ICD-10 Code K59.00: Constipation, Unspecified

QUICK ANSWER

• What Is ICD-10 Code K59.00? K59.00 is the billable ICD-10-CM code for constipation, unspecified, used when the provider documents constipation without identifying a specific type or cause. It is valid for HIPAA transactions in the FY2026 ICD-10-CM code set.
• When to use it: Apply K59.00 when constipation is documented but no type or cause is specified. Refine to a specific K59.0 code when the record supports it.
• Why it is on a radiology claim: Constipation is a common reason imaging is ordered. The diagnosis is what justifies the exam to the payer, not what the radiologist treated.
• What it pairs with: Most often an abdominal X-ray (KUB), or a combined CT of the abdomen and pelvis when obstruction or another cause is suspected.

What K59.00 Means and When to Use It

K59.00 stands for constipation, unspecified. Use it when a provider has documented constipation and the record does not specify a type, such as slow transit or chronic idiopathic, or an underlying cause, such as medication. It is appropriate as an initial code when constipation is first noted and the detail is not yet available, and it should be refined to a more specific code when the documentation supports one.

It should not be used for conditions where constipation is only a symptom of a distinct entity. Irritable bowel syndrome with constipation (K58.1) and intestinal obstruction (K56.-) are separate diagnoses with their own codes, not K59.00.

Is K59.00 Billable in 2026?

Yes. K59.00 is a valid ICD-10-CM code for HIPAA transactions in the FY2026 code set and can be reported to support medical necessity. The subcategory header K59.0 (Constipation) is not billable on its own and will be rejected if submitted. Always report the full billable code, never the bare subcategory.

The K59.0 Family: Coding to Specificity

When the documentation supports more than “unspecified,” code to the specific type. A specific code tells a cleaner clinical story and supports medical necessity more convincingly. The table below shows the full K59.0 family and its billing status, confirmed against the current ICD-10-CM set.

Note: K59.0 (Constipation) is a non-billable header. Use one of the codes above, never K59.0 by itself.

Why Does a Constipation Code Appear on a Radiology Claim?

This is the part generic constipation pages cannot tell you, because they are not written for imaging billing. A radiologist does not treat constipation. But constipation is a frequent reason a study is ordered, and on the imaging claim the diagnosis is what justifies the exam to the payer. One question we hear constantly from imaging practices is why a GI diagnosis is sitting on their claim at all; the answer is that the ordering indication, not the treatment, drives medical necessity for radiology.

A documented constipation indication commonly supports an abdominal X-ray to evaluate stool burden and bowel gas pattern, and in some cases a CT of the abdomen and pelvis when obstruction or another cause is suspected. The imaging is reported with the appropriate procedure code, and a diagnosis like K59.00, or a related symptom code such as abdominal pain, R10.30, is what links the study to a covered clinical reason. Payers, including Medicare, require the ICD-10 diagnosis to support medical necessity for the imaging, and a study whose ordering diagnosis does not justify it is a denial waiting to happen.

Across the billing companies we vet, a recurring pattern is imaging claims lost not to a coding typo but to an ordering diagnosis that never supported the exam in the first place. That is the practical reality for an imaging practice: the diagnosis code is not paperwork, it is the difference between a paid claim and a written-off study.

What Abdominal Imaging Does K59.00 Support?

When constipation is the indication, these are the imaging codes the diagnosis most often supports. Select the code that matches the study actually performed.

Two rules that prevent denials on these studies. First, select only one abdominal X-ray code per encounter based on the number of views, never two. Second, when both the abdomen and pelvis are scanned, use the combined CT codes, and see CT abdomen and pelvis, CPT 74176 for the without-contrast detail; billing the abdomen and pelvis separately is improper. Remember that oral or rectal contrast does not make a CT a “with contrast” study, so a patient who only drinks contrast is coded without contrast (74176). For appropriateness of the study itself, the American College of Radiology guidelines are the standard reference.

Common K59.00 Coding Mistakes

The most common issue we see across imaging practices is a diagnosis that does not actually justify the study billed. These are the errors that most often turn a K59.00 claim into a denial:

• Defaulting to K59.00 when the record documents a specific type, such as slow transit (K59.01), drug induced (K59.03), or chronic idiopathic (K59.04) constipation.
• Submitting the non-billable header K59.0 instead of a complete code.
• Linking an abdominal imaging study to a diagnosis that does not support medical necessity for the exam.
• Using K59.00 for a distinct condition where constipation is only a symptom, such as IBS with constipation (K58.1) or intestinal obstruction (K56.-).
• Billing two abdominal X-ray codes for a single encounter instead of choosing one by view count.
• Coding a CT as “with contrast” when only oral or rectal contrast was given.

ICD-10-CM and CPT codes are maintained under CMS, the National Center for Health Statistics, and the American Medical Association, and are provided here for reference. Coding must follow provider documentation, and payer medical-necessity rules vary, so verify against current guidelines and local coverage determinations.

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