Blood count

A blood count is the commonest laboratory test of all, and in gynaecology often the most informative. Exhaustion, hair loss, difficulty concentrating, breathlessness on the stairs – all of these regularly lead to a value that can be put right with a tablet. This page explains what a blood count contains, which values matter in gynaecology, and why the haemoglobin value alone is not enough.

What a blood count is

The full blood count counts and measures the cells in the blood: red cells, white cells and platelets. The differential blood count adds a breakdown of the white cells into their subgroups.

It is obtained from a blood sample taken from a vein in the arm. You do not have to be fasting for it; that only applies if blood sugar and blood lipids are being measured at the same time. The result is usually available the same or the next day.

If you have had bad experiences with blood tests, or tend to feel faint during them, it is best to say so beforehand. The sample is then taken lying down, and there is no need to explain yourself – it is a reaction of the nervous system, not a question of how much you can take. Having drunk plenty also helps in finding the veins.

A blood count alone, however, rarely answers a question completely. It shows that something is not right and gives a direction. Which additional values are needed emerges from the conversation – which is why it starts with the question of what is actually troubling you, and not with the form.

The red cells

They transport oxygen. Four values describe them, and their interplay says more than any one of them.

The Hb value is the best known, and a value that is too low means anaemia. What makes it interesting is only its combination with the MCV: small, pale red cells point to iron deficiency, large ones to a lack of vitamin B12 or folate. The same anaemia has a completely different cause and a completely different treatment depending on the MCV.

In pregnancy the Hb value falls as a matter of course, without any disease being present: blood volume increases by around forty per cent, but the number of red cells only by about twenty. The blood is therefore diluted. That is why lower thresholds apply in pregnancy – from about 11 g/dl in the first and third trimester, 10.5 g/dl in the second.

Iron deficiency: the commonest theme

A considerable proportion of all women of childbearing age have too little iron. The cause almost always lies in the same place: monthly bleeding. Iron is lost with every period, and if the bleeding is heavy, more is lost than comes in through food.

The decisive point for the diagnosis: the Hb value only becomes abnormal late. The body empties its stores first while still maintaining blood formation. Anyone measuring only the Hb therefore often finds iron deficiency only once it has already led to anaemia – sometimes years after the symptoms began.

The storage value is called ferritin. It shows how much iron is stored and falls long before the Hb. A ferritin below 30 µg/l counts as deficiency, below 15 µg/l as marked – even with a completely normal Hb. Anyone complaining of exhaustion, hair loss, brittle nails, difficulty concentrating or restless legs should therefore have not only a blood count but a ferritin as well.

One qualification belongs with this: ferritin rises with inflammation and can then mask a deficiency. Where the picture is unclear, CRP is measured alongside it, and occasionally transferrin saturation as well.

Treatment is with iron tablets for at least three months – and then for the same length of time again, to fill the stores. The Hb rises after a few weeks; the ferritin needs months. Iron is best absorbed on an empty stomach together with vitamin C; coffee, tea and dairy products inhibit absorption considerably. Anyone who cannot tolerate tablets, or whose losses are too great, is given iron as an infusion.

The most important question, however, remains the cause. Iron deficiency due to bleeding that is too heavy is not put right by topping up the iron – the bleeding itself needs investigating and treating. Fibroids, polyps, adenomyosis or a thyroid disorder are the commonest causes, and all four are treatable. The hormonal coil is one of the most effective options here, because it directly reduces how heavy the bleeding is.

The white cells

They are the immune defence. The normal range is about 4,000 to 10,000 per microlitre. Raised values point to a bacterial infection, to inflammation or to treatment with steroids; low values to a viral infection or – rarely – to a disorder of blood formation.

Here too pregnancy is a special case: white cells are routinely raised, often to 12,000 to 15,000, and considerably higher during labour. Such a value alone is therefore no indication of infection. It is assessed together with the CRP and the clinical picture.

The differential count breaks things down further: neutrophils with bacterial infections, lymphocytes with viral ones, eosinophils with allergies and parasites. This breakdown is not requested routinely, but where there is a specific question.

The platelets

They are responsible for stopping bleeding; the normal range is 150,000 to 400,000 per microlitre. In pregnancy they fall slightly – in about one woman in ten below 150,000, without anything following from it. This is called gestational thrombocytopenia and is harmless.

They become important in the third trimester for a different reason: a marked fall can be part of HELLP syndrome, a severe form of pre-eclampsia. Raised liver values and changes in the blood count come with it. That is why, with high blood pressure or upper abdominal pain in pregnancy, blood count and liver values are measured together – and why upper abdominal pain in late pregnancy is always a reason to ring the same day.

What else is measured in pregnancy

The Eltern-Kind-Pass provides for two major blood tests. The first takes place by the end of the 16th week, the second between the 24th and 28th week.

The blood group with rhesus factor is more than a formality. If the mother is rhesus negative and the baby rhesus positive, she can form antibodies against the baby’s blood – usually without consequence in this pregnancy, but dangerous in the next. That is exactly what anti-D prophylaxis prevents: an injection around the 28th week and another after the birth. It is the reason rhesus incompatibility has practically disappeared today.

The glucose tolerance test looks for gestational diabetes. You come fasting, a fasting measurement is taken, then you drink 75 grams of glucose in water, and measurements are repeated after one and after two hours. It therefore takes at least two hours and is done by appointment at a laboratory; some GPs offer it as well. An abnormal result is no disaster: four women in five manage with a change of diet alone.

When these examinations fall due in your pregnancy is worked out by the maternity passport planner.

Blood counts in the menopause

In the menopause the focus of interest shifts. Bleeding often becomes heavier and more irregular at first before it stops altogether – that is the phase in which iron deficiency can arise without anyone expecting it. Later, once the bleeding has gone, ferritin rises again by itself.

Other questions come in. Blood lipids change unfavourably after the menopause, because the protective influence of oestrogen falls away; the risk of cardiovascular disease approaches that of men. Cholesterol, blood sugar and blood pressure therefore need checking regularly from this time on – through the general health check at your GP, which also covers liver and kidney values.

For the question of the menopause itself, however, the laboratory is less helpful than many expect. A raised FSH supports the suspicion but rules nothing out, and fluctuates considerably during the transition – a single value can be high one month and normal the next. The diagnosis follows from the symptoms and the bleeding pattern, not from a number. The menopause score sorts the symptoms by domain, because the treatment follows from that.

There is one exception: in women under 40 whose bleeding has stopped, hormone measurement is very much decisive, because premature ovarian insufficiency has to be recognised and treated – here it is about bone density and cardiovascular protection over decades.

Values frequently added in gynaecology

Thyroid (TSH). An underactive thyroid causes exhaustion, weight gain, constipation and cycle disorders, and can make pregnancy more difficult. When trying to conceive and in pregnancy, narrower thresholds apply than otherwise, because in the first trimester the baby depends entirely on the mother’s thyroid hormones.

Vitamin D. At our latitudes, too low in a large part of the population from October to March, because there is not enough sunlight for the skin to produce its own. It matters for bone metabolism, particularly in the menopause and where there are risk factors for osteoporosis.

Vitamin B12 and folate. With large red cells, with a vegetarian or vegan diet and when trying to conceive. Folic acid should be started four weeks before conception – the neural tube closes before many women know they are pregnant.

Hormone values. With cycle disorders, difficulty conceiving, suspected polycystic ovary syndrome or in the menopause. Here the point in the cycle is decisive: FSH, LH and oestradiol are measured on day three to five of the cycle, progesterone about seven days after ovulation, to check whether one took place at all. The ovulation calculator helps find the right day.

Clotting. Before prescribing oestrogen-containing contraception where the family history calls for it, and with repeated miscarriage. Screening all women before the pill, by contrast, makes no sense: it would find many harmless variants and would not identify the rare significant ones more reliably than the targeted question about thromboses in the family.

When bleeding is too heavy: what the laboratory shows

“Too heavy” is a phrase every woman uses differently – the comparison is missing, because nobody knows anyone else’s bleeding. So it helps to pin down what counts as heavy bleeding in the consulting room: when a pad or tampon is soaked through in less than two hours, when the bleeding lasts longer than seven days, when clots are passed, when you have to change at night, when the day is planned around the bleeding.

What the laboratory contributes is the objective cross-check. A low ferritin with a normal Hb shows that losses have exceeded intake for some time – even when the bleeding subjectively seems “actually normal”. Conversely, a completely normal ferritin after years of heavy bleeding suggests that absorption is keeping up.

The assessment is supplemented by TSH, because an underactive thyroid causes bleeding disorders, and where there is corresponding suspicion by clotting values: a mild, never-diagnosed clotting disorder – most often von Willebrand disease – is more common in women who have bled heavily since their first period than one would assume. If you have bled heavily since adolescence, have frequent nosebleeds and bleed noticeably after minor procedures, ask to have this looked into.

The second part of the assessment is provided by ultrasound: fibroids, polyps and adenomyosis are visible there, not in the blood. The two together give the picture – laboratory alone or ultrasound alone are not enough.

How to read a laboratory report

Three points that save a great deal of worry.

The normal range is not a boundary between healthy and ill. It is defined so that 95 per cent of healthy people fall within it – one healthy person in twenty therefore lies outside it with nothing wrong. A single slightly deviant value without symptoms is usually meaningless.

Normal ranges depend on the laboratory. Different laboratories use different methods and quote different ranges. Values from two laboratories therefore cannot simply be compared – if you want to watch a trend, stay with the same laboratory where possible.

The trend says more than the single value. A ferritin of 28 means something different if it was 80 a year ago than if it was 20 then. So bring earlier reports with you.

Where to go from here

Blood tests are part of the examination at this practice; external laboratory services are charged separately where they do not go through the insurance fund. Details are on the page Fees. If you have been feeling exhausted for some time, a blood count with ferritin and TSH is the sensible first step – make an appointment.

A word about what to expect from such tests. Not every exhaustion has a cause in the blood, and a completely normal report is not a statement that the symptoms are imagined. It rules out a group of readily treatable causes – that is a lot, but not everything. Lack of sleep, sustained strain, a depressive episode and the menopause itself cause the same symptoms and show up in no laboratory value. That is why it begins with the conversation and not with the blood test, and why a report always comes with its interpretation, not just the printout.