Possibly one of the biggest indicators towards our profession’s tendency to over-diagnose and over-treat patients is the prevalence of so called Vitamin D deficiency, Anaemia, Folate deficiency, and Hypothyroidism among others. The likely culprit in this is the ubiquitous use of blood tests, poor interpretation of the results, and the increasing practice of DIY screening.
Possibly one of the most common presentations seen in medicine is ‘Tired all the time (TATT)’. TATT most commonly comes from poor lifestyle, lack of exercise, inactivity, poor diet, everyday stress, and poor personal action; yet most patients with this symptom prefer to believe there is a medical cause.
In my opinion, TATT alone (like many other solitary symptoms) is not an indicator for blood tests without further signs of a medical cause, and tests should then only be used as an adjunct to a working diagnosis based on history and clinical examination. Sadly, there are far too many of us who believe ‘screening for the cause’ is a viable option, and these patients are sent for a myriad of blood tests in a misplaced attempt to hunt out the cause. This is a fundamentally flawed concept. The ethics of benefit and harm in screening tests is a minefield, and commissioned screening tests such as breast screening and faecal occult blood, are scrutinised regularly and regulated to prevent harm.
In addition, there is a ubiquitous inability of clinicians to correctly interpret the results of these tests despite routinely prescribing them. Two mistakes are common: The first is the misunderstanding of the normal range. Depending on your lab, the normal range for Hb. in a male is about 13.5 to 17.5 grams per decilitre. This means exactly what it states, that anything within this range is normal. A Hb. of 13.5 in not low; it is within the range of normal. So telling the patient their Hb, Folate, thyroid function, Vitamin B,D etc. is at the low end of normal (or just low like a fuel guage), and subsequently treating as a deficiency, or ‘topping it up’ is erroneous and all too common.
Secondly is the misunderstanding (or complete lack of knowledge) of the confidence interval. Most laboratory tests have a 95% confidence interval. This means that 95% of the healthy population will have a blood result within the normal range. Meaning that 5% of healthy people will have a blood result outside of the normal range. That is one in twenty, so, if you send a patient for 20 blood tests the probability is that one of the results will be out of the normal range and you’ll likely use this to make a misdiagnosis. If you use blood tests to screen 1 patient a day with 20 blood results (FBCs, U&Es, and LFTs) in a 5-day working week you will misdiagnose and mistreat on average 260 patients per year. In ED where blood tests are far more commonplace, misdiagnosis and the subsequent inappropriate treatment are likely to be significant.
Blood Test Screening = Overdiagnosis and Overtreatment = HARM.