Diagnosis code lookup
What the code on your sick note, referral or discharge letter means — 22 of the most common ICD-10 diagnosis codes explained in everyday words.
This is general information to help you read a code, not a diagnosis or medical advice. Only a qualified doctor can tell you what a code means for your health. If you feel unwell or worried, contact a health professional.
How diagnosis codes work
When a clinician writes a diagnosis, they often record it as an ICD-10 code — a short letter-and-number label from a standard international list. The letter marks a broad chapter (for example, J for the airways, I for the heart and circulation, F for mental health) and the numbers narrow it down. Codes let hospitals, insurers and researchers speak the same language, but they are deliberately brief, so a code on its own never captures your whole picture.
Below are common codes explained in plain words. Pick one to see what it generally refers to.
Common codes
J06.9 — Common cold / upper respiratory infection
A general code for an infection of the nose, throat or sinuses — usually a common cold.
I10 — High blood pressure (essential hypertension)
Raised blood pressure with no single underlying cause identified.
E11 — Type 2 diabetes
The common, adult-onset form of diabetes, where the body handles blood sugar poorly.
M54.5 — Low back pain
Pain in the lower back — one of the most common reasons people see a doctor.
F41.9 — Anxiety disorder (unspecified)
Ongoing anxiety that affects daily life, without a more specific label.
K21.9 — Acid reflux (GERD) without inflammation
Stomach acid coming back up into the gullet, causing heartburn.
J45.9 — Asthma (unspecified)
A long-term airway condition causing wheeze, cough and breathlessness.
J20.9 — Acute bronchitis
A short-lived infection of the airways below the throat, with a cough.
J02.9 — Sore throat (acute pharyngitis)
Inflammation of the throat causing pain, especially on swallowing.
J03.9 — Tonsillitis (acute)
Inflamed tonsils, with a sore throat and often fever.
N39.0 — Urinary tract infection
An infection somewhere in the urinary system, often the bladder.
R51 — Headache
Head pain recorded as a symptom, not a specific diagnosis.
R10.4 — Abdominal pain (unspecified)
Tummy pain recorded as a symptom while a cause is worked out.
M25.5 — Joint pain
Pain in a joint, recorded without naming a specific disease.
E78.5 — High cholesterol / blood fats
Raised fats in the blood, such as cholesterol.
G43.9 — Migraine (unspecified)
A recurring, often one-sided headache that can be disabling.
F32.9 — Depressive episode (unspecified)
A period of low mood and loss of interest affecting daily life.
J11.1 — Influenza (flu)
The flu, causing fever, aches and tiredness, with the virus not identified.
B34.9 — Viral infection (unspecified)
A viral illness where the exact virus and site are not specified.
R05 — Cough
A cough recorded as a symptom on its own.
E66.9 — Obesity (unspecified)
A body-weight range that raises long-term health risk.
Z00.0 — Routine health check
A general check-up, not an illness at all.
Source: Codes from the WHO International Classification of Diseases, 10th revision (ICD-10). Descriptions here are paraphrased into plain language, not the official WHO titles. · checked 2026-09-04
Frequently asked questions
What is an ICD-10 code?
ICD-10 is the World Health Organization's International Classification of Diseases, 10th revision — a shared list of codes doctors and hospitals use so a diagnosis reads the same everywhere. A code like J06.9 is just a shorthand label, not a full description of your health.
Does the code tell me how serious it is?
No. A code names a category; it says nothing about severity, cause or what happens next. Two people with the same code can have very different situations. Only the doctor who wrote it can explain what it means for you.
Why does my note say "unspecified"?
Many codes end in a general "unspecified" category, used when a precise sub-type has not been recorded — often because it is not needed for your care, or is still being worked out. It does not mean anything is being hidden.
Can I use this to diagnose myself?
No. This is a plain-language glossary to help you read paperwork, not a diagnostic tool. If you are worried about a code or a symptom, speak to a doctor or pharmacist.
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