Cost Effectiveness & Underpowered Studies

A recent study (ALT Ma et al. J Pediatr 2016; 179: 216-8) reaches a conclusion that questions the cost-effectiveness of pretreatment TPMT activity in pediatric patients. In my opinion, this retrospective study is ridiculous. Here’s why:

The authors examined thiopurine transmethyltransferase (TPMT level) in 228 children before starting a thiopurine. They found the following:

  • Only 2 patients experienced mild neutropenia
  • 12% of their cohort had intermediate activity and 88% normal TPMT activity

I agree with their conclusion that routine blood tests are needed following institution of thiopurines, I think stating that “from an economic point of view –the cost for testing TPMT enzyme activity was high without major clinical benefit” cannot be made with such a small study.  Deficient TPMT activity occurs in about 1 in 300.  If a single patient develops bone marrow suppression due to a thiopurine medication, this can lead to a horrific and prolonged hospitalization.  The cost of such a hospitalization, both economically and emotionally, is enormous.

My take: If I were taking a thiopurine, I would want to know if I metabolized this medication at a slower rate and was at increased risk for bone marrow suppression.  My hunch is the authors would not forgo checking a TPMT level on themselves despite their study’s conclusion, particularly if they have ever witnessed a patient with thiopurine-induced bone marrow suppression.

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