The SI medical abbreviation most often means suicidal ideation in mental health, emergency and primary care notes, which refers to thoughts about ending one's life. In orthopedics, spine care and physical therapy, SI means sacroiliac, as in the SI joint in the lower back, and in lab reporting SI can mean the International System of Units.
Context decides which meaning a writer had in mind. A psychiatric screening line such as denies SI/HI is clearly about thoughts and safety, while SI joint injection is about the pelvis. This page explains each use in plain, neutral language.
At a glance
Most common meaning
Suicidal ideation (mental health, emergency, primary care)Other meanings
Sacroiliac, as in SI joint (orthopedics, spine); International System of Units (lab values)Often paired with
HI (homicidal ideation), as in SI/HIWhere you see it
Mental status exams, screening notes, spine and therapy notes, lab reportsDo not confuse with
SSI (sliding scale insulin, or surgical site infection)Crisis support
In the US, call or text 988
SI as suicidal ideation in mental health notes
Suicidal ideation means thoughts of ending one's life. Clinicians ask about it routinely in emergency departments, psychiatric care, primary care and many hospital admissions, because asking directly is a standard part of a safety assessment. Asking does not put the idea in someone's mind; it opens the door to support.
Notes often describe the type of thoughts. Passive SI refers to wishing not to be alive without a plan, while active SI involves thoughts of acting. Clinicians also record whether there is a plan, intent or access to means, and protective factors such as family, faith or future goals.
Reading SI/HI in a mental status exam
The pairing SI/HI is so common that many notes include it even when everything is normal. HI stands for homicidal ideation, thoughts of harming others.
| Line in the note | Plain meaning |
|---|---|
| Denies SI/HI | Reports no thoughts of suicide or of harming others |
| Passive SI, no plan or intent | Some thoughts of not wanting to be alive, without a plan or intent to act |
| Endorses SI | Reports having suicidal thoughts |
| Safety plan reviewed | Coping steps and contacts were gone over with the patient |
Words like endorses and denies are standard charting language. They record what the person reported, not a judgment about them.
SI joint: the orthopedic meaning
The SI joint medical abbreviation refers to the sacroiliac joints, which connect the base of the spine, the sacrum, to the pelvis on each side. They are a known source of lower back and buttock pain. Notes in spine, pain and therapy clinics use SI in this sense, for example R SI joint tenderness or SI joint dysfunction.
Physical therapy note: Pain over L SI joint, worse with stairs, provocation tests positive. The therapist means the left sacroiliac joint is tender and that certain movements of the pelvis reproduced the pain.
Related pages cover LBP for low back pain and MSK for musculoskeletal care.
SI units on lab reports
On lab reports SI refers to the International System of Units, the metric system used by most countries. Glucose, for example, may be shown in millimoles per liter (mmol/L) in SI units instead of milligrams per deciliter (mg/dL). Reports from different countries, or research papers, may list both. This sense rarely appears in bedside notes.
How to tell which SI medical abbreviation is meant
| Clue nearby | Likely meaning |
|---|---|
| HI, denies, endorses, plan, intent, safety | Suicidal ideation |
| joint, pelvis, back pain, injection, sacrum | Sacroiliac |
| units, mmol/L, conversion, conventional units | International System of Units |
Mental health and spine notes rarely overlap, so the section of the chart usually settles it. For other screening and assessment shorthand, see our nursing and chart notes guide, and the MDD page for a related mental health term.
Frequently asked questions
What does SI mean in mental health?
In mental health notes SI means suicidal ideation, thoughts about ending one's life. Clinicians ask about it as a routine part of assessment. People in the US can call or text 988 for round the clock crisis support.
What does denies SI/HI mean?
It means the patient reported no thoughts of suicide and no thoughts of harming others when asked. It is a standard screening line in emergency and mental health notes.
What is the SI joint?
The sacroiliac joint links the lowest part of the spine to the pelvis, with one on each side. It can be a source of lower back or buttock pain, and SI joint is the usual way to write it in orthopedic and therapy notes.
Is SI the same as SSI?
No. SSI is a different abbreviation, usually meaning sliding scale insulin or surgical site infection. SI on its own most often means suicidal ideation or sacroiliac, depending on the setting.