Blood tests, decoded. A blood result is a number, and it only means something when it is read alongside the person it came from, the conditions under which the sample was taken and that person’s earlier results.
results from healthy people fall outside the reference range by chance.
of mildly raised TSH results were normal when repeated, without treatment.
average fall in testosterone after a sugary drink, which is why the test is done fasting.
Most people have had a blood test come back “normal” while they still feel far from normal, or had one result flagged in red and spent a week worrying about it. Both experiences have the same cause. A single set of results, read in a short appointment, is like looking into a mansion through a keyhole. You can see something, but you cannot get a feel for the whole house.
A reference range usually covers the middle 95 per cent of healthy people, so about one healthy result in twenty falls outside it by chance. Run twenty tests on a perfectly healthy person and the chance of at least one flag is about two in three. A flag is a reason to look more closely, not a diagnosis.
Chance that at least one result is flagged in a healthy person. The more tests in a panel, the more likely a healthy person is to have a result flagged by chance.
The reverse is also true. Your own values usually sit in a narrow band inside the range, so a result that has climbed from the bottom of the range to the top can be a meaningful change while still being “normal”. That is why we compare each result with your earlier ones, and why tests repeated over time tell you far more than a one-off.
Ferritin reflects iron stores, but it also rises with inflammation, infection, hard training, alcohol and fatty liver. A ferritin below about 30 micrograms per litre usually means iron deficiency, but inflammation can make low stores look normal, so ferritin should always be read with CRP and transferrin saturation. A high ferritin worries people, yet about nine in ten raised results come from inflammation, alcohol, fatty liver or weight gain rather than inherited iron overload. The useful test for that condition, haemochromatosis, is a fasting transferrin saturation, and genetic testing is warranted when it is persistently 45 per cent or higher.
Reading ferritin with CRP and transferrin saturation.
HbA1c reflects average blood sugar over about three months, and in Australia a result of 6.5 per cent or more diagnoses diabetes. Because it depends on red cells, iron deficiency can raise it without any change in blood sugar, so it should be read with the blood count and iron studies. Fasting insulin is popular, but it is not standardised between laboratories, and the RACGP advises that it has no routine role.
What builds plaque in the arteries is the number of particles carrying cholesterol into the artery wall. Each particle carries one molecule of a protein called ApoB, so an ApoB result is in effect a particle count, and it reflects risk better than LDL cholesterol. Lipoprotein(a), which is almost entirely inherited, should be measured once in every adult. A level of 125 nmol/L or more raises cardiovascular risk, and a high result is a reason to test your parents, siblings and children.
Two people with the same LDL cholesterol can carry very different numbers of particles. There is one ApoB molecule on every particle, so ApoB counts the particles.
TSH, the thyroid screening test, varies with the time of day, with age and after an illness. In a study of more than 400,000 people, 62 per cent of mildly raised TSH results were normal when repeated, without any treatment. The right step is to repeat TSH with free T4 before starting a tablet that may be taken for life. Biotin, found in many hair and nail supplements, can make a normal thyroid look overactive, so it should be stopped for three days before testing.
Testosterone peaks in the early morning, and in one study a sugary drink lowered it by an average of 25 per cent. A reliable result therefore needs a fasting sample taken before about 10 am, confirmed on a second occasion and read with SHBG, the protein that carries most testosterone in the blood, because a man with low SHBG can have a low total testosterone and a normal amount of active hormone. When testosterone is low, LH shows why. When LH is high, the brain is shouting at the testes to make more, and they are not responding. A low or normal LH means the signal itself is weak. That pattern is far more common, and it is often driven by weight, poor sleep, alcohol or previous steroid use.
LH shows where the problem sits when testosterone is low.
In healthy men who were not used to weightlifting, one hour in the gym raised liver and muscle enzymes for at least a week. Creatine raises creatinine, dehydration concentrates the blood and a recent cold raises ferritin and CRP. Good testing starts with a question, takes the sample under the right conditions and repeats a sensible set of tests over time. The aim is to account for bad luck and catch it early, so that a change shows up as a trend long before it becomes a problem.
A 52-year-old woman’s ferritin is 180, flagged as high, and she has read about haemochromatosis. Her transferrin saturation is 22 per cent, her CRP is mildly raised after a cold, her ALT is slightly high and her waist has grown over two years. Read alone, the ferritin suggests iron overload. Read together, the normal transferrin saturation makes that unlikely, and the pattern points to inflammation and early fatty liver. The plan is to repeat the tests fasting in six to eight weeks and assess her liver and metabolic health, not to order a genetic test.
At My Performance Doctor, your doctor walks you through every set of results on a short video, marker by marker, and compares each with your previous results, your symptoms and your goals. If you have a folder of results that nobody has properly explained, a call with Robyn is a good place to start.
This article is general information and is not a substitute for individual medical advice. From the doctors at My Performance Doctor.