Case 07: The Grandmother's Urine Cup

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Session S3 · 2026-10-28 · in-session · 37 min Anchor: Urinalysis as the skeleton key — contaminated specimen, UTI vs asymptomatic bacteriuria, pyelonephritis · Integrates: Geriatric confusion work-up (medications, dehydration, thiazide hyponatremia), CKD drug dosing, outpatient creatinine-bump triage, renal imaging choice One-line hook: The most common antibiotic prescription you will be asked to write as a new PA is for a confused older woman with a "positive" urine. This case is about what that cup can and cannot tell you, and where else to look.

Learning Objectives

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1. Judge whether a urine specimen is interpretable from the microscopy (squamous epithelial cells, mucus threads, mixed bacterial forms) and decide whether further urine testing is clinically indicated before choosing a collection method.
2. State what leukocyte esterase and nitrite each detect, what each misses, and why a positive dipstick in an older adult does not confirm infection.
3. Apply the two indications for screening and treating asymptomatic bacteriuria, and manage "delirium plus bacteriuria" without an antibiotic.
4. Build a delirium work-up for an older adult with CKD: renally cleared drugs dosed by creatinine clearance, anticholinergics, volume status by orthostatic vitals, thiazide hyponatremia, and the creatinine bump.
5. For true pyelonephritis in a patient with CKD, choose admission vs outpatient care, an antibiotic by kidney function (and name the one never to use), and the trigger and modality for imaging.

Warm-Up (individual commit before the case)

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Part 1 — Presentation

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Mrs. Marjorie Lund, 84, arrives by wheelchair van from her assisted-living facility at 10:40 on a Tuesday. The transfer sheet says, in the nurse's handwriting: "UTI — please treat. Positive UA attached. Fell last night."

She has lived at the facility for two years. At baseline she walks with a cane, knows the staff by name, manages her own pills from a weekly box, and has mild memory trouble (oriented to person and place, forgets appointments). She has type 2 diabetes for twenty years, hypertension, painful burning in both feet from diabetic neuropathy, and chronic kidney disease — her last clinic labs three months ago showed creatinine 1.4 mg/dL, eGFR 37 mL/min/1.73 m² (CKD-EPI 2021), urine albumin-to-creatinine ratio 210 mg/g, hemoglobin A1c 7.2: CKD G3b A2, diabetic kidney disease.

Two things changed in the last month. Four weeks ago her primary care clinic added hydrochlorothiazide 25 mg for blood pressure readings in the 160s. One week ago, after she called about her feet, her gabapentin was tripled from 300 mg to 900 mg three times daily. For the last five nights the facility has given her a 25-mg diphenhydramine tablet at bedtime from the PRN list because she "couldn't settle."

Three days ago she stopped finishing meals. Two days ago an aide found her "not herself" — sleepy in the afternoon, calling the aide by her daughter's name. The facility nurse collected a urine specimen into a collection bag applied over an incontinence pad (she could not follow the clean-catch instructions) and sent it for urinalysis and culture. Last night she got up to use the toilet, fell, and was found on the floor by her bed. No head strike was witnessed; she has a bruise over the left hip. This morning the urinalysis result came back and generated the transfer.

She is a widow. Her daughter lives two hours away and holds her health-care power of attorney. She does not drink alcohol. She has never had a urinary catheter.

Vitals (ED, 10:55): T 36.9 °C · Pulse 78 seated → 98 standing · BP 138/74 seated → 110/62 standing · Resp 16 · SpO₂ 96 percent on room air · Weight 52.0 kg (facility weight 4 weeks ago: 54.5 kg) · Height 158 cm. Read the orthostatic change against the table in the quick-start guide, Part 6.

Exam. Drowsy but rousable; oriented to person only; cannot name the month; attention wanders mid-sentence (she cannot recite the months backward past October). Mucous membranes dry. Skin over the forearm tents slowly — remember that turgor is unreliable in the elderly, which is why we took orthostatics. Neck veins flat at 30°. Lungs clear. Heart regular, no murmur. Abdomen soft, no suprapubic fullness, no costovertebral-angle tenderness. No peripheral edema. Occasional brief myoclonic jerks of both hands at rest. No focal weakness, no asterixis (the flapping hand tremor of uremia or liver failure). Left hip bruised, full passive range of motion without pain. No dysuria, frequency or incontinence beyond her baseline nocturia, per the facility.

Medications on arrival

The urinalysis the facility sent (bag specimen, collected 2 days ago)

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Part 2 — Data

Answers for this section: Q7 · Q8

The straight-catheter specimen is obtained at 11:30. The rest of the ED work-up returns over the next two hours.

Blood (ED, 11:10) with her baseline from clinic 3 months ago

A note on the osmolality: measured 278 looks normal only because BUN adds 42/2.8 = 15 mOsm/kg. Urea crosses cell membranes and does not pull water, so it is excluded from effective osmolality: 2 × 127 + 158/18 = 263. This is true hypotonic hyponatremia.

A note on the glucose: the glucose-corrected sodium is 127 + 1.6 × (158 − 100)/100 = 128 mEq/L, so glucose is not the explanation for the sodium.

Urine studies (catheter specimen)

Urinalysis — straight-catheter specimen (ED, 11:30)

Other results - Bladder scan after voiding: post-void residual 60 mL (no retention). - Non-contrast CT head (for the fall with new confusion): no hemorrhage, no mass; age-appropriate atrophy. - Left hip and pelvis radiographs: no fracture. - 12-lead ECG: sinus rhythm 80/min, normal intervals, no T-wave or QRS change. - The facility's culture (from the bag specimen sent 2 days ago) posts at 13:15: "Mixed urogenital flora, 3 organisms, 10,000–50,000 CFU/mL each — suggests contamination; recollect if clinically indicated."

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Part 3 — Course and Decisions

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Mrs. Lund is admitted to the medical floor at 14:30. Orders: hydrochlorothiazide, gabapentin and diphenhydramine stopped; metformin and lisinopril held; isotonic saline 500 mL over one hour, then 75 mL/h; sodium every 6 hours with a hard stop if it rises more than 8 mEq/L in 24 hours; fall precautions; no urinary catheter; no antibiotic. Her daughter arrives at 16:00 and confirms that "Mom was sharp two weeks ago."

Before we follow her, a counterfactual: the same woman, a different cup.

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Back to the real Mrs. Lund. Sodium 127 at 11:10 → 130 at 17:00 → 132 at 23:00 → 134 at 11:00 the next morning: a rise of 7 mEq/L in 24 hours, under the ceiling. The saline is stopped on hospital day 2 once she is drinking. Creatinine 1.9 → 1.7 (day 2) → 1.5 (day 3) → 1.4 (day 4, back to baseline). The myoclonus is gone by the second morning; by the third she knows the month and asks whether anyone has fed her cat. At her clearance gabapentin takes days, not hours, to wash out — the drug was still leaving her on day 3.

Resolution and Teaching Points

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Mrs. Lund returns to assisted living on hospital day 4 with amlodipine 2.5 mg daily in place of hydrochlorothiazide, lisinopril and metformin resumed at their prior doses, atorvastatin and PRN acetaminophen unchanged, gabapentin restarted at 100 mg at bedtime, and diphenhydramine removed from her PRN list. The gabapentin plan is to titrate no higher than the label's 200–700 mg/day band for her clearance (a lower patient-specific dose may be preferable because of her prior toxicity) and to reassess whether it helps her feet at all; the diphenhydramine is replaced with non-drug sleep measures, because anticholinergics in older adults mean delirium, falls and urinary retention — which is why they sit on the Beers list of drugs to avoid in older adults . Her discharge letter to the facility says three things in plain language: no bag specimens for urinalysis — a clean catch with an aide's help, or a straight catheter when the question is real; confusion, by itself, is not a urinary symptom; and any new drowsiness, fall or poor intake gets a same-day sodium and creatinine, not an antibiotic. Her primary care clinic rechecks a BMP in one week (sodium 138, creatinine 1.4) and at the visit her daughter asks the question every family asks: "If it wasn't a UTI, why does everyone always say it is?" The honest answer is that the cup is easy to send and the medication list is hard to read.

Clinical Pearl — Read the specimen before the result Many squamous epithelial cells (more than 5–10 per low-power field, lpf — Mohr's cutoff was more than 8/lpf ), mucus threads and bacteria of several shapes on one slide mean the urine ran across the perineum. That urinalysis cannot tell you about the bladder. Recollect: clean catch with help, or a straight catheter when cognition or mobility make a clean catch impossible. Never force an interpretation onto a bad sample.

Clinical Pearl — The dipstick is a rule-out test Both infection pads negative (leukocyte esterase and nitrite) lowers the odds of infection in every population. A positive leukocyte esterase in an older woman is close to uninformative on its own. Nitrite needs about 4 hours of bladder dwell time and a nitrate-reducing organism; frequency, diuretics and Enterococcus all blank the pad.

Clinical Pearl — "Delirium plus bacteriuria" is not a diagnosis Established ASB treatment indications include pregnancy and endourologic procedures with mucosal trauma. IDSA recommends against treating bacteriuria for isolated delirium or falls in older adults without local urinary or systemic infection signs. Other special populations have separate recommendations or evidence gaps. Obtain a urine culture for a clinical indication, not to explain every episode of confusion.

Clinical Pearl — Labels dose by creatinine clearance, not eGFR Follow the renal-function measure specified by the particular drug label; CrCl and indexed eGFR are not interchangeable. Gabapentin uses a creatinine-clearance table: >15–29 mL/min, 200–700 mg once daily; at 15, 100–300 mg/day, with proportionate reduction below 15. This is a reference range, not a mandate to reach its upper end. Frailty, indication and adverse effects guide the actual dose.

Clinical Pearl — Thiazide hyponatremia can have different volume patterns and can overcorrect Stop the thiazide and assess volume and neurologic symptoms. This patient is volume-depleted, so cautiously replace the deficit while monitoring sodium and urine output. Other thiazide-associated cases appear euvolemic. Restoration of water excretion can cause rapid correction; use an explicit limit and escalation plan. Avoid rechallenge after this severe episode.

Pitfall — Treating the number instead of the patient An antibiotic for 8 WBC/hpf in a bag specimen. Fluid restriction for a sodium of 127 before anyone checked orthostatic vitals. A nephrology call for a creatinine of 1.9 before the bladder scan and the medication review. Each one skips the five-minute step that would have changed the plan.

Pitfall — Nitrofurantoin for the wrong patient Nitrofurantoin is not appropriate for pyelonephritis because it does not provide adequate renal tissue treatment. Renal thresholds differ between the US label and prescribing guidance; the commonly used CrCl <30 avoidance rule is not the original label threshold. Her CrCl near 25 and suspected upper-tract illness both argue against it. Select an alternative from the clinical syndrome, cultures and local susceptibility data.

Concept Links

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Assigned reading: the explanations in this case and the question-linked course evidence guide. The objective map distinguishes tested decisions from concepts taught in explanations.

Concepts: aki-06, aki-27, ckd-18, glom-01, glom-02, lytes-01, lytes-06, structural-04, structural-05, structural-14, structural-18, structural-25.