2027 ICD-10-CM Diagnosis Code Z77.121Contact with and (suspected) exposure to harmful algae and algae toxins

ICD-10-CM Codes›Z00–Z99›Z77-Z99›suspected

ICD-10-CM Z77.121
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Z77.121 is a billable ICD-10-CM diagnosis code for contact with and (suspected) exposure to harmful algae and algae toxins. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 951. The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. Coders also document this condition as dermatosis caused by algae. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified status.

Code Identity

ICD-10-CM Code
Z77.121
Billable Status
Yes — Valid for Submission
Code Describes
Contact with and (suspected) exposure to harmful algae and algae toxins
Short Description
Contact w and exposure to harmful algae and algae toxins
Parent Code
Z77.12
Contact with and (suspected) exposure to hazards in the physical environment

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ77-Z99Persons with potential health hazards related to family and personal history and certain conditions influencing health status
CategorysuspectedOther contact with and exposures hazardous to health (Z77)
This CodeZ77.121Contact with and (suspected) exposure to harmful algae and algae toxins

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z77.121.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Present on Admission (POA)Billing

Z77.121 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Dermatosis caused by algae
  • Exposure to algae bloom
  • Harmful algal bloom

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Z77.121: its own notes plus those printed at Z77, block Z77-Z99, and Chapter 21. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Z77 Other contact with and (suspected) exposures hazardous to health applies to 31 codes
  • contact with and (suspected) exposures to potential hazards to health

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Contact with and (suspected) exposure to (harmful) algae bloom NOS
  • Contact with and (suspected) exposure to blue-green algae bloom
  • Contact with and (suspected) exposure to brown tide
  • Contact with and (suspected) exposure to cyanobacteria bloom
  • Contact with and (suspected) exposure to Florida red tide
  • Contact with and (suspected) exposure to pfiesteria piscicida
  • Contact with and (suspected) exposure to red tide

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Z77 Other contact with and (suspected) exposures hazardous to health applies to 31 codes
  • contact with and (suspected) exposure to communicable diseases (Z20.-)
  • exposure to (parental) (environmental) tobacco smoke in the perinatal period (P96.81)
  • newborn affected by noxious substances transmitted via placenta or breast milk (P04.-)
  • occupational exposure to risk factors (Z57.-)
  • retained foreign body (Z18.-)
  • retained foreign body fully removed (Z87.821)
  • toxic effects of substances chiefly nonmedicinal as to source (T51-T65)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Block Z77-Z99 Persons with potential health hazards related to family and personal history and certain conditions influencing health status applies to 567 codes
  • any follow-up examination (Z08-Z09)

Notes

General instructions on how these codes are used.

From Chapter 21 (Z00-Z99) Factors influencing health status and contact with health services applies to 1,425 codes
  • Z codes represent reasons for encounters. A corresponding procedure code must accompany a Z code if a procedure is performed. Categories Z00-Z99 are provided for occasions when circumstances other than a disease, injury or external cause classifiable to categories A00-Y89 are recorded as 'diagnoses' or 'problems'. This can arise in two main ways:
  • (a) When a person who may or may not be sick encounters the health services for some specific purpose, such as to receive limited care or service for a current condition, to donate an organ or tissue, to receive prophylactic vaccination (immunization), or to discuss a problem which is in itself not a disease or injury.
  • (b) When some circumstance or problem is present which influences the person's health status but is not in itself a current illness or injury.

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Z77.121, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming Z77.121: they are not reported together with it, unless the two conditions are unrelated.

  • Block T51-T65 Toxic effects of substances chiefly nonmedicinal as to source
    contact with and (suspected) exposure to toxic substances (Z77.-) names Z77.-, which includes this code
  • Z03 Encounter for medical observation for suspected diseases and conditions ruled out
    contact with and (suspected) exposures hazardous to health (Z77.-) names Z77.-, which includes this code
  • Z13.88 Encounter for screening for disorder due to exposure to contaminants
    those exposed to contaminants without suspected disorders (Z57.-, Z77.-) names Z77.-, which includes this code
  • Z92.3 Personal history of irradiation
    exposure to radiation in the physical environment (Z77.12) names Z77.12, which includes this code

Excludes2 4

These codes carry an Excludes2 note naming Z77.121: its condition is not part of those codes, and both may be reported when the patient has both.

  • P04 Newborn affected by noxious substances transmitted via placenta or breast milk
    newborn in contact with and (suspected) exposures hazardous to health not transmitted via placenta or breast milk (Z77.-) names Z77.-, which includes this code
  • Z59.1 Inadequate housing
    problems related to the natural and physical environment (Z77.1-) names Z77.1-, which includes this code
  • Z91 Personal risk factors, not elsewhere classified
    contact with and (suspected) exposures hazardous to health (Z77.-) names Z77.-, which includes this code
  • Z91 Personal risk factors, not elsewhere classified
    exposure to pollution and other problems related to physical environment (Z77.1-) names Z77.1-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR FAC025
Other specified status
Default principal diagnosis: inpatient No · outpatient Yes

Patient EducationClinical

Water Pollution

We all need clean water. People need it to grow crops and to operate factories, and for drinking and recreation. Fish and wildlife depend on it to survive.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert Z77.121 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
V87.32 Contact/exp algae bloom
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Z77.121Overview

Is Z77.121 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report contact with and (suspected) exposure to harmful algae and algae toxins on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does Z77.121 group to?

On inpatient claims, contact with and (suspected) exposure to harmful algae and algae toxins maps to MS-DRG 951 (other Factors Influencing Health Status), which carries a relative weight of 0.5574. Higher weights mean higher Medicare reimbursement.

Can Z77.121 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because contact with and (suspected) exposure to harmful algae and algae toxins describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Is Z77.121 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for contact with and (suspected) exposure to harmful algae and algae toxins on inpatient claims. The code appears in the Persons with potential health hazards related to family and personal history and certain conditions influencing health status (Z77-Z99) range of the CMS exempt list.

What is the ICD-9 equivalent of Z77.121?

Under the General Equivalence Mappings, contact with and (suspected) exposure to harmful algae and algae toxins converts to ICD-9-CM V87.32 (contact/exp algae bloom). The mapping is approximate, so confirm the match fits the documentation.