Distinguish Active Kidney Stones From History of Stones
Question: Our nephrology office sees a 46-year-old established patient referred for recurrent kidney stones. The patient passed two stones in the past year and recently had a CT scan showing a nonobstructing 4 mm stone in the left kidney. The nephrologist reviews the outside imaging, orders a metabolic stone workup, and documents “recurrent calcium oxalate nephrolithiasis with current left renal calculus; 24-hour urine shows hypercalciuria and low urine citrate.” The plan includes increased fluid intake, reduced sodium intake, potassium citrate, and follow-up urine testing. Which ICD-10-CM code(s) are appropriate to report? South Dakota Subscriber Answer: Kidney stone coding depends on location, and you’re looking at three code options when you have anatomical specifics. “Kidney stone,” “renal calculus,” and “nephrolithiasis” generally support N20.0 (Calculus of kidney) when the stone is in the kidney. A stone that has moved into the ureter points to N20.1 (Calculus of ureter), and stones documented in both sites point to N20.2 (Calculus of kidney with calculus of ureter). If the documentation only says “urinary calculus” without a site, N20.9 (Urinary calculus, unspecified) may be the only supported choice. Remember, a query may be appropriate if the imaging report or provider note suggests a more specific location. In this case, imaging and provider documentation confirm a renal (kidney) location, so N20.0 is the most specific and appropriate code. The descriptor “nonobstructing” does not affect code selection. Coders should not report abnormal laboratory findings based solely on test results. In this case, you can report two additional diagnosis codes, as they are documented by the provider and addressed in the assessment and plan: R82.994 (Hypercalciuria) and R82.991 (Hypocitraturia). Sequence N20.0 first, as the current kidney stone is the primary condition being managed. Report the urine abnormality codes as additional diagnoses when they affect care, treatment decisions, or monitoring. Do not assign Z87.442 (Personal history of urinary calculi) for this encounter, as a current stone is present and being treated; history codes may be more appropriate for cases in which the patient has a prior history of stones without an active calculus. Although the provider documents “recurrent nephrolithiasis,” ICD-10-CM does not provide a separate code for recurrence. Code assignment is based on the current active condition instead of the recurrence descriptor. Rachel Dorrell, MA, MS, CPC-A, CPPM, Production Editor, AAPC
