6.3 AKI, CKD Staging, UTI, and Urinary Stones

6.3 AKI, CKD Staging, UTI, and Urinary Stones

Quick Answer: Treat Kidney Disease: Improving Global Outcomes (KDIGO) creatinine and urine-output thresholds as clinical indicators, not as codes. Query unspecified renal insufficiency for acuity and chronic kidney disease (CKD) stage. Document acute kidney injury (AKI) on CKD when both are present. Distinguish catheter-associated urinary tract infection (CAUTI) from community-onset urinary tract infection (UTI) using POA relative to the inpatient order. Specify stones, obstruction, and infection as separate diagnostic questions.

This independent OpenExamPrep section is for inpatient CDI under IPPS. It cites KDIGO as a publicly used AKI framework. Neutral citation in a query is consistent with the 2026 ACDIS/AHIMA brief. Auto-coding AKI from a creatinine delta is not.

Kidney language is usually too vague

Progress notes recycle “renal insufficiency,” “elevated Cr,” “CKD,” “UTI,” and “kidney stone.” Those phrases do not tell the grouper whether the injury is acute, what CKD stage applies, whether a catheter is implicated, or whether a stone is obstructing or infected. Domain II expects you to know the physiology well enough to recognize indicators and to query for the missing diagnostic pieces.

AKI indicators versus a provider diagnosis

Acute kidney injury (also documented as acute kidney failure) is a sudden decline in glomerular filtration. KDIGO defines AKI using any of:

• Increase in serum creatinine by ≥0.3 mg/dL within 48 hours
• Increase in serum creatinine to ≥1.5 times baseline within the prior 7 days
• Urine volume <0.5 mL/kg/h for 6 hours

Those thresholds are indicators you may cite neutrally at the end of a query template. They are not an instruction to diagnose AKI, and they are not ICD-10-CM codes. A creatinine rise from 1.0 to 1.4 mg/dL in two days is a classic indicator; the diagnosis still belongs to the provider. KDIGO AKI stages 1–3 are additional clinical detail. If the provider documents a stage, capture it. Do not invent a stage from the lab strip.

Acute tubular necrosis (ATN), prerenal azotemia, and postrenal obstruction are etiologic refinements. If the attending writes “AKI” and nephrology writes “ATN from sepsis,” you have a more specific acute diagnosis. If the chart only shows a bump after diuretics, a query for prerenal injury versus ATN versus unspecified AKI may be warranted—without leading toward the option that yields a CC. Exact CC/MCC assignment depends on the current IPPS tables; this guide does not reprint them. Later-stage CKD and AKI frequently affect MS-DRG severity when they meet UHDDS criteria.

Chronic kidney disease is staged by estimated glomerular filtration rate (commonly stages 1–5 / G1–G5), with end-stage renal disease (ESRD) when the patient is on chronic dialysis. Unspecified CKD and “renal insufficiency” hide whether the patient is stage 3a or stage 5. Query “renal insufficiency” for:

• Acute, chronic, or acute-on-chronic
• CKD stage if chronic disease is present
• Dialysis dependence if applicable
• Etiology when it is already in the chart (diabetes, hypertension) and the relationship is not stated, following Official Guidelines on causal language

AKI on CKD is a real and reportable combination when both are documented. Do not let “baseline creatinine 2.4, now 3.8” remain labeled only as CKD. Do not let a transient bump overwrite a long-standing stage 4 diagnosis. Both stories can be true on one stay.

Common adult CKD banding used as indicators (not as codes you assign from eGFR alone): stage 1 GFR ≥90 with kidney damage; stage 2 60–89; stage 3a 45–59; stage 3b 30–44; stage 4 15–29; stage 5 <15. The provider still states the stage.

UTI, CAUTI, and POA

A urinary tract infection may be cystitis, pyelonephritis, or unspecified UTI. Pyelonephritis implies upper-tract involvement and a different picture (fever, flank pain, often a more aggressive treatment plan). Query unspecified “UTI” when imaging, fever, and bacteremia suggest pyelonephritis, or when the organism and site are named in culture but not in the provider assessment.

Catheter-associated UTI is both a clinical diagnosis and a quality construct. For claims, you need provider documentation that the UTI is associated with a urinary catheter. For CMS quality, CAUTI appears in two programs that must not be merged:

• HAC payment provision: urinary-catheter infection is one of the fourteen categories. When the condition is not POA, N or U generally prevents CC/MCC payment for that HAC. W is paid like Y.
• HAC Reduction Program: NHSN CAUTI is one of the infection measures in the Total HAC Score, alongside central line–associated bloodstream infection, selected surgical site infections, methicillin-resistant Staphylococcus aureus bacteremia, and Clostridioides difficile.

POA is still anchored to the inpatient order. A UTI diagnosed in the emergency department, even if a Foley is placed in the field after symptoms began, is generally POA = Y if the infection was present at the inpatient order. A CAUTI that develops on hospital day six after admission for hip fracture is typically POA = N and is HAC-relevant. Do not assign CAUTI merely because a catheter is present and the urinalysis is abnormal. Colonization and asymptomatic bacteriuria are not the same as a symptomatic UTI, and the provider must make that distinction.

Conditions arising in the emergency department, observation, or outpatient surgery before the inpatient order remain POA = Y. That rule saves many community UTIs from being mislabeled as hospital-acquired simply because the Foley went in during boarding.

Stones, obstruction, and infection

Nephrolithiasis, ureterolithiasis, and bladder stones are location-specific. The CDI questions are whether the stone is causing obstruction (hydronephrosis, forniceal rupture, post-renal AKI) and whether there is infection (pyelonephritis, pyonephrosis, infected hydronephrosis). A computed tomography report of a 7 mm ureteral stone with hydronephrosis is an indicator. “Kidney stone” in the history is not equivalent to acute obstruction.

Query separately when needed: presence of obstruction, presence of infection, and the relationship to AKI. Multiple-choice options must match the imaging. Do not offer “staghorn calculus with xanthogranulomatous pyelonephritis” when the scan shows a non-obstructing lower-pole stone and a bland urinalysis. Include Other, please specify. Yes/no may substantiate a radiologist’s already-documented hydronephrosis if a provider must confirm it; yes/no may not introduce obstruction from the radiology impression if no provider has named a urinary diagnosis.

Pharmacology indicators include angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, and nonsteroidal anti-inflammatory drugs in AKI, iodinated contrast exposure, and antibiotics for UTI. They support queries. They do not replace diagnoses.

Exam-style scenarios

Scenario: creatinine 1.0 to 1.5 in 48 hours. The hospitalist writes “renal insufficiency.” KDIGO creatinine change is an indicator, not a code. Query for AKI versus CKD versus AKI on CKD, and for CKD stage if a baseline exists. Do not drop “AKI stage 2” into the record from the calculator.

Scenario: Foley and a positive urinalysis. Day six after hip fracture, the nurse documents cloudy urine. Culture grows Escherichia coli. The attending writes “UTI.” A catheter is present. That is not yet CAUTI. Query for whether the UTI is catheter-associated, for site if pyelonephritis is in play, and for POA. If the infection began after the inpatient order and the provider links it to the catheter, POA N and HAC payment-provision logic may apply. If the same organism was already treated in the emergency department before the order, POA is Y.

Scenario: stone plus rising creatinine. CT shows an obstructing ureteral stone and hydronephrosis. Creatinine doubled. “Kidney stone” as the only diagnosis leaves obstruction and post-renal AKI on the table. Query obstruction and AKI as clinically relevant options; do not lead with an MCC label.

Scenario: mixing HAC programs. NHSN CAUTI surveillance definitions used by infection prevention are not identical to a coded CAUTI on the claim. The exam still expects you to keep HAC payment provision (fourteen categories, POA N/U versus Y/W) separate from HAC Reduction Program scoring (PSI-90 plus NHSN HAIs).

Study habits

For every kidney chart, ask four questions in order: acuity, chronic stage, infection source and POA, stone complications. Cite KDIGO the way you cite Academy/ASPEN: at the end, neutrally, never as a command. Confirm the inpatient-order timestamp before you call a UTI hospital-acquired.