7.1 Interpreting Lab Data

Why monitor laboratory data?

1. Confirm diagnosis of condition e.g. glucose tolerance test in diabetes

2. Assess severity e.g. creatinine levels in renal failure

3. Check treatment response e.g. LFTs (Liver Function Tests) after treatment of acute hepatitis, FBC (Full Blood Count) after withdrawing a drug

4. Select appropriate drug or dose e.g. choice of diuretic in patient with electrolyte abnormalities, confirming lithium dose by therapeutic drug monitoring

5. Warning against contraindicated drugs e.g. use of nephrotoxic antibiotics in patients with severe renal failure

6. Ensures safety when using potentially dangerous drugs e.g. monitoring urea and electrolytes, monitoring INR for patients taking warfarin

7. Identifying disturbances caused by drugs e.g. side effects

8. Identifying asymptomatic imbalances e.g. non-obvious electrolyte disturbances

9. Differentiating between excess and deficiencies

10. Deciding appropriate route of treatment e.g. IV or oral

11. Corresponding with doctors - allows evidence-based clinical decision making

Reference ranges

• Helps us decide whether a result is normal, high or low

• These ranges are only a guide and vary between laboratories, hospitals and countries

• Vary between adult, children, male, female

What is an important principle when treating an imbalanced lab value?

• Always treat the underlying cause

• May be drug-induced = remove / reduce drug

• May be diet-induceded e.g. high cholesterol = modify diet accordingly

What electrolytes move in and out of the cells through the cell membrane?

• Na+ out

• K+ in

How do you monitor fluid balance?

• Measure fluid input vs output using a fluid balance chart

• Accounts for losses e.g. urine, vomiting, diarrhoea

• Measure serum osmolality (concentration of electrolytes in the blood)

Sodium

Hypernatraemia

When do symptoms appear?

What are the symptoms?

Cause?

Treatment?

• >150 mmol/L e.g. thirst, lethargy, irritability, headache, stupor

• >170 mmol/L e.g. seizure, coma, death

Cause:

• Loss of body water - e.g. dehydration, vomiting, diarrhoea, burns, diseases like diabetes insipidus, diabetic ketoacidosis

• Gain of body sodium - drugs e.g. antacids, antibiotics, dispersible tablets, mineralocorticoid effects of steroids, lactulose, methyldopa, oestrogens

Treatment:

Depends on underlying cause:

• Loss of body water - drink water, IV fluids e,g, 5% glucose if severe

• Gain of body sodium - restrict sodium intake, diuretics

What is the key thing to remember with treatment of hypernatraemia?

• Gradual correction

• Too rapid a change in Na+ can cause complications e.g. cerebral oedema

Sodium

Hyponatraemia

When do symptoms appear?

What are the symptoms?

Cause?

Treatment?

• Some patients are asymptomatic

• If sympatomatic, symptoms manifest at around <130 mmol/L E.g. weakness, lethargy, headache, postural hypotension

Cause:

• Loss of body sodium e.g.

  • Gastro-intestinal losses e.g. vomiting and diarrhoea

  • Salt losing kidney disorders

  • Addisons disease (adrenal insufficiency)

• Gain of body water e.g.

  • Drugs e.g. ACEis, carbamazepine, lithium, NSAIDs, SSRIs

  • After surgery or injury

  • Renal disease causing reduced excretion

  • Congestive heart failure

  • Cirrhosis with ascities

  • Very young / old

Treatment:

• Fluid restriction or slow sodium tablets for mild cases

• Diuretic - in case of too much fluid

• IV in severe cases (<120 mmol/L) or water intoxication - sodium chloride 0.9% or hypertonic saline

Potassium

K+ is key for…

• Muscle excitability

• So the main symptoms of K+ imbalances are related to the muscle and heart function

Potassium

Hyperkalaemia

Symptoms?

Cause?

Treatment?

Symptoms:

• Excitability of muscle e.g. cardiac arrythmias, cardiac arrest, muscle weakness

Causes:

• Drugs e.g. K+ sparing diuretics like Spironolactone, ACEis, ARs

• Renal impairments

• Metabolic acidosis

• Tissue breakdown e.g. in surgery, trauma, severe infection

Treatment:

• Ion exchange resins e.g. calcium resonium for mild-moderate cases

• IV calcium gluconate to first stabilise the heart, then IV insulin, and salbutamol if needed for severe cases

Potassium

Hyperkalaemia

Why is IV insulin given as treatment in severe cases?

Draws K+ into the cells with glucose

Potassium

Hyperkalaemia

Why is hyperkalaemia considered a medical emergency?

Due to risk of cardiac death

Potassium

Hypokalaemia

Symptoms?

Cause?

Treatment?

Symptoms:

• Muscle weakness, excessive fatigue, confusion, low blood pressure, cardiac arrhythmias

Causes:

• Drugs e.g. diuretics such as furosemide and thiazides, salbutamol

• GI losses

• Renal impairment

Treatment:

• Sando K effervescent tablets OR Kay-Cee-L solutionfor mild-moderate cases

• IV mixed sodium chloride with potassium for severe case

Calcium

Hypercalcaemia

Symptoms?

Cause?

Treatment?

Symptoms: Muscle weakness, anorexia, constipation, fatigue, headache, psychosis, arrythmias, coma, death

Causes:

• Hyperparathyroidism, renal disease

• Cancer

• Excessive vitamin D doses

• Bone disease e.g. Paget’s

Treatment:

Increase fluid intake

• By mouth if mild

• By IV sodium chloride 0.9% to promote calcium diuresis if severe

Calcium

Hypocalcaemia

Symptoms?

Cause?

Treatment?

Symptoms:

Neuromuscular excitability e.g. cramps, parasthesia, tetany, convulsions at levels <1.6 mmol/L

Causes:

• Hypoparathyroidism, renal disease

• Vitamin D deficiency

• Excessive phosphate administration

Treatment:

• Oral calcium tablets

• IV calcium gluconate if acute tetany is present

Phosphate

Hyperphosphataemia

Symptoms?

Cause?

Treatment?

• No symptoms

Causes:

• Kidney damage e.g. in renal failure

• Cell damage where phosphate is released from inside the cells

• Drugs e.g. calcium, excessive vitamin D, bisphosphonates

Treatment:

• Reduce phosphate intake moderately

• Phosphate binding salts e.g. calcium, aluminium

Phosphate

Hypophosphataemia

Symptoms?

Cause?

Treatment?

Symptoms:

• muscle weakness, rhabdomyolysis, cardiac and respiratory problems, osteomalacia, rickets

• confusion, seizures, coma

Causes:

• Drugs e.g. antacids which impair phosphate absorption

• Malnutrition

• Alcoholism

• Re-feeding syndrome

Treatment:

• Oral phosphate in mild cases

• IV potassium phosphate infusion in severe cases

Magnesium

High magnesium

Symptoms?

Cause?

Treatment?

Symptoms:

• Muscle weakness, CNS and respiratory depression

• Cardiac problems e.g. cardiac arrest, slow heart beat

• Nausea + vomiting

Causes:

• Drugs e.g. laxatives or antacids which contain magnesium » especially in patients with renal impairment as cannot clear magnesium

Treatment:

• Fluids (sometimes with added furosemide) » promotes renal clearance of Mg

• Haemodialysis if patient has renal impairment

• IV calcium gluconate for treatment of cardiac and respiratory symptoms in severe cases

Magnesium

Low magnesium

Symptoms?

Cause?

Treatment?

Symptoms: muscle weakness, contractions, tetany, tremor, convulsions

Causes:

• Drugs e.g. diuretics, aminoglycosides

• Alcohol

• Renal impairment or GI issues e.g. chronic diarrhoea

Treatment:

• Oral Mg supplements in mild cases

• IV Mg in severe cases

• Mg rich foods e.g. bananas, spinach, wheat, nuts, artichokes

What underlying problems do high urea levels indicate?

• Renal failure - kidneys cant clear urea effectively

• Catabolic states where the body is breaking down tissue e.g. fever, starvation, surgery

• GI bleeding - digestive blood is broken down into protein which raises urea levels

• High protein diet - urea is a byproduct of protein metabolism

• Dehydration - reduced kidney perfusion leads to increased urea levels

What underlying problems does high creatinine indicate?

• Renal failure

• Reduced renal perfusion e.g. due to fall in BP, heart failure, fluid loss

• Drug induced e.g. cimetidine, co-trimoxazole, salicylates

Liver function tests

• Not specific to liver disease alone

• Influenced by many factors outside the liver

• Not reliable indicators of liver function

  • If a single LFT is abnormal - other tests needed to confirm

  • If multiple LFTs are abnormal - liver disease is almost certain - but other tests needed to know exactly what is wrong with the liver

• Useful to monitor acute liver recovery e.g. after hepatitis or drug induced liver damage

Liver Function Tests (LFTs)

Bilirubin

Symptoms

Causes

Symptoms:

35 - 50 micromol/L - jaundice

>350 - 500 micromol/L - severe jaundice

Causes:

• Haemolysis - increased breakdown of RBCs

• Hepatocellular damage - liver cannot process bilirubin effectively e.g. in hepatitis or drug induced liver injury

• Cholestasis (aka obstructive jaundice) - where bile flow is blocked e.g. gall stones or tumours

Liver Function Tests (LFTs)

Alkaline Phosphatase (ALP)

Where is it found?

Causes of raised ALP?

• Found in most tissues, especially: liver, bile duct, placenta, bone

• This means ALP levels are not specific to the liver and can indicate damage in other parts of the body e.g. bone disease, pregnancy

• So should check other markers if a raised ALP is seen

Causes of raised ALP:

• Damaged or inflamed tissue e.g. liver disorders, renal failure, bone disease, cancer

• Pregnancy

Liver Function Tests (LFTs)

Transaminases (AST and ALT)

What does AST:ALT ratio indicate?

What do high levels of AST and ALT mean?

• AST : ALT ratio indicates underlying cause

  • In alcohol related liver disease - AST:ALT is 2:1

• High levels of AST and ALT less than 5 times the normal amount = alcohol abuse, hepatitis, cirrhosis

• High levels of AST and ALT more than 5 times the normal amount = seen across a wide range of liver disease so less useful

The key markers of hepatocellular injury are…

The transaminases (AST and ALT)

Liver Function Tests (LFTs)

Gamma-glutamyl transferase (GGT)

Causes of high GGT

• Not specific to the liver

• Elevated levels can indicate a variety of conditions

Causes of high GGT:

• Alcohol abuse

• Liver disease

• COPD

• Myocardial infarction

• Cancer

• Enzyme inducers e.g. barbiturates

Raised ALP + GGT =

Indicates a hepatic condition rather than a bone condition

Liver Function Tests (LFTs)

Prothrombin Time (PT)

What does this reflect?

What does PT depend on?

Factors effecting PT

Treatment?

• Reflects blood clotting

• Prothrombin time depends on vitamin K clotting factors » synthesised in the liver so liver condition is imported

Factors effective PT:

• Chronic biliary tract disorder causing vitamin K deficiency

• Liver cell damage - reduced synthesis of clotting factors

Treatment:

• Water soluble vitamin K (menadiol)

Liver Function Tests (LFTs)

Plasma proteins

Main plasma protein

What does it indicate

When do low albumin levels occur?

• Albumin

• Long half life (around 20 days) - so reflects chronic hepatic impairment rather than acute

• Low albumin levels occur in chronic liver disease

Red Blood Cell Conditions

Anaemia

What is anaemia?

Is anaemia a diagnosis?

How is it interpreted?

Physical symptoms of ALL anaemias?

Causes?

• Reduced Hb level

• Not a diagnosis, but a sign of an underlying issue

• Should be interpreted in the context of a full profile of blood tests, not just the Hb level alone

Physical symptoms of ALL anaemias:

• Fatigue, breathlessness, dizziness, headache

• Pallor of the skin and mucus membranes seen on examination

• Heart irregularities e.g. palpitations, murmurs

Causes:

• Malabsorption e.g. due to alcoholism

• Increased demands e.g. pregnancy

Red Blood Cell Conditions

Anaemia

Measurements which indicate iron deficiency anaemia

• Low serum Hb

• Low ferritin iron

• High iron binding capacity » body trying to maximise iron

Red Blood Cell Conditions

Anaemia

Which drugs can induce iron deficiency anaemia?

NSAIDs - can cause GI bleeds

Red Blood Cell Conditions

Anaemia

Treatment of iron deficiency anaemia

• Oral iron - 100 - 200mg of elemental iron/day, continue for 3 months after Hb normalises

• Note: Different irons salts deliver different amounts of iron

White Blood Cell Disorders

Neutropenia

What is it?

What is unusual about blood tests in patients with neutropenia?

Symptoms?

Causes?

• Reduction of neutrophils - increases risk of infection

• Most other blood tests including Hb appear normal

Symptoms: infections, fever, chills

Causes: drugs e.g. cytotoxics, infections

Treatment: stopping the causative drug, treating the infection, growth factors in severe cases

Platelets

Thrombocytopenia

What is it?

Symptoms?

Causes?

• Reduced thrombocytes - essential for clot formation

Symptoms:

• Possible anaemia due to prolonged bleeding time

• Bleeding into the skin

• Nose bleeds

• GI bleeding

Causes:

• Destruction of platelets in autoimmune conditions

• Certain drugs