Why Nurse Practitioners and PAs Get Sued: Diagnostic Misses, Prescribing Errors, and Why Co-Defendant Cases Cost More

By John Mahoney · June 2026 · 9 min read

Advanced practice providers — nurse practitioners and physician assistants — are named in a small share of malpractice cases, and the closed-claims data consistently shows they carry no greater per-provider risk than physicians. But that headline hides the part that matters to litigators: APP cases behave differently when a supervising physician is in the caption. The co-defendant dynamic, the supervision question, and the diagnostic-process failures that dominate APP claims make these cases their own category — one growing in practical importance as APPs deliver more front-line care.

This guide is for plaintiff and defense med-mal attorneys screening APP claims. It covers the frequency-and-severity reality (with an important data caveat), the diagnostic-and-prescribing allegation profile, the failures that drive claims, the supervision and co-defendant dynamics that raise payouts, and what separates a strong APP case from a weak one.

Disclaimer: This article is for informational purposes only and does not constitute legal advice or a medical opinion. A key methodological caveat applies throughout: the landmark Jena et al. (NEJM 2011) physician study excluded NPs and PAs entirely, so there is no Jena frequency figure for APPs, and the figures below (anchored to NPDB and Candello/CNA-NSO data) should not be compared one-to-one with the physician percentages used for other specialties.

The Frequency-and-Severity Reality (and the Data Caveat)

By relative claim frequency, APPs run low. NPDB data (2005–2014) showed malpractice payment reports of roughly 1.4–2.4 per 1,000 PAs — substantially lower than physicians; one analysis found one payment per roughly 32.5 PAs versus one per 2.7 physicians, with the physician composite payment rate around twelve times that of PAs. Candello/CRICO data (more than 135,000 cases, 2012–2021) named APPs as a defendant in only about 2% of all cases and as a contributing factor in about 8% — with no significant difference in risk versus physicians and no rise in APP claim share despite rapid workforce growth.

On severity, APP payouts run medium-low — generally below physicians, but with high-severity outliers. CNA/NSO data (NP claims closed 2017–2021) reported an average total incurred around $332,000, with diagnosis-related claims higher (around $386,000; referral-management failures around $443,000). NPDB median payments tell the same story: PA median around $80,000 versus physician median around $151,000. Neonatal and pediatric NP claims carry the highest severity because of lifelong-care costs.

The figure that should change how you value an APP case is this: when APPs are co-defendants with physicians, those cases are more likely to result in payment and have higher average payouts. In the emergency department, one analysis found APPs and trainees involved in about 21% of cases but roughly 33% of gross indemnity. The APP is rarely the whole case — but an APP in a co-defendant posture often raises the value of the whole case.

The Dominant Allegation Types

APP claims are predominantly cognitive, not procedural — which puts them on the diagnostic-error side of the master axis, alongside primary care and internal medicine:

• Diagnosis-related (missed, delayed, or wrong diagnosis) — the single largest category: about 37.1% of NP claims (CNA/NSO) and a striking 52.8% of PA claims in NPDB analysis.
• Medication management / prescribing errors — around 29% of NP claims, and a leading driver of state licensing-board complaints.
• Treatment and care management — around 22% of NP claims.
• Scope-of-practice / standard-of-care violations — prominent in licensing-board actions against NPs specifically.
• Surgical/procedural and monitoring failures — more relevant for PAs in surgical and emergency-medicine settings.

Because the dominant theory is diagnostic, the merit logic mirrors a cognitive-specialty case: was an indicated test ordered, was an abnormal result acted on, was the differential adequate, and was a "cannot-miss" condition in the window?

The Cannot-Miss Failures That Drive APP Claims

APP diagnostic claims share a remarkably consistent process fingerprint. The dominant failure point is not exotic — it is the test that was never ordered and the result that was never acted on. Screen for these on both sides:

• Failure to order appropriate diagnostic or lab tests to establish a diagnosis — the single dominant failure mode, present in about 59.3% of diagnosis-related claims. This is the heart of the APP diagnostic case.
• Missed cancers — failure to diagnose reproductive (breast, ovarian) and lung cancer, and unaddressed abnormal screening (chest x-ray, PSA, mammogram, abnormal labs). The classic "Big Three" cancer miss, reached through an unordered or unactioned test.
• Failure to obtain a complete history and physical / patient assessment — about 19.8% of diagnosis claims.
• Failure to refer or obtain timely specialist consultation — about 15.1% of diagnosis claims, and the costliest sub-category in the severity data.
• Missed infections and acute conditions in urgent-care and ED settings — pediatric febrile illness, sepsis, cardiac events — plus neonatal and pediatric injuries, which carry the highest severity because of lifelong-care costs.
• Medication and prescribing adverse events — wrong drug or dose, and controlled-substance or professional-conduct issues that also drive board actions.

Contributing Factors: Where Cases Are Actually Won and Lost

The allegation states the theory; the contributing factors decide whether it gets paid. In APP claims the drivers concentrate in the diagnostic process and the supervision relationship. (One methodological note: the CNA/NSO data reports distributions by diagnostic-process step rather than the classic contributing-factor codes, so the percentages below are process-step shares.)

• Diagnostic / lab-testing process failures — about 59.3% of NP diagnosis-related claims, in the failure to order or to obtain and address results. This is the dominant lever.
• Clinical judgment — diagnostic decision-making failures concentrated in test ordering and result interpretation, including cognitive bias and premature closure.
• History and physical / patient-assessment deficiencies — about 19.8% of diagnosis claims.
• Referral and consultation-management failures — about 15.1% of diagnosis claims, and the highest-severity sub-category.
• Communication and follow-up gaps — failure to follow up on abnormal results; the patient-follow-up step appears in about 5.8% of claims.
• Supervision and collaboration gaps — the distinctly APP factor. The Candello data emphasizes inadequate physician oversight of APPs in high-complexity and procedural cases, and it is part of why co-defendant cases pay more.
• Documentation deficiencies, which compound both board defense and civil liability exposure.

What Separates a Strong Case From a Weak One

Both sides converge on two questions an APP case adds on top of the usual diagnostic-error analysis: was the diagnostic process broken in a documented way, and what was the supervision relationship?

Was the dominant failure mode present — and documented?

The strongest APP diagnostic case is the cleanest: an indicated test that was never ordered, or an abnormal result (chest x-ray, PSA, mammogram, abnormal lab) that came back and was never acted on, followed by a "cannot-miss" condition. Because roughly 59% of these claims turn on that exact test-ordering or result-follow-up failure, screen for it first. A documented closed loop — test ordered, result reviewed, action taken — is the defense; a lost or unordered result is the plaintiff's case. A clear causation chain linking the unordered test or unactioned result to the eventual harm is what a viable APP diagnostic case must build.

What was the supervision and collaboration relationship?

This is the lever unique to APP cases, and it cuts in two directions. For plaintiff counsel, an inadequately supervised APP handling a high-complexity, procedural, or pediatric/neonatal case — with a supervising physician who should have been involved — supports naming the physician as a co-defendant and raises the value of the whole case. For defense counsel, documented, appropriate collaboration with a low threshold to escalate is a meaningful shield. Either way, the supervision and escalation record should be pulled and analyzed early.

Does the certificate of merit require a same-profession expert?

This is a procedural trap specific to non-physician defendants. In a number of jurisdictions, when the defendant is a nurse practitioner or physician assistant, the merit affidavit (and the eventual standard-of-care expert) must come from that same profession rather than a physician. Retain a distinguished physician expert against an NP defendant in the wrong state and you may be litigating your own expert's qualification under a dismissal motion. Confirm the expert match against the controlling statute before you retain — and remember that the same specialty-and-reliability questions resurface later as a Daubert and FRE 702 challenge.

And what is the realistic value, co-defendants included?

An APP-only claim with a modest median can become a substantially larger exposure once a co-defendant physician and an institution are in the case. Run the realistic damages picture with the full defendant set in mind — our damages calculator helps frame exposure so neither side prices an APP case on the solo-provider median when the co-defendant dynamic is in play.

Bottom Line

Nurse practitioners and physician assistants are named in a small share of cases and carry modest per-provider severity, but APP claims are their own category. They are overwhelmingly diagnostic, and roughly 59% turn on a single failure mode: a test that was never ordered or a result that was never acted on. Two questions then decide value: was that diagnostic-process failure documented, and what was the supervision relationship — because an inadequately supervised APP in a co-defendant posture raises the value of the whole case. Add the same-profession expert requirement that several jurisdictions impose on non-physician defendants, and the APP case rewards careful, early screening more than almost any other.

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