Measurement of blood serum cyclosporine levels using capillary "fingerstick" sampling: a validation study

Autonomic, endocrine, and psychological stress responses to different forms of blood draw

Background

Although fingerstick is often favorably compared to venipuncture as a less invasive method of drawing blood for clinical labs, there is little empirical research that compares physical and psychological stress responses to fingerstick vs. venipuncture (blood draw using a needle in the arm) within the same person.

Methods and findings

We assessed changes in cortisol (a stress hormone), heart rate variability (a marker of autonomic stress), and psychological stress in 40 healthy women who completed both venipuncture and fingerstick. Contrary to our predictions, there was a significant decline in cortisol across conditions, with greater decline from pre- to post-draw in response to venipuncture than fingerstick. There were similar patterns of rise and fall in heart rate variability in both types of blood draw, suggestive of mild vasovagal responses. Psychological measures of stress (such as negative emotion and perceived stress) were generally stronger predictors of participant’s reported pain and blood draw preferences than physical stress measures.

Conclusions

These findings challenge the characterization of fingerstick as necessarily “less invasive” than venipuncture, as participant’s stress responses to fingerstick were equivalent to (and for some measures greater than) their response to venipuncture. Heart rate variability response to fingerstick significantly predicted that individual’s vasovagal-like responses to venipuncture, suggesting that measuring heart rate variability during pre-donation hemoglobin testing may identify donors at risk for adverse events during venipuncture.

Can finger-prick sampling replace venous sampling to determine the pharmacokinetic profile of oral paracetamol?

WHAT IS ALREADY KNOWN ABOUT THE SUBJECT: Finger-prick blood samples are increasingly used for the clinical and biomedical measurement of drugs and endogenous substance concentration. The use of different sampling sites can give rise to different drug concentration measurements.

WHAT THIS STUDY ADDS

During the absorption phase, the paracetamol concentration in finger-prick blood samples is significantly greater than that in venous blood samples, following oral administration. Finger-prick and venous blood samples will result in equivalent pharmacokinetic parameters of oral paracetamol only after distribution equilibrium is attained. The drive to increase the availability of paediatric pharmacokinetic data with minimum blood loss has led to the development of micro-sampling techniques. However studies have suggested that pharmacokinetic data from venous or capillary blood samples may not be directly comparable.

AIM

The aim of this study was to determine whether paracetamol demonstrates concentration differences between finger-prick and venous blood samples.

METHODS

Paired finger-prick and venous blood samples were taken at 0, 15, 30 and 60 min following 1 g oral paracetamol, from 12 male adult subjects. Paracetamol concentration was determined using HPLC and UV detection with a LLOQ of 2200 pg on column. Intra-assay coefficient of variation for paracetamol at the LLOQ was 3%.

RESULTS

At 15, 30, and 60 min post dose the median finger-prick paracetamol concentration was 349%, 72%, and 9.3% greater than the equivalent venous concentrations, respectively. Regression analysis confirmed a significant relationship between finger-prick and venous paracetamol concentrations at 15 min (r(2) = 0.81, P = 0.006), at 30 min (r(2) = 0.82, P < 0.0001) and at 60 min (r(2) = 0.87, P < 0.0001) post dose. The regression equation for venous and finger-prick blood concentrations at 15, 30 and 60 min post dose were Venous(15) = Finger(15) - 3.4, Venous(30) = Finger(30) - 3.4 and Venous(60) = 0.68 Finger(60) + 3.06, respectively.

CONCLUSIONS

Paracetamol demonstrates an arteriovenous difference in concentration, and the use of finger-prick samples may give rise to results which differ from those obtained with traditional venous sampling especially during the first 1 h following drug ingestion.