Clinical Biochemistry of Metabolic Disorders - I

Dr Vivion Crowley FRCPath FRCPI

Consultant Chemical PathologistSt James’s HospitalDublin

Definition of Diabetes Mellitus (DM)

DM occurs because of

1. Lack of insulin and/or2. Factors opposing insulin action

It results in a state of increased blood glucose (hyperglycaemia)

Epidemiology of DM

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

Classification of DM

Pathogenesis of Diabetes

T1DM -Immune mediated destruction of pancreatic β-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 β-cell dysfunction

Obesity is a major risk factor for T2DM

Criteria for diagnosis of Metabolic Syndrome

Component Defining value

Abdominal obesity WC >88cm in females

>102cm in males

Elevated fasting Triglyceride > 1.65mmol/L

Reduced HDL cholesterol < 1/3mmol/L in females

<1.0mmol/L in males

Elevated BP SBP ≥ 130mmHg OR

SBP ≥ 85mmHg

Elevated fasting glucose 6.0mmol/L

Waist circumference is a clinically useful measure of central adiposity

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

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

WHO Criteria for the diagnosis of DM

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

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 > 30mmol/L must be checked in lab

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 <5.4%)-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

Acute complications of DM

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 hoemonese.g. infections, trauma, MI•omission of insulin due to illness•40% of cases no obvious precipitating factors

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

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

Clinical Features of HONK

2-3 week hx of •polyuria •polydipsia •increasing confusion

O/E

•Obtunded •Dehydrated•Hypotensive•Focal neurological signs

Biochemistry features of DKA and HONK

Lactic Acidosis (LA)

Characterised by •pH < 7.35 •plasma lactate > 5mmol/L

LA associated with biguanides – associated with renal impairment

Chronic Complications of DM

Microvascular - Retinopathy

Pre-proliferative Maculopathy

Microvascular - Neuropathy

Diffuse polyneuropathyAutonomic neuropathy -Erectile dysfunction-Gastroparesis

Symmetrical sensory neuropathy- Can lead to neuropathic ulcers etc

Mononeuropathies

Proximal motor (femoral) neuropathyRadiculopathiesCranial nerve palsies

Acute painful neuroapthies

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 >3.5 (women)•Urinary albumin excretion rate

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

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

Hypoglycaemia

Definition•plasma glucose < 2.8mmol/l (blood glucose < 2.2mmol/l)

Clinical presentation •Adrenergic features, •Neuroglycopaenia

“Whipple’s triad”•Symptoms & signs of hypoglycaemia•Plasma glucose < 2.8mmol/l•Relief of symptoms by glucose intake (infusion/oral)

Hypoglycaemia -Aetoiology

Fasting Hypoglycaemia

Causes:

Drug therapy - Insulin, Sulphonylurea, -blockers, QuinineFactitious - Insulin, sulphonylureas (healthcare workers)InsulinomaHepatic failure - gluconeogenesisSepsis, Cardiac failureHypopituitarism, Addison’s disease

Tumour-related hypoglycaemia •mesenchymal tumours e.g. fibrosarcoma etc.•? Ectopic IGF II by tumour cells

Autoantibodies - Insulin, Insulin receptor

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)

Hypoglycaemia – Biochemical Investigations

Ensure that 1. hypoglycaemia is documented by laboratory plasma glucose2. 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 investigationsU/E, LFTs, ? Endocrine (R/O Hypopit, Addison’s disease)

Clinical Biochemistry and Calcium metabolism

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

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

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

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

Biochemical Investigation of a Patient with Suspected Hypercalcaemia

What are the causes of Hypercalcaemia?Hyperparathyroidism

Malignancy

“The Rest”

•Dehydration•Vitamin A or D toxicosis•Immobilisation•Thiazides•Sarcoidosis•Dialysis fluid•Milk-alkali syndrome•Addison’s disease•Thyrotoxicosis•Phaeochromocytoma

•Familial Hypocalciuric Hypercalcaemia (FHH)

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”

Does the patient have “True Hypercalcaemia”?

“What is the local reference range?”

Dehydration

Venepuncture – hamoconcentration

What is the albumin concetration?

Calculate “corrected”plasma 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/LCorrCa 2.60 + [(40-50) x 0.02]

2.60 – 0.2 = 2.4mmol/L

Repeat plasma Ca

Fasting non-tourniquet sample x 2

•If normal monitor – repeat in 6 months

•If still elevated then proceed with further investigations

Further Investigation of a single hypercalcaemic sample

Is the patient on “Calcium-raising” medications?

Thiazides

Vit D or A

Milk-alkali syndrome

Lithium

Discontinue meds and recheck Plasma Ca

What is the PTH level?

PTH ref range (15 - 65ng/ml) – St James’s 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 - ESRDFHH

Hyperparathyroidism is the most common cause of HyperCa in the community

If PTH suppressed the HyperCa is PTH-independent

Consider other causes

What is FHH?

Familial Hypocalciuric Hypercalcaemia

Charcaterised by

•Mild HyperCa (usually < 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)- <1% in the presence of HyperCa suggestive of diagnosis

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) - lymphomaMalignancy is the most common cause of HyperCa in hospitals

Other investigations: serum/urine protein electrophoresis,

Other Causes

•Sarcoidosis – Serum ACE

•Thyroid disorders – TFTs

•Addison’s disease – Synacthen test

•Vit D toxicity – Vit D levels

•Immobilisation – multiple fractures, Paget’s disease

NB: 90%+ of HyperCa is caused by PHPT or malignancy

Routine GP sample from 62 yr old femaleClinical 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?

70 yr old male presented with the Hx of Bone pain and malaise

Ca 3.4PO4 1.5Alb 30TP 110ALP 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?