# Very low mapping rate of Hummann v4alpha

**URL:** <https://forum.biobakery.org/t/very-low-mapping-rate-of-hummann-v4alpha/8534>\
**Category:** HUMAnN\
**Created:** [September 29, 2025, 10:05am UTC](https://forum.biobakery.org/t/very-low-mapping-rate-of-hummann-v4alpha/8534 "2025-09-29T10:05:20Z")\
**Posts on this page:** 1\
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**Author:** ![gillian\_McClennen](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.biobakery.org/gillian_mcclennen/32/3352_2.png) [@gillian\_McClennen](https://forum.biobakery.org/u/gillian_McClennen)\
**Post date:** [February 23, 2026, 2:38pm UTC](https://forum.biobakery.org/t/very-low-mapping-rate-of-hummann-v4alpha/8534/3 "2026-02-23T14:38:22Z")

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Hi @SilasK,

Did you check this forum?: [READS\_UNMAPPED Is Not Presented in CPM Format - #2 by franzosa](https://forum.biobakery.org/t/reads-unmapped-is-not-presented-in-cpm-format/8490/2)

I also was really scared for a second because I’m using HUMAnNv4.0.0.a, and when I initially normalized by relative abundance the mapping rate in my uniref genefamilies output was extremely low. However, in that forum page they discuss that, in HUMAnN4 specifically, the units of the unmapped\_reads in the genefamilies output are in raw reads, whereas the rest of the genes are normalized to copies per million (CPM) units. Because the raw reads number can be much greater than 1 million, it can look like there is a much lower mapping rate than there truly is. You can look in the log file for the true mapping rate of the genefamilies output.

Hope this helps,

Gillian

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