Table 1.

Paediatric blood sampling procedures that may be employed in pharmacokinetic studies or clinical trials

Method of blood sampling	Advantages	Disadvantages	Preferred age group(s)	Comments
Sampling from an indwelling arterial catheter or central venous line	No need for separate invasive procedures (that would require additional needles). If such a line is already in place for clinical purposes, the risks associated with blood sampling are limited.	Potential infection risk from additional accessing of the line; blood loss due to inappropriate line handling; premature loss of the line. Sometimes additional blood volume (dead-space) needed to clear the line of other infusion fluids.	Method feasible in all age groups.	Some centres return this dead-space volume directly after sampling, while others consider it unhygienic, dependent on the structure of the specific line system used and local practice. Method commonly used in intensive care settings.
Cannulation-based venepuncture	Different options are possible, either multiple or single use of an intravenous cannula. With multiple use of a single intravenous cannula, the burden of the insertion is reduced to only once.	Often multiple attempts are needed before successful peripheral cannulation. The blood flow may be too slow and blood may clot in the cannula system, even when intermittent or continuous saline flushes are instilled in the cannula.	For smaller children, open collection systems are more appropriate.	In very small children, repeated sampling from one cannula may also be difficult.
Venepuncture (without cannulation)—(1) vacuum systems	Several methods can be used: in older children, simple vacuum systems in large veins are most frequently employed. Discomfort can be reduced by appropriate use of local anaesthetic cream.	Usually involves study-specific invasive procedure. Less suitable for younger children. Not suitable for some children who have experienced very high numbers of routine blood tests (eg, in oncology).	Preferred in older children. In younger infants and neonates, these methods are less practical or even unfeasible, as the size of the vein means the vacuum will collapse the vessel so no blood can be taken.	Culturally specific factors can be important: parents in some countries are happy for their children to have extra blood tests at any age, whereas other cultures can be very against the invasiveness of the method.
Venepuncture—(2) non-vacuum methods: for example, the use of syringe needles or the needle from a Vacutainer system	These needles are easier to insert and manipulate in small veins than intravenous cannulae and have less problems with blood clotting, due to the large bore size (syringe needles) and heparin coating (Vacutainer needles).	This method needs practice by specifically trained personnel.	Preferable for younger children (in whom vacuum-based systems and/or cannulation may be difficult).	In all these non-vacuum methods, blood needs to drop in opened tubes. In general blood samples up to 5 mL per occasion can be taken, before the blood starts to clot, but it is widely variable per patient and becomes less with decreasing age.
Capillary sampling: heel prick or finger prick	The advantage of finger/heel pricks is that they can be easily taught to parents and children. This method can be less invasive and painful than venepuncture or intravenous cannulation (although this is debatable).	Capillary sampling is not always comfortable: studies have shown that venepuncture is preferred over finger pricks in older children. Also, to obtain adequate blood volumes, repeated punctures may be needed, and also continued pressing of the foot or fingers, which is uncomfortable.	The heel prick method is often preferred in neonates when normal venepuncture and cannulation are not required for clinical reasons.	Since this can be taught to children or their carers, they may be able to collect blood samples at home, in connection with dried blood spot analysis.