TB diagnostic tests: how do we figure out their costs?

Figures & data

Figure 1. Planning for cost analysis in TB laboratory diagnostics.

This diagram provides a step by step plan for cost analysis in evaluating TB diagnostic tests in various study settings. Steps 3, 4 and 5 should be undertaken for all the methods evaluated and relevant sub-procedures and repeated to capture data variations caused by specimen loads (and/or specimen batch size). In step 7, the investigator should consult laboratory experts regarding diagnostic workflow to reflect local laboratory practice in combining procedure unit costs.

Figure 2. Example of diagnostic workflow of a TB culture laboratory with molecular diagnostic capacity.

When first planning for a costing study, evaluating diagnostic workflow is essential in capturing all aspects of laboratory activities that need to be evaluated for costs. Shown is a generalized workflow observed in a laboratory where molecular testing for MDR-TB using a line probe assay is being evaluated against the conventional culture method using LJ in a demonstration study. Actual workflow at different laboratories may vary.

CPC: Cetylpyridinium chloride; DST: Drug susceptibility testing; FM: Fluorescent microscopy; LJ: Löwenstein Jensen; MDR: Multidrug resistance; NALC: N-acetyl-L-cysteine; Z/N: Ziehl-Neelsen.

Figure 3. Component of unit cost figure of a laboratory procedure.

Costs associated with training/QA/QC are assessed independently as per activity cost and allocated into average unit cost based on staff timing associated with the relevant laboratory procedure. For example, test specific training/QA/QC (e.g., culture and molecular testing hands-on training) should be allocated only into test specific unit cost, where as period QA/QC for general laboratory activities should be allocated into all of the laboratory procedures/activities calculated for unit cost.

QA: Quality assurance; QC: Quality control.

Table 1. Summary of costing methodology utilized in various cost and cost–effectiveness studies evaluating TB diagnostics.

Focus of the study	Diagnostic systems evaluated	How was the cost of the diagnostic system evaluated?	Ref.
Comprehensive (performance and cost) comparison of ZN and FM in resource-poor setting	ZN and FM	Quoted separately as laboratory costs stratified by labor, investment (equipment), and running costs based on 50 ZN and 80 FM slides per day	[18]
Complete economic assessment of laboratory costs associated with ZN and FM in Thailand	ZN and FM	Comprehensive assessment of all economic costs (overhead, building, equipment, staff, chemicals, reagents and consumables) associated with each diagnostic tool based on direct observation and time analysis from a health services perspective	[19]
Costs and cost–effectiveness of use of liquid media culture in Zambia	LJ (home-made vs commercially purchased) and MGIT (automated vs manual)	Reported as culture specific (consumables, equipment and staff) and overhead (e.g., building, electricity and transportation) costs evaluating all costs associated with the laboratory only based on observation and review of expenditure logs	[24]
Cost–effectiveness of IFN-γ release assays in screening TB suspects and contacts in high-income countries	Tuberculin skin test, chest x-ray, QuantiFERON^®-TB Gold, T-SPOT.TB^®	Manufacturers’ unit pricing and estimated cost of laboratory staff for relevant test	[20–22]
Cost and cost–effectiveness of rapid alternative diagnostic methods in screening for MDR-TB in Peru	Indirect LJ, direct LJ, INNO-LiPA, FASTPlaque-Response, MTT assay	Comprehensive assessment from a health services perspective of direct and indirect laboratory costs associated with each respective diagnostic method based on a time observation and ‘ingredients’ approach	[25]
Cost–effectiveness of molecular based diagnostic method for TB used routinely on smear-positive specimens	AMPLICOR Mycobacterium tuberculosis and Amplified Mycobacterium tuberculosis Direct (MTD) test	Manufacturers’ unit pricing, accounting cost figures and estimated cost of laboratory staff for relevant test	[23]

DST: Drug susceptibility testing; FM: Fluorescent microscopy; LJ: Löwenstein–Jensen; MDR: Multidrug resisant; MGIT: Mycobacterium growth indicator tube; MTT: 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole; ZN: Ziehl-Neelsen.

Table 2. Cost data elements for cost analysis of TB diagnostics and suggested data sources.

Data element	Cost items	Suggested sources of data
Physical infrastructure	Construction	Construction contractors/government estates and building planning office/recent laboratory construction budget
	Maintenance contracts for all laboratory equipment requiring periodic maintenance	Laboratory financial records/laboratory or hospital accounts office/service contractors
Chemicals and reagents, and consumables	All types of chemicals and reagents utilized for diagnostic methods evaluated	Laboratory financial records/manufacturer catalog (must include all costs associated with procurement, usually at 25% of the catalog price)
	All types of general laboratory consumables (e.g., latex gloves, micropipette tips)	Laboratory financial records/manufacturer catalog (must include shipping costs)
Human resources	Laboratory staff salaries	Government salary scale/laboratory or hospital accounts office
	Laboratory staff allowances and benefits	Government salary scale/laboratory or hospital accounts office
	Staff training off-site	Laboratory records/interview
Training and quality assurance	Orientation training for new staff	Laboratory staff records
	External QA/QC for various laboratory diagnostic activities	Pricing/cost available through laboratory/hospital accounts office. List of QA/QC programs can be found in the general SOP
	Internal QA/QC	Cost can be evaluated as part of the general cost analysis using ‘ingredients’ approach. The full list of internal QA/QC procedures can be found in the general SOP
Specimen transport	Cost of a vehicle used for specimen transport – evaluated as purchased ‘new’	Accounting office/autodealer
	Average distance traveled – annual figure	List of locations referring specimens to the laboratory
	Average driver salary	Accounting office
	Quantity of fuel used	Accounting office
	Fuel price	General market research, accounting office
	Insurance of vehicle	Accounting office
	Other consumables used in specimen transport	Accounting office

QA: Quality assurance; QC: Quality control; SOP: Standard operating procedure.

Table 3. Cost parameters (and examples) based on cost and cost–effectiveness analysis in TB diagnostics.

Perspectives of economic evaluation in health interventions
Provider perspective	Examples
Direct costs associated with laboratory and other types of diagnostic services	Detailed cost of diagnostic services, laboratory staff costs, consumables costs and overhead costs (details presented in cost analysis section)
Direct costs associated with medical services	Detailed cost on hospital admission costs and treatment costs
Patient perspective
Direct costs incurred by patient	All types of out-of-pocket payments for drugs and other types of treatment following diagnosis, cost of travel and income transfer payments
Time costs to patients and their families	Patient’s time spent for travel and receiving treatment, lost time (salary) at work by patient and family
Productivity	Lost productivity due to illness resulting in reduced working capacity, costs to employer to hire and train replacement worker for patient

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