How Much Blood is too Much Guideline

How Much Blood is too Much Guideline

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 blood draws are ordered, to be sure that the amount of blood requested is carefully considered. In general it is preferable to withdraw the smallest amount of blood 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 least amount of blood necessary for each test.

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, and where possible, micro-sampling techniques to reduce the amount further are preferred. Blood draws in infants and children should not exceed 10% 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 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.

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.

Alliance Laboratory Services uses the following table:

Maximum Amounts of Blood to be Drawn From Patients Younger than 14 Years

Patient’s Weight Pounds Patient’s Weight Kilograms (approx.) Maximum Amount to be drawn at any one time (mL) Maximum Amount of blood –cumulative to be drawn during a given hospital stay (1 month or less-mL)
6-8 2.7-3.6 2.5 23
8-10 3.6-4.5 3.5 30
10-15 4.5-6.8 5 40
16-20 7.3-9.1 10 60
21-25 9.5-11.4 10 70
26-30 11.8-13.6 10 80
31-35 14.1-15.9 10 100
36-40 16.4-18.2 10 130
41-45 18.6-20.5 20 140
46-50 20.9-22.7 20 160
51-55 23.2-25.0 20 180
56-60 25.5-27.3 20 200
61-65 27.7-29.5 25 220
66-70 30.0-31.8 30 240
71-75 32.3-34.1 30 250
76-80 34.5-36.4 30 270
81-85 36.8-38.6 30 290
86-90 39.1-40.9 30 310
91-95 41.4-43.2 30 330
96-100 43.6-45.5 30 350


At Harvard’s Mass General they use the following guidelines when the blood is taken solely for research purposes:

  • Blood volume taken from children must be less than 3 cc/kg body weight per 8 week period. In studies where the direct benefit far outweighs this volume restriction, a full protocol must be submitted for review of the full committee, and the following guidelines will apply:
    • If more than 3 cc/kg body weight per 8 week period is required and justified by the potential benefits, up to 9 cc venous blood/kg body weight/8 week period may be considered in older children (e.g., not neonates, toddlers, etc.), with the latter figure being the absolute upper limit.
    • Any child involved in a study involving removal of venous blood in the range of 3-9 cc/kg body weight per 8 week period should be placed on iron supplementation therapy. It is recommended that a dose of 30 mg ferrous sulfate/kg/day in 3 divided doses be given. Such therapy should continue for at least 8 weeks and should be monitored by hemoglobin measurements.

The Guidelines of the NIH Clinical Center, for blood drawn for research purposes are:

For pediatric patients, no more than 3 ml/kg. may be drawn for research purposes in a single blood withdrawal, 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:

  1. No more than 2.5% of total blood volume may be drawn solely for research purposes (no benefit to the subject) within a 24-hour period. This is generally 2 ml/kg.
  2. No more than 5% of total blood volume may be drawn solely for research purposes (no benefit to the subject) within a 30-day period. This is generally 4 ml/kg.
  3. If the investigator requests blood in excess of this amount, he/she must provide a detailed justification for this, and describe what safeguards are in place to protect the subject from undue risk.

Dr. Alan Greene

Dr. Greene is the founder of (cited by the AMA as “the pioneer physician Web site”), a practicing pediatrician, father of four, & author of Raising Baby Green & Feeding Baby Green. He appears frequently in the media including such venues as the The New York Times, the TODAY Show, Good Morning America, & the Dr. Oz Show.

  1. zmm912714

    Help! It’s horrific! My period is every 15-20 days sometimes 2 times a month. I lose a cup of blood every 2-3 hours and everytime I use the restroom in a day of my menstral cycle. I use the restroom 7-9 times a day.

    • Oh, my. What does your doctor say? This seems like it’s way out of the norm.

      (Note: I’m not a doctor, just a woman, mom, and caring person)

  2. sandra olson

    a 4 month old child, born 5 weeks premature, weighing 4 11 at birth and 4 1 when left hospital, would be I am guessing no more then 7 or 8 lbs at 4 months of age,, in 1994, how much blood would have been required, to have run both hla testing and dna testing, and would such an amount have been safe to take from such a small infant.

  3. PHIL

    Great, no answers from anybody!

  4. imran khan

    My child is 2 years old today.he had 6 pont of blood taken 11 kg weaght only. And he does not take food. So he is very week. Please explan this to me i feel like bad now

  5. Eva

    Hi,I went for GYN docter today,they drawm me 10 blood samples at one time,10 big tubes…is this normal and necessary..usually only takes 1 tube

  6. Monica Owen

    My baby is four months old today she had 13 mls of blood taken she is 6.9kg or 15lb.6oz ,dr delatorie at cooks childrens in ft worth tx ordered for CAH testing this is the second time he has ordered this exact amount last time she was only 8 lbs is this safe for her she is realy sluggish and thats not normal for she is usualy a verry bubbly baby please explain this to me i feel like i just keep getting the run around has anyone else had this experience

    • sandra olson

      did you get a reply on this safe amount for about an 8 lb baby to have taken? I was wondering as well


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