Blood Tests Flashcards
List some causes of high Hb.
- Dehydration
- Diuretic therapy
- Secondary to anoxia (high altitude, hypoxic respiratory conditions, heavy cigarette smoking)
- Secondary cause e.g. polycythaemia rubra vera
Name a cause of low and high Hct.
Low in any anaemia and high in polycythaemia.
What does MCV stand for? What is MCH?
Mean corpuscular volume - average volume of patient’s RBCs. Helps to morphologically classify anaemia, dependent on its cause. Low = microcytic, normal = normocytic, high = macrocytic
Mean corpuscular haemoglobin - average haemoglobin content in an RBC. If low typically shows hypochromia. Can be seen in iron-deficiency and haemoglobinopathies.
What diagnosis does MCHC aid with?
Mean corpuscular haemoglobin concentration (MCHC) – average haemoglobin concentration per RBC. Helps to classify microcytic anaemias. Low levels are typical of iron deficiency or thalassaemia; very high often reflect spherocytosis or RBC agglutination.
What does high RDW suggest?
Red cell distribution width (RDW) – a measure of the variation in RBC size.
If high this suggests a large variation in sizes, seen in iron deficiency, myelodysplastic syndrome and haemoglobinopathies.
List some causes of thrombocytosis.
Reactive:
- Blood loss
- Infection
- Inflammation
- Post-splenectomy
Autonomous:
- Genetic abnormalities
- Malignancies
List some causes of thrombocytopenia.
- Drugs
- Foods
- Infections
- Liver disease e.g. hypersplenism
- Alcohol
- Nutrient deficiency
- Pregnancy
- Bone marrow disorder
- Inherited
- Bleeding - platelets initiate mechanisms that repair injury to thr vascular endothelium. Can be high (thrombocytosis) or low (thrompocytopenia)
What type of infections are these cells most commonly associated with?
- Neutrophils
- Lymphocytes
- Monocytes
- Eosinophils
- Basophils
- Neutrophils - bacterial
- Lymphocytes - viral
- Monocytes - chronic infection
- Eosinophils - allergies/parasites
- Basophils - viral/urticaria
List 3 causes of neutrophilia and neutropenia.
Neutrophilia
- bacterial infection
- steroids
- post-surgery
- burns
- vasculitis
- neoplasia
Neutropenia
- infection
- drugs (chemo)
- autoimmune e.g.CTD, hereditary
List 3 causes of lymphocytosis and lymphopenia.
Lymphocytosis
- reactive (viral infection, stress)
- metabolic syndrome
- primary (malignancies)
Lymphopenia
- steroids
- immunosuppressive agents
- AI disease
List 3 causes of monocytosis.
- Chronic infection (TB, syphilis)
- IBD
- carcinomas
- myelodysplastic syndromes
List 3 causes of eosinophilia.
- allergy
- neoplastic
- CTD
- parasitic infection
List 3 causes of basophilia.
- Viral infection
- Urticaria
- Hypothyroidism
- Post-splenectomy
- UC
What information is found through requesting U&Es?
Sodium, potassium, chloride, urea, creatinine
Common to also get eGFT reported
What are the normal ranges for sodium?
135-145
Hyponatraemia:
- Na < 135; Mild:
- 130-134, Moderate:
- 120 -129, Severe <120
Hypernatraemia:
- Na >145
Is sodium an intra/extracellular ion? How is its concentration maintined?
Extracellular
It is closely linked to fluid as water follows solutes by osmosis. Sodium reabsorption is increased by aldosterone in the DCT. ADH causes reabsorption of water (alone) from the collecting duct.
How can you divide the causes of hyponatraemia? Why can it be fatal?
Into hypovolaemia, euvolaemia, hypervolaemia.
It can develop rapidly and water can shift into the brain causing cerebral oedema.
Summarise the 2 causes of hyponatraemia in hypo/eu/hypervolaemia.
Hypovolaemia = Na lost and H2O follows
Na loss from kidneys:
- -Addison’s Disease
- -Diuretics
- -Kidney Injury
- -Osmotic diuresis
Na loss from elsewhere:
- -Diarrhoea and vomiting
- -Burns
- -Fistula
Euvolaemia = Normal Na quantity, H2O gained
- SIADH
- Hypothyroidism
- Glucocorticoid insufficiency
- Water intoxication
Hypervolaemia = Excess ADH released secondary to intravascular fluid depletion (due to extravasation)
- CCF
- Hypoalbuminaemia e.g. cirrhosis, nephrotic syndrome
List two causes of hypernatraemia in hypo/euvolaemia.
Hypovolaemia
- Fluid loss
- Burns
- Diarrhoea and vomiting
- Diabetes insipidus
- Osmotic diuresis
Euvolaemia
- Iatrogenic
- Excess IV crystalloid
- Sodium containing drugs
What are the normal ranges of potassium? Is it mostly intra/extracellular?
What increases potassium uptake and excretion?
3.5- 5.0 (4.2 is normal) - levels outside this can have cardiac effects.
90% intracellular ion
- Uptake - insulin and catecholamines
- Excretion - aldosterone
List 2 causes of hypokalaemia caused by:
- increased renal excretion
- increased cellular uptake
- other loss
Increased renal excretion
- Thiazide or loop diuretics
- Endocrine - steroids, Cushing’s, Conns
- RTA - hypomagnasaemia
Increased cellular uptake
- Salbutamol
- Insulin
- Alkalosis
Other loss:
- Intestinal fluid loss
- Burns
- Malnutrition
What are the ranges for mild moderate and severe hyperkalaemia? What causes pseudohyperkalaemia?
K>5.5;
- Mild: 5.5-5.9,
- Moderate: 6.0-6.4,
- Severe: >6.5 mmol/L.
Note can also be pseudohyperkalaemia due to haemolysis.
What are the causes of hyperkalaemia caused by
- Reduced renal excretion
- Increased cellular release
- Excess load
Reduced renal excretion
- Acute/chronic kidney injury
- Drugs (K sparing diuretics, ACEi, NSAIDs)
- Addisons
Increased cellular uptake
- Acidosis
- Tissue breakdown e.g. rhabdomyolysis
Excess load
- Iatrogenic
- Massive blood transfusion
How is urea formed in the body? List 3 causes of a low and high urea.
Urea is formed when ammonia is converted in the liver, and then excreted in the kidneys. It is raised in kidney injury however urea is not specific for kidney disease as there are other causes of abnormal urea.
Causes of high urea:
- dehydration,
- GI bleed,
- increased protein breakdown (surgery, trauma, infection, malignancy),
- high protein intake,
- drugs
Causes of low urea:
- malnutrition,
- liver disease,
- pregnancy
What is creatinine a waste product of?
Creatinine is a waste product of the breakdown of creatine phosphate. It is excreted in the kidneys and is specific for kidney injury (but baseline depends on muscle mass).
How is AKI defined?
An Acute Kidney Injury is when Creatinine rises ≥50% of baseline within 7 days or ≥26μmol/ in 48 hours (or urine output is <0.5ml/kg/hr ≥ 6 hours).
What is ALT? What are the normal ranges?
Alanine Transferase (ALT) is a cytosolic enzyme, which is expressed predominantly in liver cells and is used as a marker to assess liver cell damage.
ALT < 120 IU/L: generally considered mild
ALT > 120 IU/L: generally considered severe
List 3 common causes of raised ALT.
Common causes:
- Alcohol
- Viral hepatitis
- Steatosis
- MEdications toxins e.g. NSAIDs, antibiotics, statins, antiepileptics, antituberculosis drugs
Less common:
- AI hepatitis
- Haemochromatosis
- Alpha-1 antitrypsin deficiency
- Wilson’s disease
Non-hepatic causes of raised ALT (usually small)
- Coeliac
- Strenuous exercise
- Muscle disease
- Endocrine disease e.g. Hypo/hyperthyroidism
What is AST? How can it be helpful alongside ALT? Is it better than ALT? Where is it found in the cell?
Aspartate Aminotransferase (AST)
Ratio of AST to ALT may provide useful information about the possible cause of liver disease: AST:ALT ratio ≥ 2.1 may be suggestive, but not diagnostic of alcohol related liver disease, while AST:ALT ratio < 2.1 may suggest hepatic steatosis or chronic viral hepatitis.
AST is expressed in the liver, as well as in the heart, skeletal muscle, kidneys, brain and red blood cells and therefore is not as liver specific as ALT. ALT is predominantly cytoplasmic and AST is present in both cytoplasm and mitochondria
What is ALP? Where is it found?
Alkaline Phosphatase (ALP)
The two main sources of ALP are liver and bone, although there are also intestinal and placental isoforms. Elevations may be physiological or pathological.
List 3 physiological and pathological causes of a raised ALP?
Physiological:
- Third trimester of pregnancy
- Adolescents, due to bone growth
- Benign, familial
Pathological:
- Bile duct obstruction
- Primary biliary cirrhosis
- Primary sclerosing cholangitis
- Drug induced cholestasis, e.g. anabolic steroids
- Metastatic liver disease
- Bone disease e.g. Paget’s
- Heart failure
What is GGT a good marker for? What is a disadvantage?
Advantage/disadvantage
Gamma-Glutamyl Transferase (γGT) is a sensitive marker for hepatobiliary disease, but its use is limited by poor specificity
The use of γGT is in supporting a hepatobiliary source for other raised liver enzymes, e.g. ALP. It has limited utility as a primary liver test. If an isolated raised γGT is found, consider retesting after 3m if mildly raised (5x ULN). Consider ultrasound if γGT is >5x ULN.
List some causes of raised GGT.
- Hepatobiliary disease (often with other liver enzyme abnormalities)
- Pancreatic disease
- Alcoholism
- Chronic obstructive pulmonary disease
- Renal failure
- Diabetes
- Myocardial infarction
- Drugs, e.g. carbamazepine, phenytoin and barbiturates and oral contraceptive pill
Apart from LFTs which tell us about liver/bile duct damage, which tests can we do to assess liver function?
- Haem breakdown – Bilirubin
- Plasma proteins – Albumin
- Clotting factors - PT/INR
- Portal system – platelets
