Topic:Metabolic Acidosis
What to look for in the labs, how the E87.2- codes break down, and when a query may be clinically supported.
Definition
Metabolic acidosis is a primary acid-base disorder characterized by a reduction in serum bicarbonate (HCO₃⁻), resulting from increased acid production or accumulation, bicarbonate loss, or impaired renal acid excretion.
Diagnosis requires evaluation of the patient's overall clinical presentation, laboratory findings, and acid-base status. A low bicarbonate level alone does not establish metabolic acidosis, as it may also occur in other acid-base disturbances. When clinically supported, provider documentation should identify the diagnosis, acuity (acute or chronic), and underlying etiology.
Metabolic acidosis is generally classified as high anion gap metabolic acidosis (HAGMA) or normal anion gap metabolic acidosis (NAGMA). The serum anion gap helps distinguish these categories and is commonly calculated as:
Anion Gap = Sodium (Na⁺) − [Chloride (Cl⁻) + Bicarbonate (HCO₃⁻)]
Baseline
The measured cation (sodium) is balanced by chloride, bicarbonate, and the unmeasured anions that make up the gap.
High anion gap (HAGMA)
Bicarbonate falls and the gap widens to fill the difference.
Normal anion gap (NAGMA)
Bicarbonate falls, chloride rises to take its place, and the gap stays within range.
Some laboratories include potassium in the calculation. Interpretation should consider the laboratory's established reference range and serum albumin level, as hypoalbuminemia may mask an elevated anion gap.
Clinical Indicators and Diagnostic Considerations
Common clinical indicators include:
Elevated anion gap
An anion gap above the laboratory's established reference range, interpreted in the context of serum albumin.
Normal anion gap metabolic acidosis
Reduced bicarbonate with a normal anion gap, often accompanied by a relative increase in chloride.
- Review lactate when clinically indicated
- Correlate laboratory findings with the patient's clinical presentation and underlying disease process
Clinical note: Laboratory thresholds and reference ranges may vary by institution.
*Refer to your organization's established protocols and laboratory reference ranges when interpreting results and evaluating metabolic acidosis
Coding Considerations
For inpatient reporting, ensure that metabolic acidosis meets the applicable criteria for reporting an additional diagnosis under Section III of the ICD-10-CM Official Guidelines for Coding and Reporting.
ICD-10-CM codes for metabolic acidosis were updated and expanded on 10/1/2022 (for FY 2023). There are now four codes in subcategory E87.2-
Metabolic acidosis may be:
Acute
E87.21Commonly associated with sepsis, dehydration, AKI, DKA, toxins, diarrhea, or lactic acidosis.
Chronic
E87.22Commonly associated with chronic kidney disease (CKD).
ICD-10-CM Coding Clinic Acute and Chronic Metabolic Acidosis, 4th quarter, 2022 p. 14
Accurate documentation of metabolic acidosis, including its acuity and underlying etiology when clinically supported, helps ensure the medical record accurately reflects the patient's clinical complexity and supports appropriate coding, quality reporting, and severity assessment.
CDI Practice Considerations
Review:
*Laboratory abnormalities should be evaluated alongside the patient's clinical presentation, underlying conditions, treatment, and provider documentation. When clinically supported, a query may be appropriate to clarify an undocumented diagnosis or its specificity.
Look for common associated diagnoses:
Treatment often includes:
- IV fluid resuscitation
- Correction of the underlying cause
- Electrolyte replacement
- Sodium bicarbonate (select patients)
- Insulin for DKA
- Antibiotics when infection is present
Query Opportunity
Consider a query when clinically significant acid-base abnormalities are supported by the patient's overall clinical presentation, evaluation, monitoring, or treatment, but the associated diagnosis or its specificity remains unclear in the provider documentation.
Potential indicators warranting further review may include:
Persistent reduction in serum bicarbonate with additional clinical evidence of an acid-base disturbance.
An elevated anion gap, interpreted in the context of laboratory reference ranges and serum albumin.
Acute kidney injury or chronic kidney disease accompanied by persistent bicarbonate abnormalities.
Sepsis or other acute conditions associated with clinically significant metabolic disturbances.
Gastrointestinal bicarbonate loss, diabetic ketoacidosis, or other conditions associated with metabolic acidosis.
Treatment directed at an underlying acid-base disturbance when the corresponding diagnosis is unclear.
CDI Best Practice Reminder
When reviewing for metabolic acidosis, evaluate the complete clinical picture, including laboratory trends, acid-base status, underlying conditions, treatment, and provider documentation. Determine whether clarification is clinically supported and ensure any query is compliant, nonleading, and consistent with organizational policy.