Often blood from children is drawn in the same big tubes used for adults. I applaud parents, nurses, or phlebotomists acting as advocates for children when large-volume draws are ordered, to be sure that the amount requested is carefully considered. In general, it is preferable to withdraw the smallest amount that will still allow the best medical care for the child. One way to do this is to ask that the blood be drawn in pediatric (not adult) tubes where possible, using something we call micro-sampling techniques – equipment designed to use the smallest amount necessary for each test. For example, in healthy newborns, we use a heel stick to obtain just a very small amount of blood- but it is sufficient to run the medically necessary tests in the first few days of an infant’s life. However, for some labs venipuncture is required and therefore being aware of the limits of blood draws in the pediatric population is important,
Excessive phlebotomy reduction (EPR) techniques are being researched and put to use in many hospitals. These include using techniques such as heel and finger sticks for labs (if possible), reducing blood waste, reducing the frequency of blood draws in the hospital, and using smaller tubes for pediatric populations.
To parents, I suggest asking to be sure it is truly necessary if someone suggests taking more than 1 ml of blood per pound of your child’s weight (or a maximum of 30 ml for larger children). Thirty ml is equivalent to 1 ounce.
I gave a general rule of thumb I use as an outside limit for blood draws, because at these levels of blood loss there can be measurable health consequences. Blood draws in infants and children should not exceed 5% of their total blood volume in any 24-hour period, unless medically necessary. This is a generous upper limit. Ideally, it should be less than 3% of the total blood volume (many guidelines use a 2.5% limit for any one blood draw), and where possible, micro-sampling techniques to reduce the amount further are preferred. Blood draws in infants and children should not exceed 10% (and some guidelines even use 5%) of the total blood volume in any one-month period, unless medically necessary.
The total blood volume can be estimated from the age and weight of the child. As a rough estimate, for pre-term babies, the amount of blood is about 85-90 ml per kilogram of body weight. For term newborns, it is about 80 ml per kg. For older babies, 1 to 12 months of age, estimate 75 ml per kg. For toddlers, up to age 3 estimate 70 ml per kg. And for older children and teens, 65 ml per kg is a reasonable estimate.
These are general guidelines, and the individual medical situation should be taken into account. But think twice whenever adult techniques or equipment are suggested for children. It is widely accepted that whenever possible a person trained in pediatric phlebotomy should perform the blood draws in order to minimize blood loss or multiple attempts at extracting blood.
To put these numbers in perspective, I have attached the guidelines from several different hospitals and labs. As you will see, there is not universal agreement on the precise numbers, but there is a general awareness that it is best to minimize blood loss, and the numbers used at different centers fall within a narrow range.
In most hospitals, conservative guidelines are used and special permissions are required to use upper limits (taking more than 5% of total blood volume at once)
|Body wt in kg||Max drawn in one blood draw||Maximum drawn in a 30 day period|
|2.5% of total blood volume||5% of total blood volume|
|1 kg||2.5 ml||5.0 ml|
|2 kg||4.5 ml||9.0 ml|
|3 kg||6 ml||12 ml|
|4 kg||8 ml||16 ml|
|5 kg||10 ml||20 ml|
|6 kg||12 ml||24 ml|
|7 kg||14 ml||28 ml|
|8 kg||16 ml||32 ml|
|9 kg||18 ml||36 ml|
|10 kg||20 ml||40 ml|
|11 thru 15 kg||22 – 30 ml||44 – 60 ml|
|16 thru 20 kg||32 – 40 ml||64 – 80 ml|
|21 thru 25 kg||42 – 50 ml||84 – 100 ml|
|26 thru 30 kg||52 – 60 ml||104 – 120 ml|
|31 thru 35 kg||62 – 70 ml||124 – 140 ml|
|36 thru 40 kg||72 – 80 ml||144 – 160 ml|
|41 thru 45 kg||82 – 90 ml||164 – 180 ml|
|46 thru 50 kg||92 – 100 ml||184 – 200 ml|
|Greater than 50 kg||100 ml||200 ml|
At Harvard’s Mass General they use the following guidelines for research purposes:
The Guidelines of the NIH Clinical Center for research purposes are:
For pediatric patients, no more than 3 ml/kg. may be taken for research purposes in a single draw, and no more than 7 ml./kg. may be drawn over any six-week period. Investigators should consider further limiting blood drawing in patients with anemia or low cardiac output.
In instances of clinical needs, phlebotomy in excess of the above limits may be permitted.
At UCLA they use:
Howie SR. Blood sample volumes in child health research: review of safe limits. Bull World Health Organ. 2011;89(1):46-53.
Steffen, K, et al. Controlling Phlebotomy Volume Diminishes PICU transfusion: Implementation Processes and Impact. Pediatrics 2017; 140 (2):