Nailfold capillaroscopy: what the test shows in Raynaud's and connective tissue disease

Capillaries are the smallest blood vessels in the body. At the base of the fingernail they sit close to the surface, and this makes them accessible to a specialised microscope. Arthritis UK describes the test as one that involves looking at the tissue from a fingernail under a microscope, so doctors can look closely at the small blood vessels in the fingers. It is called nailfold microscopy or capillaroscopy.

The test is not described as painful in the sources used for this guide, and this page does not make claims about how it feels or how long it takes, because the pages read do not say. Ask the department carrying it out what to expect, including whether you should avoid nail polish or hand cream beforehand.

Raynaud's phenomenon is where blood stops flowing properly to the fingers and toes, usually in response to cold or stress. The NHS says the skin may turn white or paler, sometimes blue, and then red as blood flow returns, and that pain, numbness and pins and needles can occur. Attacks can last from a few minutes to a few hours.

Most Raynaud's is primary, which means it occurs on its own. Arthritis UK says primary Raynaud's is fairly common, affects more women than men and does not usually damage the fingers. Secondary Raynaud's is linked with another condition, most often scleroderma and less commonly lupus, and can be more severe, with ulcers at the fingertips in rare cases. Because the symptoms can look the same, doctors need ways of separating the two groups, and capillaroscopy is one of them.

Arthritis UK sets out several tests that may be carried out if Raynaud's is suspected and the diagnosis is in doubt. They are done to tell the primary and secondary forms apart, and they may need to be done at a hospital.

Scleroderma is the name the NHS gives to a range of autoimmune conditions that can cause hard, thickened areas of skin and sometimes problems with muscles, bones, internal organs and blood vessels. The two main types are localised scleroderma (morphoea) and systemic sclerosis. Limited cutaneous systemic sclerosis often starts as Raynaud's, according to the NHS, which is why Raynaud's that begins in adulthood or comes with other features gets a closer look.

The NHS advises seeing a GP if Raynaud's symptoms are very bad or getting worse, if they affect only one side of the body, if you also have joint pain, skin rashes or muscle weakness, if you are over 30 and get symptoms for the first time, or if a child under 12 has symptoms. A GP may arrange tests if Raynaud's could be a sign of a condition such as rheumatoid arthritis or lupus.

Arthritis UK reassures that if you have scleroderma it is likely you will get Raynaud's at some stage, but that having Raynaud's does not mean you will develop scleroderma or another connective tissue disease. It encourages getting a diagnosis early to find out whether Raynaud's is primary or secondary.

Results are interpreted alongside your symptoms, examination and blood tests rather than on their own. Arthritis UK says your doctor will make a diagnosis based on your symptoms and the results of any tests. The sources read for this guide do not describe the specific patterns doctors look for on capillaroscopy, so this page does not either; a rheumatologist can explain what was seen in your own report.

Whatever the result, self-care is similar. The NHS suggests keeping your home warm, wearing warm clothes especially on the hands and feet, avoiding sudden changes in temperature, exercising regularly, not smoking and not having too much caffeine. A GP may prescribe a medicine such as nifedipine to improve circulation if symptoms are very bad or getting worse, and Arthritis UK describes drugs that widen blood vessels, with intravenous treatment reserved for severe cases, almost always secondary Raynaud's.

On the NHS, a GP who suspects secondary Raynaud's may arrange tests, and Arthritis UK says some of them may need to be done at a hospital. Private rheumatology services may also offer tests and consultations, and a private specialist will usually want to see any earlier blood results and reports. Whichever route you use, ask for a written report that you can bring to any later appointment.