Generally used to assess the workings of the kidney, and to check that electrolytes are in balance, and the patient isn’t gonna drop dead.
Sodium (Na+): 135-145 mmol/L
low is hyponatraemia: from sodium loss (d&v, thiazide diuretics, excessive sweating, kidney disease or Addison’s), from excess fluids (drinking too much water, heart failure, cirrhosis, nephrotic syndrome). Sometimes your body makes too much ADH, leading to extra water and thus low sodium.
high is hypernatraemia: almost always due to dehydration. Rarely, due to increased salt intake, Cushing’s syndrome, or diabetes insipidus.
Potassium (K+): 3.7-5.2mEq/L
low is hypokalaemia: from potassium loss (diarrhoea and vomiting, from insulin use, or from use of non potassium sparing diuretics.
high is hyperkalaemia: caused by kidney disease, Addison’s, injury to tissue, infection, diabetes and too much IV potassium. Also caused by some types of drugs, NSAIDS, beta blockers, ACE inhibitors and potassium sparing diuretics.
Creatinine – High creatinine implies the kidneys are having issues. Main causes glomerulonephritis, pyelonepritis, acute renal failure, deydration and shock. Rarely low, and not usually an issue if it is.
Urea – normal 2.5 – 7.9 mmol/L – goes high for the same reasons as creatinine.
low is hypocalcaemia: underactive parathyroid, low Vitamin D, CKD, alcoholism.
high is hypercalcaemia: two big causes: hyperparathyroidism and cancer (bony mets release calcium). Other causes are hyperthyroidism, sarcoidosis, TB and kidney transplant.
Albumin – low implies liver disease, or kidney problems, inflammation, shock. High usually implies dehydration.
How the Test is Performed
The U&E test is a blood test and requires a few millilitres of blood from a vein. In newborn babies blood may be taken from a heel-prick sample.
Medical Conditions and Symptoms
U&E is usually performed to confirm normal kidney function (renal function) or to exclude a serious imbalance of biochemical salts in the bloodstream. A diverse number of conditions may be detected on the U&E test, as each parameter tested may be high or low. These conditions include:
hyponatraemia (low sodium)
hypernatraemia (high sodium)
hypokalaemia (low potassium)
hyperkalaemia (high potassium)
metabolic acidosis (low bicarbonate)
metabolic alkalosis (high bicarbonate)
dehydration (high urea and/or creatinine)
renal (kidney) impairment or failure (high urea and/or creatinine)
gastrointestinal bleeding (high urea)
hypoglycaemia (low glucose)
hyperglycaemia (high glucose)
Each of these conditions in turn have several possible causes.