For a full list of tests used in diagnosis and treatment, see www.labtestonline.org.uk. The tests listed below are not comprehensive but represent those in most regular use. The normal ranges vary between laboratories so may not concur precisely with the values below.

ACETONE (urine)

Aim: Detection of diabetic ketoacidosis.

Method: Using Acetest tablets, Chemstrip or Multistix.

Normal: Negative. Positive result can be provoked by starvation and/or vomiting as well as various metabolic diseases including diabetes mellitus.

ACID PHOSPHATASE

Aim: Aid in diagnosis of prostatic cancer.

Increased concentrations of this enzyme, which is present in the kidney, semen, serum and the prostate gland, may occur in this condition.

Normal: 1–5 international units per litre.

ADRENOCORTICOTROPHIC HORMONE (ACTH) (plasma)

Aim: Diagnosis of Addison's disease, Cushing's syndrome and other disturbances of the hypothalamo-pituitary-adrenal axis.

Normal: Sleep–wake cycle of ACTH production, with highest levels at 06.00–08.00 (soon after getting up) and lowest levels at 21.00–22.00 (after going to bed). Secretion is increased by pregnancy and stress.

ALANINE AMINOTRANSFERASE (ALT)

Aim: Evaluation of liver disease

This enzyme is released from damaged liver cells so is used as one of a battery of liver function tests commonly used to test for liver disease or follow its progress.

Normal: Male adult 21–72 units/litre; female 9–52 u/l.

ALKALINE PHOSPHATASE

Aim: Evaluation of liver or bone disease.

This enzyme may be present in greater than normal amounts in several disorders including bone metastases, Paget's disease, rickets, liver disease, pulmonary infarction and heart failure.

Normal: 30–300 international units per litre.

AMNIOCENTESIS

Aim: Assessment of fetal maturity and diagnosis of fetal abnormalities.

Method/hazards: With ultrasound guidance, a needle is inserted through the mother's abdominal wall and uterus, and a specimen of amniotic fluid withdrawn. There is a small risk to the fetus and the test should only be performed when essential.

AMYLASE (serum)

Aim: Investigation of pancreatic and hepatic disease.

Normal: 25–125 U/1 (units per litre).

APGAR SCORE

Aim: Assessment of neonate's need for resuscitation.

Method: Evaluation of a newborn baby at the age of 1 minute and 5 minutes of skin colour, muscle tone, respiratory effort, heart rate, and response to stimulus. Points are calculated and resuscitation started if needed. An Apgar score still low at 10 or even 15 minutes represents a high risk for developing cerebral palsy.

ASPARTATE TRANSFERASE (AST)

Aim: Evaluation of liver disease

This enzyme is released from damaged liver cells so is used as one of a battery of liver function tests commonly used to test for liver disease or follow its progress.

Normal: Adult male: 17–59 units/litre; female 14–36 u/l.

BICARBONATE (whole arterial blood)

Aim: Investigation of acidosis and alkalosis.

An important investigation when managing patients with respiratory or renal disease or anyone whose metabolism is profoundly disturbed, for example in any intensive care situation.

Normal: 18–23 mmol/l.

BILIRUBIN

Aim: To help assess liver function (and sometimes degree of breakdown of blood cells – haemolysis)

A breakdown product of the blood pigment haemoglobin that is excreted in the bile, its concentration is raised in liver disease, obstructive jaundice, haemolytic anaemia and pulmonary infarction.

Normal: 2–17 m mol.1.

BIOPSY OF TUMOURS

Aim: Histological diagnosis of type of tumour and malignancy.

Methods: Fine-needle and large-needle aspiration biopsy – excision biopsy.

BLOOD GASES

Aim: To assess the adequacy of respiration by measuring dissolved gases in blood (preferably arterial).

Methods: Sample of blood taken into heparinised syringe (to prevent clotting) and gases analysed. Gold standard is an arterial sample but, when impracticable, a capillary sample from a warm extremity is an alternative. pH is the reciprocal of the concentration of hydrogen ion, so a measure of acidity, pCO₂ and pO₂ carbon dioxide and oxygen respectively.

Normal: pH 7.36–7.44; pCO₂ 4.5–6 kilopascals; pO₂ 10–14 kPA.

B-TYPE NATRIURETIC PEPTIDE

Aim: To evaluate the presence and severity of heart failure.

This enzyme is released soon after damage has occurred to heart muscle cells.

Normal: Very dependent on age and sex but normally less than 200 picograms/ml.

BRCA-1

Aim: To determine whether a patient carries a gene responsible for breast cancer.

If a woman has a strong family history of breast cancer or if a family member is known to carry the gene, then the test can be performed to assess risk.

Normal: Absent. If present then prophylactic treatment may be advised, such as mastectomy.

CALCIUM (serum)

Aim: Diagnosis of hyperparathyroidism, hypoparathyroidism, etc.

Normal: 2.2–2.6 mmol/L but varies with level of blood protein. Range may be affected by other drugs.

CARDIAC STRESS TEST

Aim: Assessment of cardiac efficiency.

Method: Heart rate, blood pressure, and electrocardiograph are recorded continuously while the patient performs an incremental work test. The test is stopped whenever requested, e.g. in the presence of excessive breathlessness, chest pain.

Contraindications include acute infection, recent myocardial infarction, unstable angina, congestive heart failure, uncontrolled dysrhythmia, etc.

CERVICAL CANCER SCREENING

Aim: Early detection of changes in cervical cells, allowing earlier treatment.

Method: Starting 6 months after first intercourse, then at 3-yearly intervals for rest of life. The test involves a cervical smear with a spatula, the cells then being examined histologically.

CHOLECYSTOGRAM

An X-ray of the gall-bladder after the patient has taken a contrast medium by mouth; it is concentrated in the gall-bladder, thus enabling identification of abnormalities such as gall- stones, tumours and restricted patency of the cystic duct (which carries the bile from the gall-bladder to the duodenum).

CHOLESTEROL

Aim: A fatty substance present in several forms in tissues and blood where its concentration ranges from 3.6–7.8 mmol/l. Raised concentrations (hypercholesterolaemia) are often associated with atheroma, which can cause cardiovascular or cerebral vascular disease, and are linked with a high intake of saturated fats and cholesterol, though damage to blood vessels may be caused by one form of cholesterol called low-density lipoprotein (LDL) at a concentration above 4.4 mmol/l.

CHORIONIC GONADOTROPHIN (urine, first morning specimen)

Aim: Diagnosis of pregnancy.

Methods: Agglutination inhibition assay: positive in pregnancy 8–14 days after first missed period. Monoclonal antibody test: positive in pregnancy 14–18 days from conception.

CHORIONIC VILLUS SAMPLING

Aim: Ascertainment of fetal chromosome pattern.

Method: A small sample of trophoblastic tissue is obtained from the placenta, by ultrasound guidance either transvaginally or transabdominally, taken between the 9th and 11th weeks of pregnancy. There is a small risk of abortion.

CORDOCENTESIS

Aim: Investigation of the chromosome pattern and haemoglobinopathies in mid-pregnancy.

Method: Blood is withdrawn from the umbilical cord at about the 18th week of pregnancy and extensively analysed.

CREATINE KINASE

Aim: To aid in diagnosis and management of muscle disease.

This enzyme is released into the blood by damaged muscle cells.

Normal: Adult male 55–175 units/litre; female 30–135 u/l.

C-REACTIVE PROTEIN

Aim: to assess likelihood and to monitor the presence of inflammation.

This is a protein produced by the immune system in response to an antigenic stimulus so can be used to aid in determining whether the patient is likely to have an infection or an autoimmune disease and to monitor their progress over time.

Normal: Less than 5 units.

ENZYME-LINKED IMMUNOSORBENT ASSAY (ELISA) (urine)

Aim: Diagnosis of presence of antibodies, for example to bacteria and viruses.

ERYTHROCYTE COUNT (whole blood)

Aim: Investigation of anaemia.

Normal: 4.2–6.1 × 10⁶ red cells per microlitre of blood, depending on age and sex.

ERYTHROCYTE SEDIMENTATION RATE (ESR)

Aim: Investigation and monitoring of fever, inflammatory, malignant, or autoimmune disease.

Method: Anticoagulated whole blood is used. The result obtained may be influenced by numerous factors, notably various disorders and different drugs. It has been largely replaced by C-reactive protein.

Normal:

GLASGOW COMA SCALE (MODIFIED)

Aim: To test the depth of coma, particularly following head injury, as a guide to the need for neurosurgical intervention.

Method: Opening of the eyes, best verbal response, and best motor response are scored separately, giving a total quantitative index of the level of cerebral dysfunction.

GLOMERULAR FILTRATION RATE (GFR)

Aim: Investigation of renal function.

Method: Plasma and urinary creatinine levels are measured and the creatinine clearance rate calculated. This corresponds closely to the GFR, normally 120 ml/min in adults.

GLUCOSE (blood, urine)

Aim: Diagnosis and monitoring of diabetes mellitus.

Method: Stick tests available for urine and blood samples.

Normal: See tables B1 and B4 (pages 804, 805).

GLUCOSE TOLERANCE TEST (ORAL)

Aim: Diagnosis of diabetes mellitus/impaired glucose tolerance.

Method: Pre-test patient, ensure no recent illness, accident, or surgery. Discontinue non-essential drugs. Patient fasts for 10–16 hours, then takes 75 g glucose over 5 minutes. Serum glucose level is measured at 0, 30, 60, 90 and 120 minutes. The test should be performed in the morning.

Normal:

GLYCATED HAEMOGLOBIN (Haemoglobin A_1C)

Aim: Monitoring of diabetes mellitus.

Method: The test reflects the mean blood-glucose concentration over the previous 4–8 weeks. It is a measure of long-term control and should be repeated at around 3-monthly intervals.

Normal: (In insulin-dependent diabetic) 2.0–4.2. Diabetic in good control 4.8–5.9.

HAEMATOCRIT (PACKED RED CELL VOLUME) (whole blood)

Aim: Investigation of anaemia and polycythaemia.

Normal: adult male 38.8–50%; female 35–44%.

FULL BLOOD COUNT

Aim: To assess the presence and extent of anaemia, bone marrow function, likely infection and one element of blood clotting potential.

The elements of blood tested include total haemoglobin, packed cell volume, mean corpuscular haemoglobin concentration and volume, granulocyte, lymphocyte and platelet counts.

Normal: Haemoglobin – adult male 13.5–17 grams/decilitre; female 12–15.5; white cells 3.5–10.5 (x10⁹/litre); platelets 150,000–450,000[

HEPATITIS A ANTIGEN (serum)

Aim: Diagnosis of hepatitis A infection.

Normal: Negative.

Anti-HAV IgG appears about four weeks after infection and persists indefinitely.

HEPATITIS B SURFACE ANTIGEN (serum)

Aim: Diagnosis of active or chronic hepatitis B virus infection.

Normal: Negative.

HUMAN IMMUNODEFICIENCY VIRUS (HIV) ANTIBODY (serum)

Aim: Diagnosis of HIV infection.

Method: HIV antibodies are usually detectable from 4 weeks to 4 months after infection, and persist indefinitely. The test is by enzyme-linked immunosorbent assay (ELISA).

Normal: Negative.

IRON (serum)

Aim: Investigation of anaemia.

Normal: 10.75–30 micromoles/litre.

LIVER FUNCTION TESTS

The liver is a complex organ with metabolic, excretory and protective functions that are interdependent, so there is no single test to assess overall function. Liver biopsy, done under local anaesthetic with entry through the skin, gives helpful diagnostic information with little risk or discomfort to the patient. The procedure enables liver tissue to be examined in the laboratory for structural changes and the presence of abnormal cells.

Several tests of blood chemistry detect changes in the various functions, as well as assessing the healthiness of liver cells. These include tests on blood serum for the amounts of bilirubin (yellow breakdown products of red blood cells), albumin (a key body protein made in the liver) and alkaline phosphatase (an enzyme in bile) and aminotransferases or transaminases (enzymes entering the blood following liver-cell damage). Prothrombin time (see below) tests how well the blood clots: the process depends on the presence in the blood of vitamin K (see APPENDIX 5: VITAMINS) which is produced by the normal liver; damage to liver cells lengthens the time blood takes to clot. X-ray and ultrasound assessment of liver and gall-bladder structure are valuable, as are radionuclide scanning and computed tomography.

LUMBAR PUNCTURE

Aim: To obtain samples of cerebrospinal fluid (CSF) for investigation of central nervous system diseases, especially meningitis.

Method: With the patient lying on his or her side, and under local anaesthesia, a long needle is inserted between the third and fourth lumbar vertebrae. When performed correctly, a small volume of fluid should flow out spontaneously; this is collected and analysed for the presence of blood cells, bacteria and the levels of protein and sugar.

The test should never be carried out in the presence of a raised CSF pressure, since it may precipitate transtentorial or tonsillar herniation in the brain.

OCCULT BLOOD

Aim: Detection of the presence of blood not obviously visible to the naked eye.

Method: A tiny piece of faeces is brought into contact with a chemical which changes colour in the presence of even very small quantity of blood.

Normal: Absent. If present suggests possibility of gastrointestinal bleeding such as from inflammatory bowel disease, a polyp or carcinoma. It is the basis of a screening test in those aged over 65, with positive results leading to the need for further investigation.

POTASSIUM

Aim: To test for raised or lowered concentrations of this essential element present as an electrolyte in the blood. Abnormally low or high levels are found in a wide range of disorders. Low: cirrhosis of liver, malnutrition, vomiting, diarrhoea, diuresis, hyperadrenalism. High: diabetic acidosis, hypoadrenalism, haemolysis, renal tubular defect, thrombocytosis.

Normal: 3.5–5.0 m mol/l.

PROSTATE SPECIFIC ANTIGEN (PSA)

Raised concentration is present in the presence of prostate cancer. The test can be used as part of diagnostic testing but is particularly useful in follow-up of patients treated for the disorder as it may provide evidence of recurrence. In some countries it is performed as a screening test but the evidence suggests it functions poorly because of the high risk of false positives which may provoke unnecessary treatment.

Normal: 0–4 ng/ml.

Ultrasound scanning and biopsy of the gland are essential diagnostic tests.

PROTHROMBIN TIME

Aim: To test quantitatively the amount of prothrombin in the blood based on the time it takes blood plasma to clot in the presence of thromboplastin and calcium chloride. It measures the integrity of the blood-clotting function.

Normal: 10–14 seconds.

The time is extended in haemophilia, serious liver disorders and when the diet is deficient in vitamin K.

SKIN BIOPSY

Aim: Histological or immunofluorescent examination of skin lesions, especially if there is any suspicion of malignancy.

Method: Various techniques are used, depending on the amount of skin required and the degree of doubt of the diagnosis.

SODIUM

Aim: To test for raised or lowered concentrations of this essential element present as an electrolyte (sodium chloride) in the blood. Abnormally low or high levels are found in several disorders. Low: nephrosis, myxoedema, heart failure, diarrhoea and vomiting, diabetic acidosis, diuresis, adrenocortical insufficiency, excessive intravenous fluid administration. High: dehydration, diabetes insipidus, excessive salt intake, diabetes mellitus.

Normal: 135–145 mmol/l.

THYROXINE, FREE (FT4) (serum)

Aim: Measurement of thyroid function.

Method: Various methods are used. The normal value is 10–31 pmol/l, but varies with the technique used.

TROPONIN

Aim: Diagnosis of myocardial infarction.

A raised level of this enzyme or a changing level between two tests is part of the definition of myocardial infarction, especially useful if the ECG does not provide confirmatory evidence. False positives can occur, for example after strenuous exercise such as marathon running.

Normal: Less than 14 nanograms/litre. If raised on first sample, diagnosis confirmed. If normal but rises by 20–100% over next 9 hours, then myocardial infarction possible and further investigation needed. If rise above 100% then diagnosis confirmed.

TUBERCULIN SKIN TESTS

Aim: Diagnosis of tuberculosis.

Method: Antigens of Mycobacterium tuberculosis are injected intradermally. A positive result means that the patient has encountered the tubercle bacillus at some time in their life but not necessarily that they are currently infected.

UREA

Aim: Assessment of kidney function.

If the kidney function is inadequate, not all urea – a breakdown product of proteins – is excreted so the blood level rises. It may be raised also in dehydration.

Normal: 2.5–7.5 mg/dl.