The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [417]
Hyponatraemia (serum sodium <135 mmol/L) may be indicated in fluid retention (oedema)
Potassium 3.5–5.2 mmol/L Potassium plays a major role in nerve conduction, muscle function, acid/base balance and osmotic pressure. It has a direct effect on cardiac muscle, influencing cardiac output by helping to control the rate and force of each contraction
The most common cause of hyperkalaemia (serum potassium >5.2 mmol/L) is chronic renal failure. The kidneys are unable to excrete potassium. The level may be elevated due to an increased intake of potassium supplements during treatment. Tissue cell destruction caused by trauma/cytotoxic therapy may cause a release of potassium from the cells and an elevation in the potassium plasma level. It may also be observed in untreated diabetic ketoacidosis
Urgent treatment is required as hyperkalaemia may lead to changes in cardiac muscle contraction and cause subsequent cardiac arrest
The main cause of hypokalaemia (serum potassium <3.5 mmol/L) is the loss of potassium via the kidneys during treatment with thiazide diuretics. Excessive/chronic diarrhoea may also cause a decreased potassium level
Urea 2.5–6.5 mmol/L Urea is a waste product of metabolism that is transported to the kidneys and excreted as urine. Elevated levels of urea may indicate poor kidney function
Creatinine 55–105 µmol/L Creatinine is a waste product of metabolism that is transported to the kidneys and excreted as urine. Elevated levels of creatinine may indicate poor kidney function
Calcium 2.20–2.60 mmol/L Most of the calcium in the body is stored in the bone, but ionized calcium, which circulates in the blood plasma, plays an important role in the transmission of nerve impulses and the functioning of cardiac and skeletal muscle. It is also vital for blood coagulation
High calcium levels (hypercalcaemia >2.6 mmol/L) can be due to hyperthyroidism, hyperparathyroidism or malignancy. Elevation in calcium levels may cause cardiac arrhythmia, potentially leading to cardiac arrest (Blann 2007)
Tumour cells can cause excessive production of a protein called parathormone-related polypeptide (PTHrp) which causes a loss of calcium from the bone and an increase in the blood calcium levels. This is a major reason for hypercalcaemia in cancer patients (Higgins 2007)
Hypocalcaemia (<2.20 mmol/L) is often associated with vitamin D deficiency due to inadequate intake or increased loss due to GI disease. Mild hypocalcaemia may be symptomless but severe hypocalcaemia may cause increased neuromuscular excitability and cardiac arrhythmias. It is also a common feature of chronic renal failure (Higgins 2007)
C-reactive protein (CRP) <10 mg/L Elevation in the CRP level can be a useful indication of bacterial infection. CRP is monitored after surgery and for patients who have a high risk of infection. The CRP level can help monitor the severity of inflammation and assist in the diagnosis of conditions such as systemic lupus erythematosus (SLE), ulcerative colitis and Crohn’s disease (Higgins 2007)
Albumin 35–50 g/L Albumin is a protein found in blood plasma which assists in the transport of water-soluble substances and the maintenance of blood plasma volume
Bilirubin (total) <17 µmol/L Bilirubin is produced from the breakdown of haemoglobin; it is transported to the liver for excretion in bile. Elevated levels of bilirubin may cause jaundice
Liver function tests
There are numerous tests which are used to assess liver function. Additional tests include alkaline phosphatase, gamma-glutamyl transferase (GGT), aspartate aminotransferase (AST) and alanine aminotransferase (ALT).
Microbiology
Various types of sample may be sent to the microbiology laboratory for screening, for example blood, urine, faeces and sputum. Blood tests sent to microbiology may include screening for hepatitis B, hepatitis C and HIV.
Blood cultures
Definition
A blood culture is a