| Code | System | Description | Comment | Version |
| ASKU | http://hl7.org/fhir/v3/NullFlavor | asked but unknown | Information was sought but not found (e.g. patient was asked but didn't know | added v2.5 |
| N | http://hl7.org/fhir/v2/0136 | No | | added v2.5 |
| NA | http://hl7.org/fhir/v3/NullFlavor | not applicable | No proper value is applicable in this context (e.g. last menstrual period for a male) | added v2.5 |
| NASK | http://hl7.org/fhir/v3/NullFlavor | not asked | This information has not been sought (e.g. patient was not asked | added v2.5 |
| NAV | http://hl7.org/fhir/v3/NullFlavor | temporarily unavailable | Information is not available at this time but it is expected that it will be available later | added v2.5 |
| NI | http://hl7.org/fhir/v3/NullFlavor | No Information | No information whatsoever can be inferred from this exceptional value. This is the most general exceptional value. It is also the default exceptional value | added v2.5 |
| NP | http://hl7.org/fhir/v3/NullFlavor | not present | Obsolete as of v 2.7. | added v2.5 |
| UNK | http://hl7.org/fhir/v3/NullFlavor | unknown | A proper value is applicable, but not known | added v2.5 |
| Y | http://hl7.org/fhir/v2/0136 | Yes | | added v2.5 |