Common Tests. Creatinine Clearance

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1 Common Tests Although doctors use tests to help aid their diagnoses, these are not comprehensive; there are always exceptions. If you would like further information please Dr Wilson or discuss with your GP. Creatinine Clearance The creatinine clearance is usually reported along with the creatinine. It often better reflects kidney function, it is graded into 5 levels 1-5 with 1 being normal and 5 very poor. Patients in groups 4 and 5 (<30ml/min) should probably be under the care of the hospital renal clinic, if not already under the clinic they should mostly be referred urgently. Patients in groups 3 and 4 creatinine clearance between 30ml/min and 90ml/min should be monitored routinely every 6 (30ml-59ml/min) to 12 (60ml-90ml/min) months. In patients with GFR > 60ml/min if there is no other evidence of kidney disease (persistent microalbuminuria, proteinuria, haematuria, structural abnormalities or glomerulonephritis) then routine follow up is not necessary. Patients in groups 3 and 4 should have blood pressure, haemoglobin, urine for protein/microalumin/blood checked routinely. Ask a doctor if you have any uncertainty as it is a complex area. Gamma GT A very sensitive liver enzyme that is commonly raised. It is induced by many substances, if raised and the other liver tests are normal then this may be due to regular medication the patient is taking. It varies with age being highest between 30 and 50 years old and is higher in men than in women. It is usually raised in heavy alcohol drinkers. It is raised in most liver diseases, along with the other liver function tests, and also in pregnancy. Glucose The blood sugar or glucose level is controlled in a narrow range in most people. Diabetic patients have a lack of effective insulin the hormone that moves sugar from the blood into the cells, thus their sugar levels rise unless they take medication to keep it down. If diabetic patients take excess medication especially insulin or the biguanide tablets like gliclazide then the sugar level can go too low ( hypo ) and the patient can even lose consciousness (call 999). People who are not on these medications do not lose consciousness from a low sugar level and feelings of low blood sugar and needing sugary food are rarely significant of disease. The WHO definition of diabetes is two fasting (no food for 12 hours) sugar levels above 7.0mmol/l. If patients have eaten the level can rise to 11.0 or so in the following few hours. Diabetic patients will often have a sugar level that is higher than normal despite treatment as it is difficult to keep it in the normal range. If the level goes above they are at risk of needing hospital treatment. Haemoglobin The concentration of the oxygen carrying molecule in the blood. The normal ranges vary according to age and sex but are approximately 13.5 to 17.5 in men, 12 to 15.5 in women. The level can be increased by concentration of the blood for example in dehydration or due to excess production of red cells as in polycythaemia. When decreased people are said to be anaemic there are usually few symptoms from mild anaemia but the important thing is to consider why the person is anaemic.

2 Anaemia can occur suddenly from severe bleeding when people usually attend casualty, or gradually from for example slow blood loss, as from heavy periods or invisibly from for example a stomach ulcer. The haemoglobin can also fall due to reduced production as in low vitamin B12 or folic acid states. If the anaemia is due to iron loss the red cells will tend to be small (low mcv), low mcv however is also due to inherited carrier states such as thallasaemia trait (detected by a further test haemoglobin electrophoresis) which has no need of any treatment, though carriers should be aware of whether their partner is also a carrier as if so any children they may have may get the full disease. If anaemia is from low B12 or folate the mcv tends to be raised. Further uncommon causes of anaemia are due to increased breakdown of the red cells (haemolytic anaemia) or reduced production due to failures in the bone marrow. HbA1c The glycosylated haemoglobin is mainly used to monitor diabetes. Some of the blood sugar is always attaching to the haemoglobin and as red blood cells only live for 3-4 months this test gives a reading that indicates the average sugar level from the past 3 months. It should ideally be under 7.0 but few diabetics manage such a good level long term. If the level is rising it is worth considering increasing medication to try and reduce long term complications. Lipids Fasting Lipids: This test is composed of cholesterol (broken into the HDL and LDL forms) and triglcerides. Cholesterol (levels are in mmol/l; to convert to mg/dl multiply by 38.67) There are two rules depending on whether it is primary or secondary prevention. Secondary prevention is for people who have already had an illness related to narrowing of the blood vessels, for example angina or diabetes. Primary prevention is for people who have never had such an illness. As lipid levels are a risk factor for narrow arteries and therefore people with such an illness presumably already have a degree of blood vessel narrowing the targets for lipids in secondary prevention are lower. Other factors related to narrowing of the blood vessels such as blood pressure, smoking, blood sugar levels etc should also be looked at in secondary prevention. 1 Secondary Prevention: People who have already had a vascular disease* should aim to keep their total cholesterol less than 5.0. There is some disagreement as to how low is best, some people advocate keeping total cholesterol less than 4.0 but others are not sure there may be some not yet proven problem with aiming for too low a level. Another target in secondary prevention is to keep the LDL (or bad ) cholesterol les than Primary Prevention: People who have never had an arterial disease are presumed to be at lower risk. The guidance in the main currently uses the total cholesterol to HDL ( good ) cholesterol ratio as the critical measurement, HDL cholesterol is known to protect against vascular disease. There are tables merging several of the risk factors (smoking, diabetes, blood pressure, age) together giving a % risk of vascular disease over the next 10 years. Currently a risk of 20% or more is used as the threshold for beginning cholesterol lowering treatment. If the total cholesterol to HDL ratio is over 5.0 we advise a repeat level after 6 months during which the patient should try to lose some weight, and eat a low fat diet. If the level is still above 5.0 on repeat we would advise making a routine appointment with the doctor to have the other risk factors documented and the 10 year % risk

3 calculated before making a decision about treatment. In people with a family history of heart disease for example it is thought increasing the % risk score by a further 50% is reasonable. If total cholesterol > 8.0 however it is possible the patient has a familial tendency to high cholesterol and will probably require treatment you should see a doctor anyway at this level. *Vascular/arterial disease list Ischaemic heart disease : angina, myocardial infarction ( heart attack, coronary ) diabetes, peripheral arterial disease (claudication). Some people would add left ventricular failure, renal failure. Mean Corpuscular Volume Known as the mcv this is a measure of the size of the red blood cells. It is low in iron deficiency and in thallasaemia carrier states. It can be reduced in other illnesses, and it is not always reduced in iron deficiency. It can be raised in vitamin B12 and folic acid deficiency states, in liver disease, in alcohol dependency, underactive thyroid amongst others. Anyone with an abnormal mcv should have further tests to look for these possible underlying illnesses unless they are already known to be thallasaemia carriers and the haemoglobin is stable. Platelets Platelets are small cell fragments partially responsible for clotting of blood. They can be increased in some inflammatory and bone marrow conditions and decreased due to certain medications, enlargement of the spleen, alcohol dependence. If they fall very low bleeding can occur, if they rise clotting is more likely. Potassium Potassium levels are normally kept within a tight range in the blood, mmol/l. Levels below 3.0 and above 6.0 are potentially serious and require urgent confirmation. Generally potassium levels rise when people are dehydrated and fall if there is inadequate intake or vomiting or diarrhoea. Potassium is stored within cells and the commonest reason for a raised potassium is leakage out of the cells due to the blood not being analysed quickly. Delayed analysis often occurs because of slow transport to the hospital. Potassium sparing diuretics like amiloride, spironolactone, the ACE inhibitors (usually ending in pril as in ramipril) and the sartans (as in losartan) are a fairly common cause of raised potassium due to their actions on the kidney. Reduced kidney function tends to cause rises in potassium. There are many other rare causes. Sodium Sodium levels are normally kept within a tight range in the blood, mmol/l. Levels below 125 and above 155 are potentially serious and require urgent confirmation. Generally sodium levels rise when people are dehydrated and fall if there is excess water intake. Vomiting and diarrhoea can cause either abnormality. Diuretics are a fairly common cause of low sodium due to their actions on the kidney. There are many other rare causes. Triglycerides Triglycerides are another blood lipid but raised levels have not been thought to be so important as cholesterol. A level above 2.0 mmol/l may be associated with an increased risk of coronary heart

4 disease. If your level is above 2.0 mmol/l we would advise repeating it in 6 months during which time you should try and eat a low fat diet. Alcohol can raise triglyceride levels so it would be sensible to reduce this too. Triglycerides are also often raised if you are overweight or have diabetes. Raised levels can also lead to pancreatitis sometimes. Urea Urea along with creatinine measures kidney function. It is raised if there is a reduction in kidney function, it can be reduced in malnutrition, cirrhosis. White Cell Count The various white cells are involved in infection and allergy. The main subsets are the neutrophils and the lymphocytes, the former tend to rise in bacterial infections the latter in viral infections. White cell counts can occasionally be reduced or increased due to bone marrow problems. White cell counts tend to rise somewhat in people on long term steroids. Very high levels can occasionally be a sign of leukaemia. Alkaline Phosphatase Alkaline Phosphatase is an enzyme that if raised suggests liver or bone problems. If the problem is with the liver then the gamma GT test is usually also raised whereas it remains normal in bone disease. Liver abnormalities causing obstruction to the flow of bile particularly affect this enzyme, so the test is raised more than ALT (the other main liver enzyme tested) when gall stones or other diseases block the bile duct. If the enzyme is bone in origin the likeliest diseases are Paget s disease of bone, osteomalacia, some other diseases of bone. It is also raised in the later stages of normal pregnancy. ALT ALT is an enzyme in liver cells, it leaks out into the blood when they are being damaged. It is therefore a test of active liver cell damage. Very high readings usually mean acute hepatitis. Mild raised levels are quite common, often resolve spontaneously but if persistent may be due to many causes such as fatty liver, chronic hepatitis, alcohol, heart failure, muscle damage. Bilirubin Bilirubin is a product of the breakdown of haemoglobin in blood cells that is occurring naturally all the time. If it is raised much above 30micromol/l people become visibly jaundiced. Raised on its own when the other main liver tests (ALT, Alkaline Phosphatase) are normal usually means a harmless inherited deficiency of an enzyme as in Gilbert s syndrome, the rise will be fairly mild and worse when the patient is starved. If the other liver enzymes are raised jaundice suggests a liver disease such as gall stones or other diseases obstructing the bile duct, liver cell damage e.g. viral or alcoholic hepatitis, cirrhosis, and some haemolytic blood disorders involving excess red cell breakdown. Chloride and Bicarbonate These negative ions in the blood rarely move out of their normal ranges in general practice. They can become low or high in patients with fluid loss such as from severe diarrhoea and vomiting, severe

5 respiratory problems, due to certain medications and in kidney failure and others. Any abnormality should be discussed with the doctor. Creatinine Creatinine levels are used to monitor kidney function and tend to slowly rise with age. They can be reduced in people with low muscle mass. Elderly patients commonly have a slightly raised level, as do some people on diuretics; a raised level should be discussed with the doctor unless it is stable, already known and longstanding.