- What the AOBIM Nephrology Written Exam Actually Tests
- Registration, Fees, and Deadlines You Cannot Miss
- The 23 Domains: Where to Put Your Hours
- A Domain-Weighted Study Timeline
- Exam Format, Pacing, and Scoring
- Eligibility Checkpoints Before You Apply
- After You Pass: OCC and the Ten-Year Cycle
- Frequently Asked Questions
- Acid-base/renal tubular disorders carries the highest weight at 8-12% - anchor your review here first.
- Standard fee is $800; a $240 late fee applies after June 16, with a July 16 final deadline.
- Passing requires a scaled score of 500+ on a 200-800 scale, not a fixed raw percentage.
- The exam is 300 questions across seven hours - pacing practice matters as much as content review.
What the AOBIM Nephrology Written Exam Actually Tests
The Certification in Nephrology credential, awarded through the American Osteopathic Board of Internal Medicine (AOBIM) under the American Osteopathic Association (AOA), validates that a physician has completed nephrology fellowship training and can independently manage the full breadth of adult kidney disease. This guide focuses specifically on the initial adult nephrology subspecialty Written Exam - not a general internal medicine exam, and not a different society's nephrology credential. If you've landed here searching for an AOBIM nephrology board review or an AOBIM nephrology blueprint, this is the exam you're preparing for.
Understanding what separates this exam from adjacent credentials matters. If you're weighing what Nephrology Certification actually verifies versus other internal medicine subspecialty pathways, or you want the AOBIM vs ABIM nephrology distinction spelled out, keep that separation in mind throughout your prep - the blueprint, eligibility rules, and scoring model described here apply only to the AOBIM pathway.
Registration, Fees, and Deadlines You Cannot Miss
Application mechanics are where well-prepared candidates lose ground unnecessarily. For the 2026 cycle, nephrology applications opened February 16 and closed July 16, with the initial-subspecialty examination window set for August 12-14. The standard examination fee is $800. Miss the June 16 cutoff and a $240 late fee is added on top of the standard fee - so building your calendar around these dates is as important as building your study calendar.
- Application opens: February 16
- Late fee triggers: After June 16 (+$240)
- Final application deadline: July 16
- Exam window: August 12-14
For a full breakdown of every fee, including rescore costs, see Nephrology Certification Cost 2026: Complete Pricing Breakdown. If you want the deadlines laid out on their own timeline with reminders, Nephrology Exam Dates 2026: Testing Windows, Deadlines & Scheduling covers that in depth.
Key Takeaway
Submit your application well before June 16. Waiting until the July 16 deadline costs you an extra $240 for no benefit - that money is better spent on a question bank or review course.
The 23 Domains: Where to Put Your Hours
The official Written Exam outline lists 23 topic areas, each with a published percentage range rather than a fixed weight. Three domains stand out as the highest-yield: Acid-base disorders/Renal tubular disorders (8-12%), Acute kidney injury (7-11%), and Hemodialysis (6-10%). Together these three areas can represent close to a third of the entire exam, which means your study plan should be built around them rather than treating all 23 domains as equal.
Domain 5: Acid-base disorders/Renal tubular disorders (8-12%)
The single highest-weighted domain. Candidates must be fluent in mixed acid-base disorders, anion gap and non-anion gap metabolic acidosis, respiratory compensation formulas, and the classic renal tubular acidosis subtypes.
- Be able to distinguish Type 1, Type 2, and Type 4 RTA by urine pH, serum potassium, and underlying mechanism
- Practice multi-step acid-base problems that combine two or more primary disorders
Domain 6: Acute kidney injury (7-11%)
Expect heavy emphasis on prerenal, intrinsic, and postrenal differentiation, contrast-associated AKI, and the transition from AKI to CKD.
- Know urine microscopy findings that distinguish ATN from prerenal azotemia
- Understand indications and timing for renal replacement therapy initiation in AKI
Domain 15: Hemodialysis (6-10%)
The third-highest weighted domain covers vascular access, dialysis prescription, complications, and adequacy assessment.
- Master Kt/V calculations and adequacy targets
- Know complications of hemodialysis access, including thrombosis and steal syndrome
Beyond the top three, don't neglect the mid-weighted clinical domains - Primary glomerular disease (5-9%), Secondary glomerular disease (4-8%), Chronic kidney disease (3-7%), Peritoneal dialysis (3-7%), Renal transplantation (3-7%), and Hypertension (3-7%) - since collectively these account for a substantial share of scored items. A full breakdown of all 23 areas, including the lower-weighted domains like Pregnancy and the kidney (1-3%), Urolithiasis (1-3%), and Obstructive uropathy (1-3%), is available in Nephrology Exam Domains 2026: Complete Guide to All 23 Content Areas.
| Domain | Weight Range |
|---|---|
| Acid-base disorders/Renal tubular disorders | 8-12% |
| Acute kidney injury | 7-11% |
| Hemodialysis | 6-10% |
| Primary glomerular disease | 5-9% |
| Secondary glomerular disease | 4-8% |
| Chronic kidney disease | 3-7% |
| Peritoneal dialysis | 3-7% |
| Renal transplantation | 3-7% |
| Hypertension | 3-7% |
| Fluid/acid-base/electrolyte physiology | 2-6% |
A Domain-Weighted Study Timeline
A generic weekly study template is only useful if it's mapped onto the actual blueprint. Below is one way to sequence a 12-week plan so the heaviest-weighted domains get the most repetition, with lighter domains grouped into combined review weeks.
Acid-base disorders/Renal tubular disorders + Fluid/electrolyte physiology
- Work through mixed acid-base problem sets daily
- Drill RTA subtypes until pattern recognition is automatic
Acute kidney injury + Hemodialysis
- Build a comparison chart of AKI etiologies with distinguishing labs
- Practice Kt/V and dialysis adequacy calculations under time pressure
Primary and secondary glomerular disease
- Correlate biopsy patterns with clinical presentations
- Review complement and serologic workups for glomerulonephritis
CKD, hypertension, diabetic nephropathy, transplantation
- Focus on CKD staging and progression management
- Review immunosuppression regimens and post-transplant complications
Electrolyte disorders, mineral metabolism, peritoneal dialysis
- Drill hypo/hypernatremia and hypo/hyperkalemia algorithms
- Review PTH-vitamin D-phosphate physiology
Lower-weighted domains + full timed practice
- Cover urolithiasis, obstructive uropathy, UTIs, cystic disease, familial disorders, vasculitis, tubulointerstitial disease, pregnancy, and toxic nephropathy in combined review sessions
- Take full-length timed practice blocks to build seven-hour stamina
Use spaced repetition for recall-heavy items like RTA classification and drug-induced nephrotoxicity lists, but reserve most of your remaining time for applied practice questions rather than passive review - the exam's 300-question format rewards pattern recognition speed over memorization alone.
Exam Format, Pacing, and Scoring
The Written Exam contains 300 multiple-choice questions administered over seven hours. That works out to roughly 1.4 minutes per question if you want even pacing across the full test, though complex vignette-style questions in domains like acid-base disorders and glomerular disease will take longer than straightforward recall items in domains like urolithiasis or obstructive uropathy.
Passing requires a scaled score of at least 500 on a 200-800 scale - this is not a fixed raw percentage, so don't fixate on "getting X out of 300 correct" as your benchmark. For a detailed explanation of how the scaled scoring model works and what it means for your preparation targets, see Nephrology Passing Score 2026: Exactly What You Need to Pass. If you're trying to gauge overall difficulty before committing to a study plan, How Hard Is the Nephrology Exam? Complete Difficulty Guide 2026 and Nephrology Pass Rate 2026: What the Data Shows both provide useful context.
Eligibility Checkpoints Before You Apply
Before you pay the $800 fee, confirm you meet every eligibility requirement - reapplying after a rejected application wastes both time and money. To sit for the initial Written Exam, candidates need:
- Primary AOA/AOBIM internal medicine certification already in hand
- Two years of ACGME-accredited or AOA-recognized nephrology fellowship training
- Active, unrestricted medical licensure
- Program-director verification confirming clinical competence and completed training
- Compliance with AOA ethical requirements
General board policy also accepts qualifying COCA-accredited osteopathic or LCME-accredited medical graduates who complete the applicable accredited training, though subspecialty-specific requirements still apply on top of that baseline. One detail candidates frequently overlook: board eligibility ends December 31 of the sixth year following training completion, so fellows who delay applying for several years after finishing training should track that clock carefully. A complete walkthrough of every requirement, including documentation specifics, is available in Nephrology Requirements 2026: Eligibility, Prerequisites & How to Qualify.
Key Takeaway
If you finished fellowship several years ago and haven't yet certified, check your December 31 eligibility cutoff before assuming you still qualify to apply.
After You Pass: OCC and the Ten-Year Cycle
Certification carries a ten-year term, but it's not a "pass once and forget it" credential - it's subject to successful Osteopathic Continuous Certification (OCC). For the 2025-2027 cycle, time-limited diplomates must complete 60 CME credits over three years, including at least 15 Category 1 and/or Category 1-A credits, maintain active licensure, complete one quality-improvement activity attestation per three-year cycle, and pass the required subspecialty OCC cognitive examination.
The nephrology OCC cognitive exam is offered annually in August through remote proctoring, and diplomates may sit for it as early as two years before their certificate's expiration date. Passing early has a practical advantage: it preserves your original renewal anniversary rather than resetting your cycle. Planning your OCC exam attempt two years out, rather than waiting until the final year, gives you a buffer if something unexpected interferes with your first attempt.
Thinking about the career-long picture - how certification maintenance fits into practice patterns, hiring, and compensation - is worth doing before you even sit for the initial exam. See Nephrology Salary Guide 2026: Complete Earnings Analysis and Is the Nephrology Certification Worth It? Complete ROI Analysis 2026 for that broader context, and Nephrology Jobs for how certification factors into hospital and group hiring decisions.
Building Your Question Bank Practice Around the Blueprint
Generic AOBIM nephrology practice questions are only useful if you're tracking your accuracy by domain, not just overall percentage correct. Since acid-base/renal tubular disorders, acute kidney injury, and hemodialysis together make up such a large share of scored items, a candidate scoring 90% on low-weight domains like pregnancy and the kidney or familial disorders but only 60% on acid-base disorders is in worse shape than the raw average suggests. Tag every practice question by domain as you go, and revisit Nephrology Cheat Sheet 2026: One-Page Review of Must-Know Facts in your final two weeks for rapid-fire recall of high-yield facts across all 23 areas.
Our practice test platform is built directly around this 23-domain blueprint, so you can drill the highest-weighted areas first and see your domain-level accuracy rather than just a final score. Pairing full-length timed sets from the practice exam engine with your fellowship reading is generally more efficient than passive textbook review alone, especially in the final month before your August exam window.
Frequently Asked Questions
You need a scaled score of at least 500 on a 200-800 scale. This is not a fixed raw percentage of the 300 questions - it's a scaled result, so focus your prep on mastering high-weight domains rather than estimating a raw score target.
The standard examination fee is $800. If you apply after June 16, a $240 late fee is added, making the total $1,040. The final application deadline is July 16.
Acid-base disorders/Renal tubular disorders (8-12%) is the highest-weighted domain, followed by Acute kidney injury (7-11%) and Hemodialysis (6-10%). These three domains combined represent a substantial portion of the exam and should anchor your early study weeks.
The Written Exam contains 300 multiple-choice questions administered over seven hours. Practicing full-length timed blocks in advance helps build the stamina needed for this format.
Certification is valid for ten years but requires Osteopathic Continuous Certification (OCC). For the 2025-2027 cycle, that means 60 CME credits over three years (including 15 Category 1/1-A credits), active licensure, a quality-improvement attestation, and passing the OCC cognitive exam, which is offered annually in August and can be taken up to two years before expiration.