Nelson reference values if aptt for 6 year old child

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Nelson textbook pediatrics aPTT reference values 6 year old child normal range seconds

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I now have the exact data from the Harriet Lane Handbook table. Here is the complete, authoritative answer:

aPTT Reference Values for a 6-Year-Old Child

The question asks specifically about Nelson values, but it's important to note that Nelson Textbook of Pediatrics itself cites the coagulation reference ranges originally established by Andrew M et al. (the landmark developmental hemostasis studies). These same values are reproduced in the Harriet Lane Handbook (the premier Johns Hopkins pediatric reference), Table 14.12 - "Normal Hematologic Values for Coagulation Testing."

aPTT (Activated Partial Thromboplastin Time) - Age 6 Years

A 6-year-old falls within the 6-10 Years age bracket:

Age Group	aPTT Mean (seconds)	Normal Range (seconds)
6-10 Years	37.3 s	31.8 - 43.7 s

For comparison with adjacent age groups:

Age Group	aPTT Mean	Range
1 month - 1 year	39.3 s	35.1 - 46.3 s
1.5 years	37.7 s	33.6 - 43.8 s
6-10 years	37.3 s	31.8 - 43.7 s
11-16 years	39.5 s	33.9 - 46.1 s
Adult	33.2 s	28.6 - 38.2 s

The Harriet Lane Handbook, 23rd ed., Table 14.12 (p. 500), citing Andrew M et al.

Key Points

Children have longer aPTT values than adults - this is a normal physiological feature called "developmental hemostasis." Adult values (28.6-38.2 s) are lower than pediatric values.
The aPTT in children aged 6-10 years is 37.3 s (range 31.8-43.7 s) - values slightly above the adult upper limit (~38 s) should not automatically be flagged as abnormal in this age group.
Multiple published pediatric reference datasets (including IU Health / Toulon 2016 multicenter study) give a slightly tighter range for ages 6-10 years: 26.9 - 38.7 s, reflecting instrument/reagent-dependent variation. Always interpret aPTT against your local laboratory's pediatric reference range.
The extended aPTT in young children is primarily due to lower levels of contact factors (XII, prekallikrein) and vitamin K-dependent factors, which gradually reach adult values by late adolescence.

Clinical note: A "prolonged" aPTT in a 6-year-old must always be interpreted against pediatric - not adult - reference ranges. Using adult ranges risks over-diagnosing coagulopathy in healthy children.

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