Although the active pharmaceutical ingredient remains constant, the excipients used will vary according to the manufacturer. This case report is of spuriously raised serum creatinine due to an excipient in one particular intravenous dexamethasone formulation. A patient had three serum creatinine measurements of 102, 369 and 91 μmol/L over a four-hour period. The second result was believed to be spurious and appropriate investigations were instigated. The patient had received dexamethasone intravenously between the first and second blood samples. This was administered as a bolus via a cannula in the dorsum of the hand, and the blood sample was taken by venepuncture of the antecubital fossa of the same arm approximately five minutes later. The dexamethasone used (Hospira UK Ltd) contained creatinine at a concentration of 70,720 μmol/L, with a total of 170 μmol of creatinine given to the patient. Assuming a volume of distribution of 40 L in a 70-kg man, an increase in serum creatinine of 4-5 μmol/L would be expected once equilibrated. It is thought that the serum creatinine result observed was a consequence of the creatinine excipient in the dexamethasone not having completely distributed throughout the body and still being at relatively high concentrations within the limb into which it had been administered. Intravenous dexamethasone can lead to spurious creatinine results, not due to analytical interference but rather the analytically correct measurement of creatinine added as an excipient. This case clearly demonstrates the impact preanalytical factors can have on the accuracy of results.