A comparison of cost for mycobacterial load determination in research laboratories

A Pooran, R Meldau, K Dheda, R N van Zyl-Smit

Abstract


Background. Mycobacterial load determination is a critical quantitative measure needed in many clinical and research laboratory studies and selection depends on several factors including sensitivity, dynamic range and turnaround time. However, there are no data about cost, which is an important selection determinant. We therefore performed a cost analysis of five quantitative mycobacterial load assays.

Methods. The costs of five mycobacterial quantification techniques were compared in a hypothetical single experiment (control and intervention) performed in triplicate. Assays evaluated were: mycobacterial colony-forming units (MCFU) using 7H10-Middlebrook solid media, automated liquid culture (BACTEC-MGIT-960), [3H]-uracil incorporation assays, luciferase-reporter construct bioluminescence, and quantitative polymerase chain reaction (PCR) (Xpert-MTB/RIF) using serial dilutions of Mycobacterium tuberculosis. Costs associated with consumables, equipment and personnel were included and expressed in 2015 South African rands and US dollars.

Results. The least costly technique was the luminescence reporter construct assay (R85.68/$6.72) whereas the most expensive technique was the Xpert MTB/RIF PCR (R388.02/$30.42). The high cost of the PCR assay was mainly attributable to the costly Xpert MTB/RIF cartridges. Although the MCFU by solid culture had a similar cost compared with uracil incorporation and Xpert MTB/RIF, the purchase price of the equipment required to perform the latter assays was ~2 - 10 times higher.

Conclusion. Taking into consideration the turnaround time, capital costs, discriminatory ability, the running costs (excluding staff) of the luminescence reporter assay are the lowest. Where time to result is critical, more expensive techniques such as the Xpert MTB/RIF should be used. In a clinical setting where automated culture and Xpert are routinely performed, quantitative load from time to positivity and cycle thresholds will provide extra data without additional cost.


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DOI: http://dx.doi.org/10.7196/SARJ.2015.v21i3.22

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