HOME HEALTH TESTS: WHAT’S WORTH IT, WHAT’S NOT?

Can you trust a screening test you can do from the comfort of your own home? Dr Sarah Jarvis gives her take and explains the pros and cons

Dr Sarah Jarvis on the pros and cons of self-testing

Since the start of the Covid-19 pandemic, many of us have taken our health into our own hands as health services have become less accessible, or we’ve been worried about visiting the GP’S surgery. As a result, there has been a surge in interest in home health tests.

Screening has no downsides, right? Wrong. As a medical student, it was drummed into me that the key criteria for any test are that it should be easy to perform and interpret, acceptable, accurate, reliable, sensitive and specific.

‘Sensitive’ refers to how many people with a condition the test picks up. Ideal, of course, is 100% sensitivity – it picks up everyone with a condition. Tests telling someone who has a condition that they are free of it are called ‘false negatives’. ‘Specific’ relates to the opposite – ‘false positives’ tell someone they’re affected when in fact they’re disease-free.

Many genetic home tests will tell you your risk is increased, but not by how much in real terms. If you’re four times more likely than anyone else to get, say, breast cancer, that’s a huge increase, because lots of women get breast cancer – one in eight will get it during their lifetime. If you have a BRCA1 gene mutation, you have a two in three risk of getting breast cancer by the age of 70. If you’re found to be BRCA positive, you may take preventive action, such as taking tamoxifen, having a mastectomy or having your ovaries removed. But this would be done after careful counselling with your specialist team.

If, on the other hand, a test revealed you were four times more likely to get sinus cancer, you’d be understandably worried. But since this cancer is so rare, affecting just one in 400,000 people a year, a four-fold increase still means a 99.99% chance of you never getting it. There’s nothing dramatic you can do to prevent it (apart from not smoking),

yet you’d live with the knowledge that you’re ‘at risk’. This can lead to depression, anxiety or guilt that your family is at risk from your ‘tainted’ genes.

Genetic home tests

One problem with home genetic tests is interpretation. They often provide limited information about inherited conditions; they won’t tell you if you’ll get it for certain, how severe your symptoms might be, or how they might progress. There are no preventive strategies for many disorders they highlight, so there is little or nothing to gain by knowing.

The internet is awash with offers of tests promising personalised strategies to lose weight, exercise more effectively and boost energy levels based on your genes. Genetic testing can be extremely accurate for certain conditions caused by a single defective gene, such as Huntington’s disease. But energy, weight and many other conditions are influenced by multiple genes. In addition, one study* suggested that 40% of results where customers were told their genes put them at higher risk were false positives.

Blood pressure monitoring

Home blood pressure monitoring can give a better idea of your blood pressure than a single measurement at your GP’S surgery. However, don’t rely on a single reading or panic if one reading is high.

Choose a clinically validated digital machine with an upper arm cuff – your pharmacist can advise. Sit quietly for five minutes before you measure your blood pressure, with both feet flat on the floor, back supported and arm at 45 degrees. Take three readings, one to two minutes apart, and use the average (unless the first is much higher, in which case ignore it). Do this twice a day for eight days but ignore the first day’s readings. If your average is below 135/85, your blood pressure is under control. If you’re on medication, you can use this to avoid a GP visit, as they will accept this reading.

Food intolerance and allergy tests

There are two main kinds of food allergy, both caused by an overreaction by the immune system. The most serious is due to IGE antibodies, which react with foods (common culprits are peanuts, brazil nuts, eggs, sesame and shellfish), causing very rapid onset of symptoms including wheezing; swelling of the lips, tongue and throat (which can block airways); an itchy, raised rash; faintness, palpitations and breathlessness; diarrhoea and tummy pain; and confusion or collapse. Sufferers must be referred to an allergy clinic for diagnosis and treatment and carry an adrenaline injection pen. This is not something you want to test at home.

Non IGE allergic reactions are usually less serious, but symptoms include eczema, tiredness, reflux, diarrhoea, constipation and poor growth in children. Non IGE cow’s milk allergy is common in children and, although they usually grow out of it, it needs medical input.

Food intolerance isn’t anything to do with the immune system and isn’t life-threatening, but can cause wind, bloating, diarrhoea, tiredness, headaches and itchy skin rashes. Many companies and unqualified nutritionists offer vega testing, hair analysis, IGG blood tests or kinesiology (among others) to ‘diagnose’ food allergies or intolerance. There’s no evidence they’re accurate and the National Institute for Health and Care Excellence (NICE) recommends avoiding them.

DIY Covid tests

It’s hardly surprising there has been an explosion in the number of tests taken for Covid-19 – swabs to test whether you are currently infected, and antibody blood tests to see if you’ve had it in the past.

A few months ago, the government talked of ‘Covid passports’ to allow people who’d had the infection to mingle freely, on the basis that they were immune. However, we simply don’t know if having antibodies makes you immune (you may not have enough to offer full protection) and, if so, how long immunity will last.

Blood tests for antibodies, using a Public Health England-approved test and interpreted at an approved laboratory, are at least 99% specific and up to 98% sensitive, depending on how long after infection you take the test. Many pharmacies now offer this test privately. ‘Rapid access’ home finger-prick tests haven’t shown the same levels of accuracy and are not recommended.

If you do take an antibody test through your pharmacy, don’t rely on the result to assume you’re immune. It may confirm if you’ve had Covid, but not whether you could get it again.