Aims: The National Pathology Alliance benchmarking review has completed five years of data collection and analysis of the workload and organisation of haematology laboratories in the UK. This study analyses variation in practice in how laboratories respond to a request to determine whether or not a patient has folate deficiency. Methods: A three year analysis of workload data on the number of serum/plasma folate and red cell folate assays performed on an annual basis for the period 1 April 1999 to 31 March 2002. Results: Three diagnostic testing strategies were found, namely: serum/plasma folate only, red cell folate only, and both serum/plasma folate and red cell folate. Conclusion: Evidence from the literature indicates that serum folate measurements provide equivalent information to red cell folate measurements when attempting to determine whether folate deficiency is present. There seems to be no basis for the routine testing of all samples for serum/plasma folate and a red cell folate.T he National Pathology Alliance benchmarking review has now completed five annual cycles of data collection and analysis of the workload and organisation of haematology departments in the UK.1 When the benchmarking study was started there was no agreed national definition of what constituted a test and a request in haematology and blood transfusion. Therefore, a major part of the first two years' reports was to establish a national definition of tests and requests in haematology and blood transfusion, because without this no comparative assessment of a department's performance can be undertaken. In haematology, this has been achieved, with over 95% of departments now using the standard definition of tests and requests when completing the workload section of the questionnaire. Over the past two years, increasing attention has focused on the variation in diagnostic testing strategies used in different laboratories. This report analyses variation in practice in how laboratories respond to a clinical request to determine whether or not a patient has folate deficiency.''We analysed the variation in practice of different diagnostic testing strategies that laboratories have established to determine whether or not a patient is deficient in folate'' Folate values can be measured using either a serum/plasma folate or a red cell folate assay. National guidelines indicate that a negative folate balance seen in hospital patients can result in a low serum folate value without folate deficiency.2 Therefore, low red cell folate, thought to indicate tissue deficiency, may be more important than a low serum folate in the diagnosis of folate deficiency. However, no references were given in these guidelines to substantiate this view.Therefore, we analysed the variation in practice of different diagnostic testing strategies that laboratories have established to determine whether or not a patient is deficient in folate. We have also reviewed the literature to determine the appropriate diagnostic testing strategy in this situation. METHODSThe metho...