What diagnosis should be coded for hyperazotemia (elevated Blood Urea Nitrogen - BUN)?

From the Guidelines

If a patient has a high blood urea nitrogen (BUN) level, you should code for the underlying condition causing the elevated BUN rather than just coding for the lab abnormality itself. The most appropriate diagnosis code would depend on the specific cause, which could include dehydration (E86.0), acute kidney injury (N17.9), chronic kidney disease (N18.9), congestive heart failure (I50.9), gastrointestinal bleeding (K92.2), or other conditions affecting kidney function or protein metabolism [ 1 ]. A high BUN alone is considered a laboratory finding (R79.89) rather than a definitive diagnosis. To determine the correct code, review the patient's clinical presentation, other laboratory values (especially creatinine), medication history, and any documented clinical assessment [ 1 ]. The BUN-to-creatinine ratio can help distinguish between pre-renal causes (like dehydration) and intrinsic kidney disease. Some key causes of elevated BUN include:

• Cardiac conditions such as heart failure [ 1 ]
• Non-cardiac conditions such as renal dysfunction, liver dysfunction, and severe infections [ 1 ] For accurate coding, identify and document the underlying condition responsible for the elevated BUN, as this will guide appropriate treatment and follow-up care for the patient. It is also recommended to measure creatinine, BUN, and electrolytes every 1 – 2 days while in the hospital and before discharge from the hospital [ 1 ].

From the Research

Diagnosis for High BUN Levels

If a patient has a high Blood Urea Nitrogen (BUN) level, it may indicate Acute Kidney Injury (AKI). The following points should be considered for diagnosis:

• AKI is defined as an increase in serum creatinine or a decrease in urine output over hours to days 2
• The diagnosis of AKI can be made based on an increase in the serum creatinine level of 0.3 mg/dL or more within 48 hours, an increase of 1.5 times or more of the baseline level within 7 days, or a decrease in urine output to less than 0.5 mL/kg/hour for 6 hours 3
• Ultrasound assessment can be used to identify reversible causes of AKI or underlying chronic kidney disease, and can provide information on renal size, echogenicity, renal hilum, and vascularity 4, 5
• The history should focus on risk factors, including nephrotoxic drugs, and the physical examination should include determination of fluid volume status 3
• Urinalysis with microscopy can narrow the differential diagnosis, and management includes control of the underlying cause, achievement and maintenance of euvolemia, nutritional optimization, blood glucose control, and pharmacotherapy 3

Possible Causes and Management

Possible causes of high BUN levels include:

• Systemic illness or toxic exposure 3
• Nephrotoxic drugs 3
• Decrease in urine output 2, 3 Management of AKI includes:
• Control of the underlying cause 3
• Achievement and maintenance of euvolemia 3
• Nutritional optimization 3
• Blood glucose control 3
• Pharmacotherapy 3
• Referral to a nephrology subspecialist for patients with stage 2 or 3 AKI, or if the etiology of the AKI is unclear 3