Lorde, NathanPratt, GuyGeberhiwot, TarekegnAyuk, JohnGittoes, Neil2025-09-022025-09-022025-07-31Lorde N, Pratt G, Geberhiwot T, Ayuk J, Gittoes N. Paraprotein-induced spurious hypercalcaemia: diagnostic pitfalls in two cases. Eur J Endocrinol. 2025 Jul 31;193(2):K1-K4. doi: 10.1093/ejendo/lvaf151.0804-46431479-683X10.1093/ejendo/lvaf15140712044821363340712044https://westmid.openrepository.com/handle/20.500.14200/8360This brief report describes 2 cases in which paraprotein caused spurious biochemistry results. In both cases standard laboratory measurements of calcium indicated the patients were hypercalcaemic and had significantly raised Vitamin D concentrations in serum. However, use of alternative measurements of calcium and vitamin D showed that these results were spurious. Clinicians looking after patients with significant paraprotein concentrations or other significant protein abnormalities should be aware of the possibility of assay interference when reviewing their biochemistry results. This awareness can be vital in avoiding unnecessary investigations or treatments, thus not only saving resources but also protecting patients from harm that may be caused by inappropriate therapies.en© The Author(s) 2025. Published by Oxford University Press on behalf of European Society of Endocrinology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.Clinical pathologyHaematologyBiochemistryEndocrinologyReport