Establishment of a reference interval for calculated globulin on the Roche platform

BackgroundCalculated globulin, based on direct measurement of total protein and albumin, can be a useful addition to the routinely requested liver profile. However, a reference interval, established using CLSI EP28-A3c recommended direct methods, is lacking for the commonly used Roche method [albumin bromocresol green (BCG), total protein (biuret)].MethodsThis direct reference interval study was carried out between January and March 2024, based on Roche methods for total protein (biuret) and albumin (BCG). Reference individuals comprised 310 highly selected adults from primary care, ages ranging from 16 to 89 years. The CLSI guideline, EP28-A3c, was strictly followed. We also established a reference interval using an indirect approach for comparative purposes, using results from 8466 unselected primary care patients.ResultsThe reference interval for calculated globulin established using direct sampling techniques was 23 g/L (90% CI 22-24 g/L) - 35 g/L (90% CI 34-36 g/L). The reference interval established using indirect sampling techniques in a much larger unselected reference group was 22 g/L (90% CI 22-22 g/L) - 37 g/L (90% CI 37-37 g/L).ConclusionsWe have established a reference interval for calculated globulin, specific to the Roche total protein and BCG albumin methods. This will be a useful tool for other laboratories which use the Roche BCG albumin method, allowing adoption of this reference interval with a simple transference study. The range was a little broader but not materially altered (medians exactly the same) when strict exclusion criteria were removed and also when using a data mining approach, which resulted in a 27-fold larger reference group.