Clinical Biochemistry of

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Clinical Biochemistry of Metabolic Disorders - I
Dr Vivion Crowley FRCPath FRCPI Consultant
Chemical Pathologist St Jamess Hospital Dublin
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Definition of Diabetes Mellitus (DM)

• DM occurs because of
• Lack of insulin and/or
• Factors opposing insulin action
• It results in a state of increased blood glucose
• (hyperglycaemia)

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Epidemiology of DM

• 3 of UK population affected (90 T2DM)
• 300 million people affected globally by 2025

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Classification of DM
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Pathogenesis of Diabetes

• T1DM
• Immune mediated destruction of pancreatic ß-cells
  
• HLA- associated
• ? Viral antigen/molecular mimicry
• Some genetic predisposition now recognised
• T2DM
• Genetic predisposition, often family hx
• Insulin resistance in liver, muscle, adipose
  tissue
• Pancreatic ß-cell dysfunction

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Obesity is a major risk factor for T2DM
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Criteria for diagnosis of Metabolic Syndrome
Component Defining value
Abdominal obesity WC gt88cm in females gt102cm in males
Elevated fasting Triglyceride gt 1.65mmol/L
Reduced HDL cholesterol lt 1/3mmol/L in females lt1.0mmol/L in males
Elevated BP SBP 130mmHg OR SBP 85mmHg
Elevated fasting glucose 6.0mmol/L
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Waist circumference is a clinically useful
measure of central
adiposity
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Presenting Features of DM

• T1DM abrupt onset, younger age group, Wt loss
  vs. T2DM (obese)
• Osmotic symptoms thirst, polyuria, nocturia,
  blurred vision
• Fatigue, lassitude
• Recurrent infections e.g. fungal infections, UTI
• Macrovascular complications e.g. angina, MI, TIA
• Microvascular complications e.g. visual
  impairment, proteinuria, neuropathy
• Associated conditions e.g. cataracts

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Diagnosis of DM - background

• 1980 - WHO criteria based on OGTT
• (fasting plasma Glucose 7.8mmol/L)
• 1997 ADA new criteria fasting plasma Glucose
  7.0mmol/L
• Increased risk of microvascular and macrovascular
  
• complications above this level
• 1998 WHO adopted ADA level but maintained OGTT
• Fasting and 2h post-glucose load - samples

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WHO Criteria for the diagnosis of DM
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Management of DM

• Healthy lifestyle
• Diet
• Exercise
• Avoid CVD risk factors e.g smoking
• Medications (T2DM)
• Biguanides metformin
• Sulphonylurea
• Thiazolidinediones (TZDs)
• Insulin regimens
• Treating comorbidities
• Hyperlipidaemia, hypertension etc

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What lab tests are used to monitor glycaemic
control?

• Plasma Glucose Fluoride oxalate sample
• Glucometer
• Point of Care Testing devices (POCT)
• finger prick blood spot
• Patient keeps a diary
• Record reviewed in clinic
• Glucometer cannot be used to diagnose
  hypoglycaemia
• Glucose gt 30mmol/L must be checked in lab

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What other lab tests are used to monitor
glycaemic control?

• DCCT and UKPDS trials demonstrated that tight
  glycaemic
• control reduced chronic microvascular
  complications of DM
• HbA1c
• -results expressed as of total Hb (Range lt5.4)
• -indicates glycaemic control over preceding
  6-8weeks
• -variant Hb e.g. HbF, HbS can give misleading
  results
• Increased RBC turnover e.g. haemolytic anaemia
  can
• affect result
• Fructosamine
• -Indicates Glycaemic control over 3-4 week
• -Useful in monitoring brittle diabetic e.g.
  pregnancy
• -Much less commonly used than HbA1c

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Acute complications of DM
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Diabetic Ketoacidosis (DKA)

• Primarily seen in T1DM but increasingly
  recognised in T2DM
• Pathogenesis
• Relative insulin deficiency
• Relative excess effects of catabolic hormones
• e.g. glucagon, catecholamines
• Increased gluconeogensis and glycogenoloysis
• Decreased glucose uptake in muscle
• Increased lipolysis results in ketone body
  formation
• Ketone bodies can be metabolised by brain
• Precipitating factors
• Conditions that result in an excess of catabolic
  hoemones
• e.g. infections, trauma, MI
• omission of insulin due to illness
• 40 of cases no obvious precipitating factors

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Clinical Features of DKA

• Hx of
• T1DM with poor control (younger female patients)
• May be first presentation of T1DM
• Polyuria
• Polydipsia
• Wt loss, fatigue
• Nausea, Vomiting
• Abdominal pain (can have raised plasma amylase)
• O/E
• Drowsiness
• Dehydrated
• Hypotensive
• Tachypnoea (air hunger or Kaussmaul breathing)
• Acteone breath

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HyperOsmolar Non-Ketotic (HONK) coma

• Associated with T2DM
• Pathogenesis
• Relative insulin deficiency
• Excess glucose production
• Decreased glucose uptake
• Hyperosmolar plasma as a result of severe
  hyperglycaemia
• However ketone body production is not a feature ?
  Reason why
• Precipitating factors
• Similar to DKA
• Also may be first presentation of T2DM

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Clinical Features of HONK

• 2-3 week hx of
• polyuria
• polydipsia
• increasing confusion
• O/E
• Obtunded
• Dehydrated
• Hypotensive
• Focal neurological signs

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Biochemistry features of DKA and HONK
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Lactic Acidosis (LA)

• Characterised by
• pH lt 7.35
• plasma lactate gt 5mmol/L

LA associated with biguanides associated with
renal impairment
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Chronic Complications of DM
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Microvascular - Retinopathy
Pre-proliferative
Maculopathy
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Microvascular - Neuropathy

• Diffuse polyneuropathy
• Autonomic neuropathy
• Erectile dysfunction
• Gastroparesis
• Symmetrical sensory neuropathy
• - Can lead to neuropathic ulcers etc
• Mononeuropathies
• Proximal motor (femoral) neuropathy
• Radiculopathies
• Cranial nerve palsies
• Acute painful neuroapthies

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Microvascular - Nephropathy

• Early stage hyperfiltration with increased GFR
• Incipient stage microalbuminuria
• Persistent detectable proteinuria
• Progressive renal failure decreasing GFR
  leading to ESRD
• Detection of microalbuminuria
• Key indicator of diabetic renal disease
• Also an indicator of increased CVD risk in T2DM
• Screening test Albumin-Creatinine ratio
• 2.5mg/mmol/L (Men) and gt3.5 (women)
• Urinary albumin excretion rate

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Pathogenesis of microvascular complications

• Chronic hyperglycaemia may cause
• Accumulation of sorbitol via polyol pathway
• Myoinositol depletion
• Protein glycosylation forming AGE
• (AGE Advanced Glycosylation End-Products)
• AGE can lead to
• Basement membrane damage
• Intracellular protein and DNA damage
• Stimulation of ROS through AGE receptors

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Macrovascular Complications

• Coronary heart disease (CHD)
• Peripheral vascular disease (PVD)
• Cerebrovascular disease
• In CVD risk assessment charts DM is considered
  CVD risk
• Equivalent i.e. must treat risk factors
• Dyslipidaemia
• Hypertension
• Obesity

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Hypoglycaemia

• Definition
• plasma glucose lt 2.8mmol/l (blood glucose lt
  2.2mmol/l)
• Clinical presentation
• Adrenergic features,
• Neuroglycopaenia
• Whipples triad
• Symptoms signs of hypoglycaemia
• Plasma glucose lt 2.8mmol/l
• Relief of symptoms by glucose intake
  (infusion/oral)

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Hypoglycaemia -Aetoiology

• Fasting Hypoglycaemia
• Causes
• Drug therapy - Insulin, Sulphonylurea,
  ?-blockers, Quinine
• Factitious - Insulin, sulphonylureas (healthcare
  workers)
• Insulinoma
• Hepatic failure - gluconeogenesis
• Sepsis, Cardiac failure
• Hypopituitarism, Addisons disease
• Tumour-related hypoglycaemia
• mesenchymal tumours e.g. fibrosarcoma etc.
• ? Ectopic IGF II by tumour cells
• Autoantibodies - Insulin, Insulin receptor

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Hypoglycaemia - Aetiology

• Reactive (post-prandial) Hypoglycaemia
• Hypoglycaemia up to 4 hrs after food intake
• Idiopathic
• Early diabetes
• Post-gastric surgery
• Non-Insulinoma Pancreatogenous Hypoglycaemia
• (adult-onset Nesidioblastosis)

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Hypoglycaemia Biochemical Investigations

• Ensure that
• 1. hypoglycaemia is documented by laboratory
  plasma glucose
• 2. sample collected into a fluoride tube
• 5hour OGTT
• Hypoglycaemia may occur between 2-5 hours after
  glucose load
• This may occur in normal individuals (?
  Significance)
• Definitive investigation for fasting
  Hypoglycaemia
• Supervised - 72 hour prolonged fast
• If pt develops neuroglycopaenic symptoms then
  measure
• Plasma Glucose, Insulin, C-pepetide
• Other routine investigations
• U/E, LFTs, ? Endocrine (R/O Hypopit, Addisons
  disease)

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Clinical Biochemistry and Calcium metabolism
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What are the main factors influencing plasma
calcium levels?

• Plasma Ca
• 50 free (ionised Ca)
• influenced by pH
• 40 bound to protein
• influenced by Albumin and Globulin levels
• 10 complexed to PO4, HCO3, Lactate etc
• influenced by levels of these molecules

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• Parathyroid hormone
• Increases Bone resorption
• Increases Renal Ca reabsorption
• Decreases Renal PO4 reabsorption
• Increases Renal production of 1, 25 (OH)2 VitD
• Net effect Ca PO4

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• Vitamin D - (1,25 (OH)2 Vit D
• Increases bone resorption
• Increases renal reabsorption of Ca and PO4
• Increases GI absorption of Ca and PO4
• Decreases PTH production
• Decreases renal Vit D
• Net Effect Ca PO4

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• Calcitonin
• Net effect Ca PO4
• (? Clinically relevant e.g. MTC no
  hypocalcaemia)
• PTH related Peptide (PTHrP)
• Binds to the PTH receptor similar effects as
  PTH
• Physiological role - ? Involved in Ca regulation
  in pregnancy

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Biochemical Investigation of a Patient with
Suspected Hypercalcaemia
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What are the causes of Hypercalcaemia?

• Hyperparathyroidism
• Malignancy
• The Rest
• Dehydration
• Vitamin A or D toxicosis
• Immobilisation
• Thiazides
• Sarcoidosis
• Dialysis fluid
• Milk-alkali syndrome
• Addisons disease
• Thyrotoxicosis
• Phaeochromocytoma
• Familial Hypocalciuric Hypercalcaemia (FHH)

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What are the clinical features of Hypercalcaemia?

• Mild HyperCa asymptomatic
• Moderate/Severe HyperCa
• CNS lethargy, stupor, coma, psychosis
• GItract anorexia, nausea, PUD, pancreatitis
• Renal Nephrolithiasis, polyuria
• Mus Skel arthralgia, bone pain
• CVS hypertension, ECG changes (shortened Q-T,
  arrythmias)
• Bones, stones, moans, groans

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Does the patient have True Hypercalcaemia?

• What is the local reference range?
• Dehydration
• Venepuncture hamoconcentration
• What is the albumin concetration?
• Calculate correctedplasma Ca
• Corrected plasma Ca Total Ca (40 Albumin
  g/L) x 0.02
• Example
• Ca 2.60 mmol/L (2.15-2.55)
• Alb 50g/L
• CorrCa 2.60 (40-50) x 0.02
• 2.60 0.2 2.4mmol/L

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Further Investigation of a single hypercalcaemic
sample

• Repeat plasma Ca
• Fasting non-tourniquet sample x 2
• If normal monitor repeat in 6 months
• If still elevated then proceed with further
  investigations

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Is the patient on Calcium-raising medications?

• Thiazides
• Vit D or A
• Milk-alkali syndrome
• Lithium
• Discontinue meds and recheck Plasma Ca

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What is the PTH level?

• PTH ref range (15 - 65ng/ml) St Jamess
  Hospital
• If normal or elevated this implies HyperCa is
  PTH-dependent
• (Hyperparathyridism)
• Primary adenoma (85), hyperplasia (14),
  malignancy (1)
• Secondary Vit D deficiency (ESRD)
• Tertiary - ESRD
• FHH
• Hyperparathyroidism is the most common cause of
• HyperCa in the community
• If PTH suppressed the HyperCa is PTH-independent
• Consider other causes

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What is FHH?

• Familial Hypocalciuric Hypercalcaemia
• Charcaterised by
• Mild HyperCa (usually lt 3.0mmol/L)
• Normal or mildly elevated PTH
• Rarely have symptoms related to hyperCa
• Caused by a loss of function mutation in CaSR
• Family Hx of Ca problems or parathyroidectomy
• Need to diagnose to avoid inappropriate
  parathyroidectomy
• Measure FECa in second voided morning urine
  (Random)
• - lt1 in the presence of HyperCa suggestive of
  diagnosis

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Does the patient have evidence of neoplastic
disease

• PTH-independent HyperCa commonest cause is
  malignancy
• Mechanisms
• Humoral HyperCa of Malignancy (HHM) secretion
  of PTHrP
• -Squamous (head/neck, lung), renal, thyroid,
  breast,
• Localised osteolytic HyperCa (LOH)
• - myeloma, leukaemia, breast
• Increased Vit D production (rare)
• - lymphoma
• Malignancy is the most common cause of HyperCa in
  hospitals
• Other investigations serum/urine protein
  electrophoresis,

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Other Causes

• Sarcoidosis Serum ACE
• Thyroid disorders TFTs
• Addisons disease Synacthen test
• Vit D toxicity Vit D levels
• Immobilisation multiple fractures, Pagets
  disease
• NB 90 of HyperCa is caused by PHPT or
  malignancy

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Routine GP sample from 62 yr old female Clinical
details fatigue Ca 2.75 (2.15-2.55) PO4 0.73
(0.8-1.35) ALB 36 (35-40) ALP 104 (30- 120) TP
74 (60-80) Is this true hypercalcaemia? The
PTH is 85 (9-65), so what is the working
diagnosis? What other investigations would you
consider? How would you advise this patient?
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70 yr old male presented with the Hx of Bone
pain and malaise Ca 3.4 PO4 1.5 Alb 30 TP
110 ALP 100 What is the corrected Ca
level? What further investigations would you
consider? The PTH is 10 (9-65), is the HyperCa
PTH dependent or independent? What is the likely
diagnosis?