Raynaud's phenomenon and blood tests

What the research found.

• One study looked at the nailfold vessels of 759 consecutive people with Raynaud's. Results were normal in 354, nonspecific in 159, and showed a scleroderma pattern in 246. The absence of that scleroderma pattern had a negative predictive value of 88 percent, while positive predictive values were low.

  Van Roon and colleagues, The Journal of Rheumatology, 2019

• One study ranked the parts of that scan against each other to see which did most. Capillary loss separated systemic sclerosis from other causes of Raynaud's best, at an area under the curve of 0.905, from 0.869 to 0.942. Dilatation reached 0.863 and giant capillaries 0.835, while branching vessels reached only 0.604.

  Bournia and colleagues, Clinical and Experimental Rheumatology, 2020

• One study compared 190 people with antisynthetase syndrome against 75 with primary Raynaud's. Capillaroscopy abnormalities appeared in 62.1 percent of the first group. They also appeared in 29.3 percent of the primary Raynaud's group, at P under 0.001.

  Sebastiani and colleagues, The Journal of Rheumatology, 2019

• One study measured cryoglobulins in 1183 people referred for hand-arm vibration assessment. Eleven of them were positive, which is 1 percent, and seven of those were at a low level. Among 795 people tested for cold agglutinins, not one came back positive, and its authors conclude that routine testing isn't recommended.

  Alsaidi and colleagues, Occupational Medicine, 2022

• One study took 1600 nailfold images from 50 young people. A scleroderma pattern was more frequent in juvenile systemic sclerosis than in primary Raynaud's, at P under 0.001. The two measures that separated those groups were reduced capillary density, at P under 0.001, and the presence of giant capillaries, at P equals 0.01.

  Binda and colleagues, Clinical and Experimental Rheumatology, 2026

What the number means.

One test does most of the work

When somebody has Raynaud's, one question sits underneath all of it, which is whether this is on its own or the first sign of something else. One test answers that better than the rest. It's called nailfold capillaroscopy, and it's a magnified look at the tiny blood vessels at the base of your fingernail.

It takes only minutes and it doesn't hurt at all. What it looks for is a particular appearance that is associated with a group of connective tissue diseases. That appearance is called the scleroderma pattern, and it's what every number below is about.

What the scan does well

One study looked at the nailfold vessels of 759 consecutive people with Raynaud's, and it sorted the results three ways. They were normal in 354 people, nonspecific in 159, and showed a scleroderma pattern in 246. The useful figure from that study is what a normal result rules out.

The absence of a scleroderma pattern had a negative predictive value of 88 percent. That's a strong result for a test that takes only minutes, and it means something quite specific. If your scan shows no scleroderma pattern, the odds that you have one of those diseases are low, though they aren't zero.

A test that answers one direction well is still a good test to have. This one answers the direction that most people are asking about. That direction is whether something else is going on underneath the Raynaud's, which is the question people come in with.

What the scan does badly

That study reported the other direction too, and it comes out much weaker. Positive predictive values were low, and the reason is that the appearance isn't specific to any one disease. That pattern appeared in 88 percent of people with systemic sclerosis, 71 percent of those with mixed connective tissue disease, and 33 percent with primary Sjogren's syndrome.

It reached 17 percent with lupus and 13 percent with rheumatoid arthritis. So an abnormal scan points toward a whole family of diseases rather than at any one of them. It's the start of a conversation rather than the end of one.

There's a second reason to hold an abnormal result loosely, which is that plenty of people with ordinary Raynaud's have one. That's what the next section of this page is about. The overlap between the two groups is larger than most people expect it to be.

Abnormal scans in ordinary Raynaud's

One study compared 190 people with antisynthetase syndrome against 75 people who had primary Raynaud's instead, where primary means Raynaud's on its own. There's no underlying disease behind that one. Scan changes appeared in 62.1 percent of the antisynthetase group.

They appeared in 29.3 percent of the primary Raynaud's group, and the difference was real, at P under 0.001. Read that second figure just as closely as the first one. Nearly three in ten people with plain Raynaud's had something abnormal on that scan, so a scan change can't sort one group from the other.

That overlap is the reason a scan gets read alongside everything else that's known about you. On its own it narrows the question rather than answering it, which is a real contribution even so. Your team is doing that reading whether or not anybody says so.

Not every part of the scan is worth as much

One study ranked the parts of that scan against each other, and it asked one question of all of them. Which one best separated systemic sclerosis and its relatives from other causes? Capillary loss did best, at an area under the curve of 0.905, from 0.869 to 0.942.

Dilatation came next at 0.863, from 0.818 to 0.907, and giant capillaries reached 0.835, from 0.787 to 0.884. Two of the measures did a good deal worse than those. Micro-bleeds reached 0.720, from 0.662 to 0.779, and branching vessels reached 0.604, from 0.539 to 0.670.

Here's the scale those figures are on. A perfect test scores 1.0 and a test no better than a coin toss scores 0.5. So capillary loss is doing real work and branching vessels are barely doing any at all.

One study in young people found those two measures being notable again, which counts for something, because the test gets used in teenagers too. It took 1600 images from 50 people with an average age of 16.4 years. Reduced capillary density and giant capillaries were what separated juvenile systemic sclerosis from primary Raynaud's.

Two blood tests that aren't worth doing

Most of this site is about what the tests show, and this part of it is quite different. It's about two of them that mostly show nothing at all. One study measured cryoglobulins in 1183 people who had been referred for hand-arm vibration assessment.

Those are proteins in the blood that clump together in the cold, so the idea behind testing is obvious enough. Eleven of them came back positive, which is 1 percent, and seven of those were at a low level. It tested 795 of those people for cold agglutinins, and not one was positive.

That's a zero out of 795, which is the sort of result that settles a question. Its authors draw the conclusion directly, saying routine testing for cryoglobulins and cold agglutinins isn't recommended in patients with these symptoms. Those are their own words rather than ours at all.

That study was done in an occupational vibration clinic rather than in a general Raynaud's clinic, which counts for something. So read it for that setting first, before taking it anywhere else at all. It's still the clearest statement this site holds anywhere that a test can be not worth doing.

What the sources here don't cover

One standard test is missing from this page, and it's the antinuclear antibody, because our set holds nothing measuring it in this population. A positive antinuclear antibody is often what decides whether a nailfold scan gets done at all. So its absence here is genuinely missing evidence rather than an oversight.

This site holds sources on that test in blood donors and in rheumatology referrals, and neither one describes a group of people with Raynaud's. So this page gives no figure for it anywhere. That absence is recorded for the physician review rather than papered over with something plausible. A visible hole is more use to you than a confident sentence with nothing behind it.

What to do with a result

Ask whether a nailfold scan has been done, because it's the most useful single test here and it takes only minutes. If it has already been done, ask which of the three categories your result fell into. A normal result is worth taking as real reassurance, and an abnormal one is a reason to keep looking and not an answer.

Then report the things that change the question being asked about you. New ulcers on the fingers count, and so do new skin changes, and so does new trouble swallowing. Nothing on this page tells you what your own result means, and it was never meant to. What it tells you is how these tests behave across hundreds of people, and your team puts that together with your history and your examination.

Common misconceptions.

Cautions specific to this condition.

• Ask whether a nailfold scan has been done. It's the single most useful test in this situation and it takes minutes.
• Take a normal scan as real reassurance. Its negative predictive value was 88 percent in a study of 759 people.
• Don't take an abnormal scan as a diagnosis. Positive predictive values were low, and scan changes appeared in 29.3 percent of people with plain Raynaud's in another study.
• Ask what a blood test is for before agreeing to it. Cryoglobulins came back positive in 1 percent of one referred group, and cold agglutinins in zero of 795.
• Report new finger ulcers, skin changes, or swallowing trouble. Those move the question from ordinary Raynaud's toward something that needs more looking at.
• This page gives no reference range and no threshold. What your own result means is your team's call. They read it alongside your history and your examination.

Questions patients ask.