Misdiagnosis & Diagnostic Error Malpractice Claims

Diagnostic error is consistently identified as among the most common and most costly categories of medical malpractice claims — and also one of the most misunderstood. The claim is almost never that a diagnosis turned out to be wrong. It is that the process used to reach it departed from what a careful physician would have done, and that the departure made the outcome worse.

Quick answer: Diagnostic error claims cover failure to diagnose, delayed diagnosis, misdiagnosis, and failure to refer to an appropriate specialist. A wrong diagnosis alone is not malpractice — diagnosis is inherently probabilistic, and the claim turns on whether the differential diagnosis process itself fell below the standard of care: an indicated test never ordered, an abnormal result never followed up on, a red flag never escalated. Causation is usually the hardest part — proving that earlier or correct diagnosis would have led to a materially better outcome, which is exactly where the loss-of-chance doctrine becomes central in missed-cancer cases.

The Four Fact Patterns

Failure to diagnose. A condition was present and detectable, and a reasonably careful workup should have identified it, but it was missed entirely.

Delayed diagnosis. The correct diagnosis was eventually reached, but only after a delay that itself caused harm — a cancer that progressed to a later stage, an infection that spread, a condition that became substantially harder to treat by the time it was identified.

Misdiagnosis. The wrong diagnosis was reached and acted on, leading to treatment that was not just ineffective but affirmatively harmful — treating the wrong condition can mean missing the real one while also exposing the patient to unnecessary risk from treatment they did not need.

Failure to refer. The presenting symptoms warranted escalation to a specialist, and the treating provider proceeded without making that referral — a distinct failure from an error in the provider’s own diagnostic reasoning.

Why Being Wrong Isn’t Enough

Diagnosis is inherently probabilistic. A rare condition can mimic a common one; a common condition can present atypically. A reasonably careful physician, following an entirely appropriate diagnostic process, can still reach the wrong conclusion — and that alone is not malpractice.

What the claim actually requires is a showing that the process itself — not just its outcome — fell below what a reasonably careful physician in the same specialty would have done given the same presenting information. This is exactly why diagnostic error claims are evaluated against the differential diagnosis, not against the final answer.

The Differential Diagnosis: What Actually Gets Scrutinized

The differential diagnosis is the structured process of identifying and systematically ruling out the range of conditions that could explain a patient’s presentation. Claims typically focus on one specific failure within that process:

• An indicated test was never ordered, despite symptoms that would call for it
• An abnormal result was ordered but never followed up on — a genuinely common and often clear-cut failure, since the record shows the information existed and simply was not acted on
• A red-flag symptom was not escalated — a finding that should have triggered a specialist referral, additional imaging, or admission, but did not
• The working diagnosis was never reconsidered when the patient’s condition failed to improve as the original diagnosis would have predicted

Each of these is, in principle, provable directly from the medical record itself, which is why the complete chart — not just the final diagnosis note — is the central piece of evidence in these cases.

Causation: Usually the Real Fight

Even where a diagnostic failure is clearly established, the claim still has to show the delay or error actually made the outcome worse. For a condition that would have been difficult to treat successfully regardless of timing, this can be a genuinely hard showing to make — and it is exactly where the loss-of-chance doctrine, described in our guide to the four elements of a medical malpractice claim, becomes central. States that recognize loss of chance allow recovery for a diagnostic delay that reduced an already-uncertain chance of a good outcome; states that reject it hold claimants to the traditional more-likely-than-not standard, which can defeat an otherwise strong diagnostic-error claim if the patient’s prognosis was already poor.

This is most sharply litigated in missed or delayed cancer diagnosis cases, where the central question is frequently not whether the cancer was missed, but what earlier detection would actually have changed given the specific cancer’s staging and progression timeline — a question that almost always requires oncology-specific expert testimony rather than general causation argument.

Failure to Refer: A Distinct Theory

Where a generalist or primary provider should have recognized that presenting symptoms exceeded their own expertise and referred the patient to a specialist, the failure to make that referral is its own basis for a claim — separate from any flaw in the generalist’s own reasoning. The analysis shifts to whether a reasonably careful generalist, faced with those specific red flags, should have recognized the limits of their own diagnostic competence for that presentation, rather than continuing to manage the case themselves.

The Evidence That Actually Decides These Cases

• The complete chart, including every symptom reported at every visit, not just the ones that made it into a summary note
• Test orders and results, and specifically the timeline between an abnormal result being received and any action taken on it
• Referral records, or their absence, where a failure-to-refer theory is involved
• The standard differential diagnosis for that specific presentation, established through expert testimony
• Staging and progression evidence, in a delayed-diagnosis case involving a progressive condition, showing what changed between when the diagnosis should have been made and when it actually was

Practical Steps

1. Request the complete chart, not a summary, including every test ordered, every result received, and every note from every visit relevant to the diagnosis.
2. Build a timeline of exactly when each symptom was reported, when each test was ordered and resulted, and what happened next at each point.
3. Identify the specific failure — a missed test, an unactioned result, a missed referral, an unreconsidered diagnosis — rather than arguing generally that “something was missed.”
4. Get a qualified expert in the relevant specialty to evaluate whether the diagnostic process, not just its outcome, met the standard of care.
5. Understand whether your state recognizes loss of chance, since it can determine whether a claim survives at all where the underlying condition already carried a poor prognosis.
6. Move quickly. Beyond the ordinary statute of limitations, most states also impose an early certificate-of-merit or expert-report deadline — see our guide to certificate of merit and expert report requirements.

Sources & Further Reading

• National Academy of Medicine, Improving Diagnosis in Health Care (2015) — the landmark report identifying diagnostic error as a persistent and significant patient safety concern
• Herskovits v. Group Health Cooperative of Puget Sound, 664 P.2d 474 (Wash. 1983) — the origin of the loss-of-chance doctrine in a delayed cancer diagnosis, discussed in depth in our four-elements guide
• Restatement (Second) of Torts § 299A — the standard-of-care framework for those undertaking to render services requiring special skill, applicable to diagnostic reasoning
• See our guides to the four elements of a medical malpractice claim for the underlying causation and loss-of-chance framework, certificate of merit and expert report requirements for the early procedural deadline that applies regardless of how strong the diagnostic-error facts are, and informed consent and failure to warn for the separate disclosure-based duty that is often confused with a diagnostic error claim