Blood tests

This fish is suffering from massive haematemesis which, one the one hand, is very bad news, but on the other hand, makes it very easy to do a blood test.

There are a lot of blood tests. Like, billions. We are going to tell you about the key ones.

Full Blood Count (FBC)

This is common to do. It's pretty much your standard. Especially important to do in infection, heart problems, surgery and anaemia.

• White blood cell (WBC) tells you about of white blood cells per volume of blood. Normal is around 4-11x10⁹/L. Low means immunosuppression, high means infection or cancer.

White blood cell differential looks at the types of white blood cells present:

• • Neutrophils (40-75%) (raised in bacterial infection)
  • Lymphocytes (20-45%) (raised in viral or bacterial infection, and in haematological cancer)
  • Monocytes
  • Eosinophils
  • Basophils
• Haemoglobin is the amount of Hb in the blood. Normal is around 13-18g/dL in men and 11.5-16g/dL in women. High means dehydration, cancer or lung disease. Low is anaemia: check the page for causes.
• Platelet count is the number of platelets. Normal is around 150-400x10⁹/L. Low points to cancer, chemo or autoimmune problems, whilst high signifies haematological cancer.
• Mean corpuscular volume (MCV) is average size of your red cells. Its raised in some anaemia, and lowered in others. Visit the Causes of anaemia page for more on types.

Clotting (CLS)

There are a variety of tests they do, such a Prothrombin Time (PT) and Partial Thromboplastin Time (PTT). They are generally used to test people before surgery, to test the effectiveness of anticoagulation or to isolate weird bleeding disorders, such as Haemophilia and von Willibrand's disease.

Urea and Electrolytes (U+Es)

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.
• Calcium (Ca²⁺)
  • 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.

Liver Function Tests (LFTs)

• Albumin (ALB) - it's the main protein in blood, produced by the liver. Low albumin is seen in nephrotic syndrome(where is leaked out) and liver failure (where it's not produced).
• Alanine Transaminase (ALT) - An enzyme found in liver cells. When liver cells are damaged, they leak this out, so its a marker of liver damage.
• Aspartate Transaminase (AST) - Similar to ALT, but less specific to the liver - can go up in heart damage too.
  • The main use for AST is that when AST and ALT are both raised, and ALT is higher, it points to viral hepatitis. When AST is higher, it points to alcoholic hepatitis. I remember this as LOVE SAKE:
    • So you can get viral hepatitis from making love and ALTs go up.
    • Sake is a type of wine, and drinking too much gives you alcoholic hepatitis, and your ASTs go up.
• Alkaline Phosphatase (ALP) - is an enzyme found in the ducts of the biliary tree. Thus when there is damage or obstruction in the bile ducts, more of it gets released and goes into the blood. Also goes up in Paget's disease of bone, due to increased bone turnover.
• Gamma glutamyl transpeptidase (GGT) - mostly used because it is raised in chronic alcohol abuse.
• Total bilirubin (TBIL) - amount of bilirubin in the blood.
• Direct bilirubin (Conjugated BR) - amount of conjugated bilirubin, enabling you to work out what type of jaundice is going on.

Inflammatory markers (ESR and CRP)

Essentially, these are used in a variety of different tests to confirm and inflammatory process has taken place. This can occur in infection but frankly, anything that makes you signficantly ill, or causes any inflammatory response can cause a rise in both of these tests.

CRP is more acute, whereas ESR remains high for weeks after an event. So CRP is more useful as a guide to what kind of effect treatment is having. Since both are not very specific, they are rarely used on their own, but in combination with other measures.