Query Tip: Identifying Opportunities to Query for Acute Tubular Necrosis (ATN)

A primary function of queries is ensuring that coding is complete and accurately reflects the severity of the patient’s condition. Failing to code for diagnoses that are CCs or MCCs means the DRG assigned may not be the one that most appropriately reflects the resources required to care for the patient or their actual severity of illness or risk of mortality.

Since acute tubular necrosis is an MCC it is important for complete and accurate coding to identify if this diagnosis is suggested by clinical indicators when it is not specifically documented in the health record.

Recognizing an opportunity to query for acute tubular necrosis requires knowledge of its underlying pathophysiology and the clinical indicators suggesting its presence.

What is Acute Tubular Necrosis (ATN)?

Acute tubular necrosis (ATN) is a type of acute kidney injury that occurs when kidney tubules are damaged. Kidney tubules are tube shaped structures that filter salts, excess fluid and waste from the blood as urine is formed.

Image courtesy of Wikimedia

Causes:

Acute tubular necrosis has several causes, including reduced blood flow to the kidneys (ischemia), nephrotoxins and serious infections. The conditions that are most commonly associated with ATN are:

• Hypotension
• Use of nephrotoxic medications (IV contrast, acyclovir, cyclosporine, aminoglycosides, vancomycin, NSAIDs)
• Sepsis
• Hypovolemia
• Rhabdomyolysis
• Pancreatitis
• Multiple myeloma
• Tumor Lysis Syndrome
• Major surgery with blood loss causing hypotension
• Severe burns

Symptoms:

Some patients with ATN are asymptomatic, and the condition is only found through laboratory testing. If the condition is severe, symptoms may include:

• Decreased urine output (oliguria)
• Nausea and vomiting
• Weakness
• Fluid retention/swelling
• Mental changes (confusion, drowsiness, lethargy)

What are the Criteria for Diagnosing Acute Tubular Necrosis (ATN)?

Acute tubular necrosis is diagnosed through testing of the blood and urine. To establish a diagnosis of acute tubular necrosis, the patient should meet the criteria for Acute Kidney Injury (AKI) based on Kidney Disease Improving Global Outcomes (KDIGO) criteria:

AKI criteria (KDIGO)

• Increase in creatinine level to ≥ 1.5x baseline* (historical or measured), which is known or presumed to have occurred within the prior 7 days; or
• Increase (not decrease) in creatinine of ≥ 0.3 mg/dL comparing two separate levels, the second done within 48 hours or less of the first; or
• Urine output < 0.5 ml/kg/hr for 6 hours

AND

• Renal function, measured by creatinine levels, should take over 72 hours to return to near baseline after treatment.

If renal function returns within 72 hours acute kidney injury (AKI) is likely present rather than acute tubular necrosis (ATN).

Other abnormal lab values that indicate acute tubular necrosis include:

• Urine sodium concentration > 40 meq/L
• Urine specific gravity ≤ 1.010
• Fractional excretion of sodium (%) > 2
• Urine/plasma creatinine ratio < 20
• Urinary sediment contains muddy brown granular casts or renal tubular epithelial cells/casts

How is Acute Tubular Necrosis (ATN) Treated?

Treatment consists primarily of:

• Treating the underlying conditions (infection, shock/hypotension)
• IV fluids as needed to maintain normal blood flow to the kidneys
• Discontinuation of nephrotoxic medications

Dialysis may be required if patients do not respond to supportive care.

In healthy patients where the underlying condition is corrected and blood creatinine levels return to normal or near normal within 1 to 3 weeks, the prognosis for recovery is good. However, patients who survive acute tubular necrosis have an increased risk of developing chronic kidney disease.

Take Aways

• Appropriately querying for acute tubular necrosis ensures coding correctly reflects the patient’s clinical status and severity of illness
• Recognizing query opportunities requires knowledge of the pathophysiology, clinical indicators and treatments suggesting the presence of ATN
• ATN is caused by reduced blood flow to the kidneys (ischemia), nephrotoxins and serious infections
• Acute kidney injury is suggested in patients who meet the Kidney Disease Improving Global Outcomes (KDIGO) criteria
• Treatment is focused addressing the underlying cause and on restoring blood flow to the kidneys

References

• https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf
• https://www.merckmanuals.com/professional/genitourinary-disorders/tubulointerstitial-diseases/acute-tubular-necrosis-atn?query=acute%20tubular%20necrosis
• https://www.ncbi.nlm.nih.gov/books/NBK507815
• CDI Pocket Guide by Pinson & Tang: AKI and ATN