The Daily Differential — Saturday, May 16, 2026

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Contrast-Induced Nephropathy

Contrast-associated AKI is often overestimated but still matters in high-risk patients. Fear of kidney injury should not delay life-saving imaging, but ED...

At the Bedside

Terminology: Modern literature often uses contrast-associated AKI because kidney injury after contrast may be due to illness, hypotension, sepsis, or nephrotoxins rather than contrast itself.
Highest-risk patients:
eGFR <30 mL/min/1.73 m².
AKI already present.
Kidney transplant, severe dehydration, shock, sepsis, large contrast load, concurrent nephrotoxins.
Diabetes alone is not a major independent risk unless CKD is present.
ED decision principle:
If imaging is urgent/life-saving — stroke CTA, trauma CT, aortic dissection, PE with instability — do the study.
If nonurgent and eGFR severely reduced, consider alternative imaging or pre/post hydration.
Workup:
BMP/creatinine when risk factors or institutional screening criteria present.
Review baseline creatinine if available.
Assess volume status: dehydration, vomiting, diuretics, sepsis, hypotension.
Identify nephrotoxins: NSAIDs, aminoglycosides, amphotericin, high-dose diuretics, ACEi/ARB in selected unstable patients.
Prevention:
Use low- or iso-osmolar iodinated contrast.
Minimize contrast volume when feasible.
Isotonic IV fluids are the main preventive strategy in high-risk patients who can tolerate fluids.
Avoid dehydration and hypotension.
Hold nonessential nephrotoxins when feasible.
What does not reliably help:
N-acetylcysteine is not routinely recommended.
Sodium bicarbonate is not clearly superior to normal saline; institutional practices vary.
Prophylactic dialysis after contrast is not recommended solely to remove contrast.
Metformin issue:
Main concern is lactic acidosis if AKI develops.
Many protocols hold metformin in patients with eGFR <30, AKI, or intra-arterial contrast; restart after renal function stable. Follow institutional policy.
Disposition:
Most patients receiving contrast do not need admission solely for kidney monitoring.
High-risk discharged patients should receive hydration advice, avoid NSAIDs, and obtain repeat creatinine in 48–72 hours if clinically appropriate.

A Classic Presentation

A 76-year-old with CKD stage 4 presents with tearing chest pain radiating to the back and unequal arm BPs. Creatinine is 2.8 mg/dL, eGFR 24. The ED team proceeds with CTA for suspected aortic dissection because diagnostic delay is life-threatening, gives isotonic IV fluids as tolerated, avoids NSAIDs, and consults vascular surgery when CTA confirms type B dissection.

Study Directive

Memorize the high-risk threshold: eGFR <30 or AKI.
Write a one-sentence contrast counseling script for CKD patients.
Review your hospital’s metformin/contrast policy.
Practice 3 scenarios where contrast should proceed despite CKD: dissection, stroke CTA, unstable trauma.

Key Medications

Normal saline prophylaxis: common regimen 1 mL/kg/hr IV for 3–12 hr before and 6–12 hr after contrast when feasible.
- In ED urgent imaging, give isotonic fluids before/after as practical.
- Reduce rate in CHF/ESRD/volume overload risk.
Alternative rapid hydration: 0.9% saline 3 mL/kg/hr for 1 hr before, then 1 mL/kg/hr after — protocol dependent.
Sodium bicarbonate: variable protocols; not clearly superior to saline. If used, verify institutional regimen.
N-acetylcysteine: not routinely recommended.
Pediatrics: prevention is also hydration and minimizing contrast; dosing/fluids should be weight-based and protocol-driven.

High-Yield Pearls

eGFR <30 or active AKI is the key risk zone; diabetes without CKD is not enough to prohibit contrast.
Normal saline is the only consistently supported preventive intervention.
Never trade a theoretical kidney risk for a missed dissection, stroke LVO, major trauma injury, or unstable PE.

Board Question

A patient with eGFR 22 presents with sudden severe chest pain radiating to the back, pulse deficit, and hypotension. The physician is concerned about aortic dissection. What is the best next step?

AAvoid CTA because contrast is absolutely contraindicated
BGive N-acetylcysteine and discharge for outpatient MRI
CProceed with emergent CTA while providing renal-protective supportive care
DDelay imaging for 24 hours of IV hydration

Reveal answer

Correct: C

Suspected aortic dissection is life-threatening, and indicated contrast imaging should not be delayed solely due to CKD. Hydration and avoidance of nephrotoxins are reasonable, but diagnosis and definitive management take priority.

Recent Literature

Review or guideline [Prevention of contrast-induced nephropathy]
Rev Med Liege, 2024

Full text · open access
Recent clinical Contrast Induced Nephropathy in Trauma: A Real Phenomenon?
Am Surg, 2026

3 of 4

Endometritis

Postpartum endometritis is a common cause of postpartum fever and can progress to sepsis, pelvic abscess, septic pelvic thrombophlebitis, or necrotizing...

At the Bedside

Definition: Infection/inflammation of the endometrial lining, usually polymicrobial ascending infection.
Risk factors:
Cesarean delivery, prolonged rupture of membranes, prolonged labor, multiple vaginal exams, internal fetal monitoring.
Retained products, postpartum hemorrhage, manual placental extraction.
STIs and bacterial vaginosis.
Typical presentation:
Fever, uterine/fundal tenderness, lower abdominal/pelvic pain.
Foul-smelling lochia, malaise, tachycardia.
Usually within 2–10 days postpartum but can occur later.
Exam:
Full vitals/sepsis screen.
Abdominal exam for fundal tenderness/peritonitis.
Pelvic exam if tolerated: lochia, cervical motion tenderness, bleeding, retained tissue concern.
Inspect C-section incision, breasts, urine source, lungs — postpartum fever has a broad differential.
Workup:
Pregnancy/postpartum status and delivery details.
CBC, CMP, lactate if septic, blood cultures if ill-appearing or high fever.
UA/urine culture; consider GC/CT testing if STI risk.
Pelvic ultrasound if heavy bleeding, concern for retained products, abscess, or poor response to antibiotics.
CT abdomen/pelvis if peritonitis, abscess, necrotizing infection, or unclear diagnosis.
Initial management:
Sepsis care if unstable: IV access, fluids, broad-spectrum antibiotics early, source control.
Most postpartum endometritis requires inpatient IV antibiotics.
Consult OB/GYN early, especially post-cesarean, septic, retained products, abscess, or persistent bleeding.
Definitive therapy:
First-line classic regimen: IV clindamycin + gentamicin until afebrile and clinically improved, often 24–48 hr.
Add ampicillin if enterococcus concern or no improvement.
If retained products or septic abortion suspected, source control with uterine evacuation may be required.
Disposition:
Admit: postpartum fever with uterine tenderness, sepsis, post-cesarean infection, inability to tolerate PO, concern for retained products/abscess.
Outpatient management is uncommon for true postpartum endometritis; mild late presentations require OB-directed decision-making.

A Classic Presentation

A 25-year-old presents 5 days after C-section with fever, chills, lower abdominal pain, and foul lochia. She is tachycardic, has fundal tenderness, and her incision appears clean. UA is equivocal, WBC is elevated, and lactate is normal. She is started on IV clindamycin plus gentamicin, OB is consulted, and she is admitted for postpartum endometritis.

Study Directive

Memorize the classic regimen: clinda 900 IV q8 + gent 5 mg/kg IV q24.
Build a postpartum fever differential: endometritis, UTI/pyelo, mastitis, wound infection, pneumonia, DVT/PE, drug fever.
Review ultrasound findings of retained products and when OB source control is needed.
Practice presenting this consult to OB in 30 seconds: delivery date/mode, fever, uterine tenderness, lochia, vitals, antibiotics given.

Key Medications

Clindamycin: 900 mg IV q8 hr.
Gentamicin: 5 mg/kg IV q24 hr commonly used; dosing depends on renal function and institutional protocol. Verify levels/protocol.
Ampicillin: 2 g IV q6 hr if enterococcus concern or inadequate response.
Alternative broad regimens:
- Ampicillin-sulbactam: 3 g IV q6 hr.
- Piperacillin-tazobactam: 4.5 g IV q6 hr for severe/septic cases or broader intra-abdominal concern.
Septic abortion coverage: broad IV antibiotics plus urgent OB/GYN source control; regimens vary — verify protocol.
Analgesia/antipyretic: acetaminophen 650–1,000 mg PO/IV q6 hr PRN.
Pediatrics/adolescents: same principles, weight-based dosing and OB/GYN involvement.

High-Yield Pearls

Postpartum fever + fundal tenderness = endometritis until proven otherwise.
C-section is the strongest common risk factor for postpartum endometritis.
Persistent fever despite appropriate antibiotics should raise concern for retained products, abscess, resistant organism, or septic pelvic thrombophlebitis.

Board Question

A postpartum patient presents 4 days after cesarean delivery with fever, uterine tenderness, and foul-smelling lochia. What is the most appropriate initial antibiotic regimen?

AFluconazole PO once
BClindamycin plus gentamicin IV
CAzithromycin PO once only
DCephalexin PO outpatient

Reveal answer

Correct: B

Postpartum endometritis is polymicrobial and classically treated with IV clindamycin plus gentamicin. Cesarean delivery is a major risk factor, and most cases require admission.

Recent Literature

Review or guideline Endometritis - Diagnosis,Treatment and its impact on fertility - A Scoping Review
JBRA Assist Reprod, 2022 · cited 101×

Full text · open access
Recent clinical The Equine Reproductive Microbiota: Composition, Dynamics, Dysbiosis, and Implications for Fertility in Mares and Stallions
Animals (Basel), 2026

Full text · open access

4 of 4

Gynecologic Infections

Gynecologic infections range from benign vaginitis to PID, tubo-ovarian abscess, ectopic mimic, sepsis, and infertility risk. ED management must combine...

At the Bedside

First step in reproductive-age pelvic complaints: pregnancy test.
Ectopic pregnancy can mimic PID or pelvic infection.
Key syndromes:
Cervicitis: mucopurulent discharge, friable cervix, postcoital bleeding; commonly GC/CT.
PID: pelvic/lower abdominal pain plus cervical motion tenderness, uterine tenderness, or adnexal tenderness.
Tubo-ovarian abscess: PID plus fever, adnexal mass, severe pain, vomiting, leukocytosis.
BV: thin gray discharge, fishy odor, clue cells.
Trichomoniasis: frothy discharge, vulvar irritation, strawberry cervix sometimes.
Candida: thick white discharge, pruritus, vulvar erythema; pH usually normal.
Bartholin abscess: painful unilateral posterior introitus mass.
History:
LMP, pregnancy risk, contraception/IUD, sexual partners, STI history, discharge/odor, dyspareunia, dysuria, fever, vomiting.
Ask about sexual assault if context suggests.
Exam:
Abdominal exam for peritonitis.
Pelvic exam: discharge, cervical friability, CMT, uterine/adnexal tenderness, adnexal mass.
External exam for HSV lesions, chancres, vulvar abscess.
Testing:
Urine/serum hCG.
NAAT for gonorrhea/chlamydia; NAAT for trich if available.
Wet mount/KOH if available: clue cells, trichomonads, yeast.
UA/culture if urinary symptoms.
HIV/syphilis testing as indicated; offer STI screening.
Pelvic ultrasound if adnexal tenderness/mass, severe pain, pregnancy, torsion/TOA concern, or uncertain diagnosis.
PID treatment threshold:
Treat empirically if pelvic/lower abdominal pain with CMT, uterine tenderness, or adnexal tenderness and no better alternative diagnosis.
Do not wait for GC/CT results.
Admit for PID/TOA if:
Pregnancy, severe illness/sepsis, tubo-ovarian abscess, inability to tolerate PO, failed outpatient therapy, diagnostic uncertainty/surgical emergency not excluded.
Partner/public health:
Treat/notify partners for GC/CT/trich.
Abstain from sex until treatment complete, symptoms resolved, and partners treated.
Retest GC/CT/trich in ~3 months.

A Classic Presentation

A 19-year-old presents with 2 days of pelvic pain, mucopurulent discharge, and dyspareunia. Pregnancy test is negative. Pelvic exam shows cervical motion tenderness and bilateral adnexal tenderness without mass. She is afebrile and tolerating PO. GC/CT NAATs are sent, and she is treated empirically for PID with ceftriaxone IM, doxycycline, and metronidazole, with partner counseling and 48–72 hour follow-up.

Study Directive

Memorize outpatient PID therapy exactly: ceftriaxone + doxy x14 + metronidazole x14.
Create a one-page vaginitis comparison: BV vs trich vs Candida by pH, discharge, microscopy, treatment.
Practice pelvic pain disposition decisions: outpatient PID vs admit for TOA/sepsis/pregnancy/failed PO.
Review partner treatment and abstinence counseling for GC/CT/trich.

Mechanism Pearl of the Day: Pregnancy and the postpartum state are prothrombotic, immunomodulated, and anatomically altered — the same physiologic changes that increase PE risk also increase susceptibility to ascending polymicrobial genital tract infections and complicate diagnostic decision-making.

Key Medications

Outpatient PID:
- Ceftriaxone 500 mg IM once; use 1 g IM once if ≥150 kg.
- Doxycycline 100 mg PO BID x14 days.
- Metronidazole 500 mg PO BID x14 days.
Inpatient PID/TOA common regimen:
- Ceftriaxone 1 g IV q24 hr plus doxycycline 100 mg PO/IV q12 hr plus metronidazole 500 mg PO/IV q12 hr.
- Continue until improved, then complete 14 total days.
Gonorrhea cervicitis/urethritis:
- Ceftriaxone 500 mg IM once; 1 g if ≥150 kg.
- Add doxycycline 100 mg PO BID x7 days if chlamydia not excluded.
Chlamydia:
- Doxycycline 100 mg PO BID x7 days.
- Pregnancy alternative: Azithromycin 1 g PO once.
Bacterial vaginosis:
- Metronidazole 500 mg PO BID x7 days.
Trichomoniasis:
- Women: Metronidazole 500 mg PO BID x7 days.
- Men: metronidazole 2 g PO once.
Vulvovaginal candidiasis:
- Fluconazole 150 mg PO once.
- Pregnancy: avoid oral fluconazole; use topical azole x7 days.
Genital HSV first episode:
- Acyclovir 400 mg PO TID x7–10 days or valacyclovir 1 g PO BID x7–10 days.
Bartholin abscess:
- Incision/drainage with Word catheter if appropriate.
- Antibiotics only if cellulitis, pregnancy, immunocompromise, recurrent infection, systemic symptoms, or STI concern.
Pediatrics/adolescents: use weight-based dosing where applicable; maintain confidentiality laws, mandatory reporting rules, and pregnancy/STI testing.

High-Yield Pearls

PID is a clinical diagnosis; negative GC/CT testing does not exclude upper genital tract infection.
Pregnancy test is mandatory before labeling pelvic pain as infection.
TOA requires admission, IV antibiotics, and possible drainage if large, ruptured, or not improving.

Board Question

A nonpregnant 22-year-old has pelvic pain, cervical motion tenderness, and mucopurulent cervical discharge. She is afebrile, stable, and tolerating oral intake. Pregnancy test is negative. What is the best ED treatment?

AWait for gonorrhea/chlamydia results before treating
BCeftriaxone IM once plus doxycycline and metronidazole for 14 days
CFluconazole PO once only
DAmoxicillin-clavulanate only

Reveal answer

Correct: B

PID is treated empirically when clinical criteria are met because delayed treatment increases infertility and chronic pelvic pain risk. Standard outpatient therapy includes gonorrhea, chlamydia, anaerobic, and BV-associated organism coverage.

Recent Literature

Review or guideline Human Papillomavirus and Associated Cancers: A Review
Viruses, 2024 · cited 99×

Full text · open access
Recent clinical Gut microbiome and pregnancy complications: emerging evidence and mechanistic insights
Gut Microbes, 2026

Full text · open access

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