Renal Pathology, Pathology, USMLE Step 1 - Full Vignette with Extended Explanations

Описание: A 26-year-old pregnant woman presents with new-onset ankle swelling and a background of family kidney disease. She has mild bilateral ankle edema but normal vital signs and most laboratory findings, with only trace proteinuria noted. With a history of extensive unrelated medical evaluations and concern about her kidney health during pregnancy, what is the optimal strategy for assessing renal function in pregnant patients, and which laboratory or clinical features should guide decision-making in this scenario?

VIDEO INFO
Category: Renal Pathology, Pathology, USMLE Step 1
Difficulty: Moderate - Intermediate level - Requires solid foundational knowledge
Question Type: Recent Changes
Case Type: Pregnant Patient

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QUESTION
A 26-year-old woman at 22 weeks gestation presents to the obstetric clinic with new ankle swelling and concern about possible kidney disease because her mother required dialysis in her 40s. She has an inguinal hernia repaired in adolescence. She is unemployed, stopped alcohol 10 years ago, and takes only prenatal vitamins. Allergies include quinolones (joint pain), penicillin (anaphylaxis), and mold exposure (coughing)....

OPTIONS
A. During pregnancy, assess kidney function with serial serum creatinine and, when needed, timed creatinine clearance; avoid eGFR equations, including race-free CKD-EPI.
B. During pregnancy, estimate kidney function with the 2021 race-free CKD-EPI creatinine equation and confirm with cystatin C when results are borderline, following recent U.S. adoption.
C. During pregnancy, use Cockcroft-Gault eGFR with actual body weight because hyperfiltration would otherwise be missed.
D. During pregnancy, use MDRD eGFR for staging CKD and drug dosing because it has the widest clinical experience.

CORRECT ANSWER
A. During pregnancy, assess kidney function with serial serum creatinine and, when needed, timed creatinine clearance; avoid eGFR equations, including race-free CKD-EPI.

EXPLANATION
During pregnancy, estimated GFR equations perform poorly because of physiologic changes in creatinine generation and filtration; guidelines recommend serial serum creatinine and, when needed, a timed creatinine clearance rather than eGFR. KDIGO 2024 emphasizes that common eGFR equations-including the 2021 race-free CKD-EPI-are not validated for pregnancy. The 2019 pregnancy and renal disease guideline similarly recommends measured creatinine clearance if an estimate is required. The NKF-ASN 2021 race-free equation is intended for non-pregnant populations.

This patient at 22 weeks (second trimester) has normal creatinine and mild albuminuria (ACR 65 mg/g). Monitoring with serum creatinine and urine protein assessment is appropriate; avoid eGFR-based staging or drug dosing.

In summary, the correct answer is to use serial serum creatinine and timed creatinine clearance when needed, avoiding eGFR equations during pregnancy.

Primary teaching point: eGFR equations (CKD-EPI, MDRD, Cockcroft-Gault) are unreliable in pregnancy; rely on serum creatinine trends and measured clearance when necessary.

Secondary teaching point: Race-free CKD-EPI 2021 is a non-pregnant standard; it does not override pregnancy-specific limitations.


Further reading:

Links to sources are provided for optional further reading only. The questions and explanations are independently authored and do not reproduce or adapt any specific third-party text or content.

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