Nephrology Exam Domains 2026: Complete Guide to All 23 Content Areas

The AOBIM Nephrology Written Exam Blueprint Overview

The initial adult nephrology subspecialty Written Exam administered through the American Osteopathic Board of Internal Medicine (AOBIM), under the American Osteopathic Association (AOA), is built around a published outline of 23 distinct content areas. Every one of the 300 multiple-choice questions on the seven-hour exam is mapped to one of these areas, and the AOBIM assigns each a percentage range rather than a fixed weight - a detail candidates frequently misunderstand when they first review the blueprint.

If you're building a preparation plan, understanding exactly how these 23 domains are structured is arguably more important than any single fact you memorize. A candidate who spends equal time on all 23 areas will almost certainly underprepare for the domains that generate the most questions. This guide breaks down every domain, shows you the official percentage ranges, and explains how to sequence your review so the highest-yield material gets the attention it deserves. For a step-by-step preparation framework that goes beyond domain weighting, see our Nephrology Study Guide 2026.

Why the Percentage Ranges Matter for Your Prep

Each domain on the AOBIM outline is published as a range - for example, 2-6% or 8-12% - rather than a single fixed number. This means the exact number of questions from any given domain can shift slightly from one administration to the next, but the relative emphasis stays consistent. Domains with wider or higher ranges deserve proportionally more study hours because they represent a larger, more reliable share of your total possible points.

Practically, this means a candidate allocating study time should not treat all 23 domains as equal. A domain sitting at 1-3% (like Urolithiasis or Obstructive uropathy) will never generate more than a handful of questions, while Acid-base disorders/Renal tubular disorders at 8-12% could represent close to three dozen questions on a 300-item exam. Ignoring that gap is one of the most common - and most costly - planning mistakes.

The Three Highest-Yield Domains

Three domains stand out as the backbone of the exam. Together they can represent roughly a quarter or more of the entire test, depending on where each falls within its published range.

Because these three domains alone can account for a meaningful share of your total score, many candidates choose to schedule them earliest in their preparation timeline - a strategy detailed further in our Nephrology Cheat Sheet 2026, which condenses must-know facts from each high-weight domain onto a single reference page.

All 23 Content Areas, Explained

Below is the full outline, grouped by clinical theme so you can see how the domains relate to one another rather than treating each as an isolated checklist item.

Electrolyte and Metabolic Physiology

• Domain 1 - Fluid, acid-base, electrolyte physiology/renal function testing (2-6%): Foundational physiology, GFR estimation methods, and interpretation of basic renal function panels.
• Domain 2 - Mineral metabolism/disorders (PO4, Ca, Mg) (2-6%): Parathyroid-kidney axis, hypo/hyperphosphatemia, and magnesium wasting syndromes.
• Domain 3 - Hypo/Hypernatremia (2-6%): Volume status assessment, SIADH workup, and correction-rate safety limits.
• Domain 4 - Hypo/Hyperkalemia (1-5%): ECG correlation, transtubular potassium gradient concepts, and emergent management.

Acute and Toxicologic Kidney Disease

• Domain 6 - Acute kidney injury (7-11%): Covered above; the second-highest weighted domain.
• Domain 8 - Overdose/Toxic nephropathy/Intoxication (1-5%): Toxic alcohol ingestions, drug-induced tubular injury, and indications for extracorporeal removal.

Glomerular and Systemic Disease

• Domain 9 - Primary glomerular disease (5-9%): Membranous nephropathy, FSGS, minimal change disease, and IgA nephropathy presentations.
• Domain 10 - Secondary glomerular disease (4-8%): Lupus nephritis, infection-related GN, and paraprotein-associated kidney disease.
• Domain 11 - Diabetic nephropathy (2-6%): Staging, proteinuria management, and comorbid cardiovascular risk.
• Domain 17 - Vasculitis/Vascular disorders of kidney (1-5%): ANCA-associated vasculitis, thrombotic microangiopathies, and renal artery disease.

Chronic Disease Management and Renal Replacement

• Domain 12 - Hypertension (3-7%): Secondary hypertension workup and resistant hypertension strategies.
• Domain 13 - Chronic kidney disease (3-7%): Staging, complications, and timing of nephrology referral or dialysis planning.
• Domain 14 - Peritoneal dialysis (3-7%): Modality selection, peritonitis management, and prescription adequacy.
• Domain 15 - Hemodialysis (6-10%): Covered above; the third-highest weighted domain.
• Domain 16 - Renal transplantation (3-7%): Immunosuppression regimens, rejection patterns, and post-transplant complications.

Structural, Infectious, and Hereditary Disease

• Domain 18 - Tubulointerstitial disease (1-5%): Drug-induced interstitial nephritis and chronic tubulointerstitial injury patterns.
• Domain 19 - Urolithiasis (1-3%): Stone composition, metabolic workup, and prevention strategies.
• Domain 20 - Obstructive uropathy (1-3%): Etiologies of obstruction and post-obstructive diuresis management.
• Domain 21 - Urinary tract infections/Pyelonephritis (1-4%): Complicated versus uncomplicated infection management in kidney disease.
• Domain 22 - Cystic disease/UT Anomalies (2-6%): Autosomal dominant polycystic kidney disease and congenital anomalies.
• Domain 23 - Familial disorders of kidney (1-5%): Alport syndrome, familial FSGS, and other hereditary nephropathies.

Special Populations

• Domain 7 - Pregnancy and the kidney (1-3%): Preeclampsia, physiologic changes of pregnancy, and management of CKD in pregnant patients.

Domain Weight Reference Table

Use this table alongside our Nephrology Passing Score 2026 breakdown to understand how a scaled score of 500 or higher on the 200-800 scale relates to your performance across these ranges - the exam does not use a fixed raw percentage cutoff.

Building a Study Plan Around the Blueprint

Once you have the domain rankings in front of you, the actual scheduling logic is straightforward: front-load the highest-weighted domains, then work down the list, saving the narrowest domains (1-3%) for short review blocks near the end.

Spaced repetition across this seven-week arc works well specifically because it forces a second and third pass through the top three domains before test day, while still guaranteeing exposure to every one of the 23 areas at least once. If you need a fuller walkthrough of pacing, question review strategy, and how to handle the seven-hour testing day itself, our How Hard Is the Nephrology Exam? guide covers exam-day logistics in more depth.

How Registration and Fee Deadlines Affect Your Timeline

Domain mastery only matters if your application logistics are handled correctly. The standard 2026 examination fee is $800, and the published cycle adds a $240 late fee for applications submitted after June 16, with July 16 as the final application deadline. For the 2026 cycle, nephrology applications opened February 16. That gives candidates roughly five months from application opening to the final deadline - a window you should map directly onto your study calendar so your highest-intensity review weeks land before, not after, your submission date.

Eligibility itself is worth confirming early: candidates need primary AOA/AOBIM internal medicine certification, two years of ACGME-accredited or AOA-recognized nephrology fellowship training, active licensure, and program-director verification of clinical competence. Because board eligibility ends December 31 of the sixth year following training completion, candidates who delay their first attempt should track this window carefully alongside their domain study plan.

Who This Blueprint Actually Serves

The 23-domain outline isn't just an academic exercise - it reflects the actual clinical scope nephrologists are expected to manage day to day, from inpatient AKI consults to outpatient CKD and transplant follow-up to long-term dialysis center oversight. Employers hiring board-eligible or newly certified nephrologists generally expect fluency across this same range: acute inpatient consultation, chronic disease clinic management, and dialysis-unit medical direction. If you're weighing how this certification affects your career trajectory, our Nephrology Salary Guide 2026 and Is the Nephrology Certification Worth It? analysis both address how domain competency translates into practice readiness.

Whether you're early in fellowship or already deep into board prep, working systematically through practice questions organized by these same 23 domains - rather than random mixed sets - is one of the most efficient ways to close knowledge gaps before test day. You can start building that domain-by-domain familiarity with practice questions on our main practice test platform, which mirrors the blueprint's structure so you can track your readiness domain by domain rather than guessing where you stand overall.

Frequently Asked Questions