Clinical audit of plasma methylmalonic acid (MMA) requests following publication of NICE guidelines on Vitamin B12 deficiency in over 16s

Abstract

Background

Vitamin B12 deficiency can cause anaemia, fatigue, and neurological sequelae. Total B12 assays may not be reflective of tissue B12. Methylmalonic acid (MMA) can assess tissue B12 more accurately. NICE published clinical guidelines on Vitamin B12 deficiency in adults in 2024. They outlined MMA testing in two scenarios: in patients where nitrous oxide use is possible or who have an indeterminate total B12 result (180–350 ng/L) alongside symptoms or signs of B12 deficiency. MMA testing is costly, not readily available, and time consuming, so increased use will have implications.

Methods

This is a Case note review of patients who had MMA requested one year prior to and one year post-NICE NG239 publication. Audit standards followed were NG239 indications for MMA testing.

Results

In the year after NG239, MMA testing increased by 96% (57 to 112). Whilst only 47% would have meet NG239 testing criteria in the prior group, this increased to 79% in the post group. More were diagnosed with B12 deficiency (16% prior and 21% post), and more commenced on B12 treatment (14% prior and 19% after). Comparing simultaneous total B12 and MMA results suggests an increase in the upper reference interval of the indeterminate range to 375 ng/L could be considered.

Conclusions

Demand for MMA testing almost doubled after NG239 was published, though requests appeared much more appropriate. Whilst laboratory costs increased, there may have been savings elsewhere in the system. Further analysis would be required to review the extent of these healthcare savings in practice.