposables |
Labor for testing may be fixed or variable, but it is generally considered a fixed cost unless new personnel are hired or overtime is required to perform the testing. For example, if salaried personnel are hired to do the entire laboratory testing during a specific period (e.g., an 8-hour day), their contribution to performing that specific test becomes fixed.
