Clinical validation of an innovative dried whole-blood spot method to quantify simultaneously vancomycin and creatinine in adult patients

Background: 

A drawback of vancomycin use is the need for therapeutic drug monitoring and renal function monitoring. Traditional blood sampling involves drawing blood through a venepuncture. An alternative method, dried blood spot (DBS) sampling allows for self-sampling at home.

Objectives: 

To clinically validate a DBS method for simultaneous monitoring of vancomycin and creatinine. 

Methods: 

Hospitalized adults treated with intravenous vancomycin were included (trial registration NCT05257070). Blood sampling consisted of one venepuncture and one finger prick. Whole-blood DBS samples from patients were obtained by applying one drop of whole blood onto Whatman 903 filtrate paper. Bland–Altman analyses were used to assess the agreement and bias between the two measurements. Patients were asked to state their preferences for one of the two sampling methods. 

Results: 

The study involved a final analysis of 39 patient samples for the clinical validation of vancomycin and 46 patient samples for the clinical validation of creatinine. The difference between plasma and DBS concentrations was ≤20% for 77% of the vancomycin samples, the mean bias was −0.1379% (95% limit of agreement −5.899–5.623). The difference between plasma and DBS concentrations was ≤20% for 89% of the creatinine samples, the mean bias was 2.656% (95% limit of agreement −26.16–31.47). Most patients (18 out of 31) preferred a finger prick over a venepuncture and 12 patients indicated no preference. 

Conclusions: 

This is the first study that successfully clinically validated a DBS sampling method for simultaneous measurement of vancomycin and creatinine, allowing for direct use in (outpatient) practice.