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AFHSB Surveillance Case Definitions
Case Definition and Incidence Rules
For surveillance purposes, a case of exertional hyponatremia is defined as:
One hospitalization or outpatient medical encounter with a case defining diagnosis of
exertional hyponatremia (seeICD9 and ICD10 code lists below) in the primary diagnostic
position.
One hospitalization or outpatient medical encounter with a case defining diagnosis of
exertional hyponatremia in any diagnostic position PLUS at least one associated condition
(see ICD9 and ICD10 code lists below) in diagnostic positions 1- 3.
Incidence rules:
For individuals who meet the case definition:
The incidence date is considered the date of the first hospitalization or outpatient medical
encounter that includes a defining diagnosis of exertional hyponatremia.
An individual is considered an incident case only once per calendar year.
Exclusions:
Cases of exertional hyponatremia that include any of the complicating diagnoses (see ICD
and ICD10 code lists below) in any diagnostic position.
HYPONATREMIA; EXERTIONAL
Background
This case definition was developed by the Armed Forces Health Surveillance Branch (AFHSB) for the
purpose of epidemiological surveillance of exertional hyponatremia. The case definition is intended to
cases potentially preventable through well-known measures to safeguard healthy service members
training or carrying out their duties under conditions associated with high ambient temperature and
strenuous exertion.
Clinical Description
Hyponatremia is defined as a low concentration of sodium in the blood (i.e., serum sodium
concentration <135mEq/L); it can have serious and sometimes fatal clinical effects. In otherwise
healthy, physically active adults (e.g., long distance runners, military recruits), hyponatremia is often
associated with excessive water consumption during prolonged physical exertion (exertional
hyponatremia), particularly during heat stress.^1
1 Armed Forces Health Surveillance Center. Update: Exertional Hyponatremia, Active Component,
U.S. Armed Forces, 1999-2010. Medical Surveillance Monthly Report (MSMR). March 2011 Vol
AFHSB Surveillance Case Definitions
Codes
The following ICD9 and ICD10 codes are included in the case definition:
Condition ICD-10-CM Codes ICD-9-CM Codes
Hyponatremia E87.1 (hypo-osmolality and/or hyponatremia) 276.1 (hypo-osmolality and/or hyponatremia)
Associated Conditions
Condition ICD-10-CM Codes ICD-9-CM Codes
Fluid overload, somnolence, stupor and coma
E87.7 (fluid overload) 1. 276.6 9 (fluid overload)
- E87.70 (fluid overload, unspecified)
- E87.79 (other fluid overload) R40 (somnolence, stupor and coma) 780.0 (alteration of consciousness) R40.0 (somnolence) - 780.09 (other alteration of consciousness) R40.1 (stupor) R40.2 (coma) (^) - 780.01 (coma)
- R40.20 (unspecified coma)
- R40.21^ (coma scale, eyes open)
- R40.211^ (coma scale, eyes open, never )
- R40.212^ (coma scale, eyes open, to pain )
- R40.213^ (coma scale, eyes open, to sound )
- R40.214^ (coma scale, eyes open, spontaneous )
- R40.22^ (coma scale, best verbal response)
- R40.221^ (coma scale, best verbal response, none )
- R40.222^ (coma scale, best verbal response, incomprehensible words )
- R40.223^ (coma scale, best verbal response, inappropriate words )
- R40.224^ (coma scale, best verbal response, confused conversation )
- R40.225^ (coma scale, best verbal response, oriented )
AFHSB Surveillance Case Definitions
- T67.2XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.3 (heat exhaustion, anhydrotic…) 992.3 (heat exhaustion, anhydrotic)
- T67.3XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.4 (heat exhaustion due to salt depletion…) 992.4 (heat exhaustion due to salt depletion)
- T67.4XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.5 (heat exhaustion, unspecified…) 992.5 (heat exhaustion, unspecified)
- T67.5XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.6 (heat fatigue, transient…) 992.6 (heat fatigue, transient)
- T67.6XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.7 (heat edema…) 992.7 (heat edema)
- T67.7XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.8 (other effects of heat and light…) 992.8 (other specified heat effects)
- T67.8XX [A,D,S] (initial encounter, subsequent encounter, sequela) T67.9 (effect of heat and light, unspecified…) 992.9 (unspecified effects of heat)
- T67.9XX [A,D,S] (initial encounter, subsequent encounter, sequela) Rhabdomyolysis M62.82 (rhabdomyolysis) 728.88 (rhabdomyolysis)
Exclusions: Complicating Diagnoses
ICD-10-CM Codes (^ = all digits) ICD-9-CM Codes (* = all digits)
A00.^ - A09.^ (intestinal infectious diseases) 001.- 009. (intestinal infectious diseases)
C00.^ - D49.^ (neoplasms) 3. 140.* - 239.* (neoplasms)
E00.^ - E36.^ (disorders of thyroid gland, diabetes mellitus, other disorders of glucose regulation and pancreatic internal secretion, and disorders of other endocrine glands. 240.* - 259.* (diseases of thyroid and other endocrine glands) F01.^ - F99.^ (mental, behavioral and neurodevelopmental disorders) 290.* - 319.* (mental, behavioral and neurodevelopmental disorders) G00.^ - G09.^ (inflammatory diseases of the central nervous system) 320.* - 326.* (inflammatory diseases of the central nervous system)
AFHSB Surveillance Case Definitions G10.^ - G13.^ (systemic atrophies primarily affecting the central nervous system) 330.* - 337.* (hereditary and degenerative diseases of the central nervous system) G20.^ - G32.^ (extrapyramidal and movement disorders, other degenerative diseases of the nervous system) J12.^ - J18.^ (pneumonia) 480.* - 486.* (pneumonia) K20.^ - K31.^ (diseases of the esophagus, stomach, duodenum) 530.* - 539.* (diseases of esophagus, stomach and duodenum) K35.^ - K38.^ (diseases of the appendix) 540.- 543. (appendicitis) K50.^ - K52.^ (noninfectious enteritis and colitis) 555.* - 558.* (noninfectious enteritis and colitis) K55.^ - K64.^ (other diseases of intestines) 560.* - 569.* (other diseases of intestines and peritoneum) K65.^ - K95.^ (diseases of the peritoneum and retroperitoneum, diseases of the liver, disorders of gallbladder, biliary tract and pancreas, and other diseases of the digestive system) 570.* - 579.* (other diseases of digestive system) N00.^ - N23.^ (glomerular disease, renal tubule- interstitial diseases, acute kidney failure and chronic kidney disease, urolithiasis) 580.* - 589.* (nephritis, nephrotic syndrome, and nephrosis) N25.^ - N39.^ (other disorders of kidney and ureter, other diseases of the urinary system) 590.* - 599.* (other diseases of urinary system) N70.^ - N77.^ (inflammatory diseases of female pelvic organs) 614.* - 616.* (inflammatory disease of female pelvic organs) N80.^ - N99.^ (noninflammatory disorders of female genital tract, intraoperative and postprocedural complications and disorders of genitourinary system, not elsewhere classified) 617.* – 629.* (other disorders of female genital tract) O00.^ - O9A.^ (pregnancy, childbirth, and the puerperium) 630.* - 679.* (complications of pregnancy, childbirth, and the puerperium) P00.^ - P96.^ (certain conditions originating in the perinatal period) 760.* - 779.* certain conditions originating in the perinatal period) S^2^ (fractures) 800.* - 829.* (fractures) S03. 0 ^ - S03. 2 ^ (dislocations head) S13. 0 ^ - S13. 2 ^ (dislocations neck) S23. 0 ^ - S23. 2 ^ (dislocations thorax) S33. 0 ^ - S33. 4 ^ (dislocations lumbar spine and pelvis) S43. 0 ^ - S43. 3 ^ (dislocations shoulder girdle) S53. 0 ^ - S53. 3 ^ (dislocations elbow and forearm) S63. 0 ^ - S63. 4 ^ (dislocations wrist, hand, fingers) S73. 0 ^ - S73.4^ (dislocations hip and thigh) S83. 0 ^ - S83. 3 ^ (dislocation joints and ligaments of knee) 830.* - 839.* (dislocations)
AFHSB Surveillance Case Definitions T51.^ - T65.^ (toxic effects of substances chiefly nonmedicinal as t source) 980.* - 989.* (toxic effects of substances chiefly nonmedicinal as to source) T80.^ - T88.^ (complications of surgical and medical care, not elsewhere classified) 996.* - 999.* (complications of surgical and medical care, not elsewhere classified) Z08.^ - Z09.^ (encounter for follow-up examination after completed treatment for malignant neoplasm, encounter for follow-up examination after completed treatment for conditions other than malignant neoplasm) V67.0 (examination following surgery) Z40.^ - Z51.^ (encounters for other specific health care) V50-V56 (health services for specific procedures and aftercare) Z98.^ (other postprocedural states) V45 (other postprocedural states)
Development and Revisions
In March of 2017 the case definition was updated to include ICD10 codes
This case definition was originally developed in 1997 by the Army Medical Surveillance Activity
(AMSA) for an article on hyponatremia. In the summer of 1997, Army training centers reported
eight hospitalizations of soldiers for hyponatremia secondary to excessive water consumption
during military training in hot weather – one case was fatal, and several others required intensive
medical care. 2
Case Definition and Incidence Rule Rationale
Cases of hyponatremia that are less susceptible to prevention through organized procedures and
practices may be associated with alcohol/illicit drug abuse, mental disorders, endocrine disorders,
kidney diseases, infectious diseases, cancers, major traumatic injuries, or complications of medical
care (see complete, detailed list under Exclusions: Complicating Diagnoses [above]) and are
excluded from this definition. The exclusionary conditions have been expanded for this case
definition and are more numerous than the conditions previously used for this definition.
Code Set Determination and Rationale
The diagnostic code specific for rhabdomyolysis, (i.e., 728.88) was added to the ICD-9-CM in 2004.
Therefore, it may not be possible to detect cases of hyponatremia associated with rhabdomylysis prior
to that time if the hyponatremia diagnosis was not in the first diagnostic position and there were no
other associated conditions documented in the record.
The case definition includes codes with 7th^ digits “A” (initial encounter), “D” (subsequent
encounter) and “S” (sequela). Analyses using these codes might increase the sensitivity of case-
finding in health care records. Given that the incidence rules permit an individual to be considered
an incident case only once per calendar year , it would be unlikely for combinations of diagnoses
with A, D, and S 7th^ digits in a patient’s record to be counted as repeat events.
2 Army Medical Surveillance Activity. Hyponatremia associated with heat stress and excessive water
consumption: Fort Benning, GA; Fort Leonard Wood, MO; Fort Jackson, SC June -August 1997.
Medical Surveillance Monthly Report (MSMR). 1997 Sep; 3(6): 2-8.
AFHSB Surveillance Case Definitions
Reports
AFHSB reports on hyponatremia in the following reports:
Annual MSMR update. The most recent update was in March 2017.^3
Review
Mar 2017 Case definition reviewed and updated by the AFHSB Surveillance Methods and
Standards (SMS) working group.
Jul 2011 Case definition reviewed and adopted by the AFHSC Surveillance Methods and
Standards (SMS) working group.
Mar 2011 Case definition developed and reviewed by the AFHSC MSMR staff.
Comments
None
3 Armed Forces Health Surveillance Branch. Update: Exertional hyponatremia, active component,
U.S. Armed Forces, 2001 - 2016. Medical Surveillance Monthly Report (MSMR). 2017 March; Vol 24
