Clinical Biochemistry of Metabolic Disorders - I

1. Clinical Biochemistry of Metabolic Disorders - I Dr Vivion Crowley FRCPath FRCPI Consultant Chemical Pathologist St James’s Hospital Dublin

2. 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)

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

4. Classification of DM

5. 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

6. Obesity is a major risk factor for T2DM

7. Criteria for diagnosis of Metabolic Syndrome

8. Waist circumference is a clinically useful measure of central adiposity

9. 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

10. 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

11. WHO Criteria for the diagnosis of DM

12. Management of DM • Healthy lifestyle • Diet • Exercise • Avoid CVD risk factors e.g smoking • Medications (T2DM) • Biguanides – metformin • Sulphonylurea • Thiazolidinediones (TZDs) • Insulin regimens • Treatingcomorbidities • Hyperlipidaemia, hypertension etc

13. 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

14. 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

15. Acute complications of DM

16. 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

17. 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

18. 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

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

20. Biochemistry features of DKA and HONK

21. Lactic Acidosis (LA) • Characterised by • pH < 7.35 • plasma lactate > 5mmol/L LA associated with biguanides – associated with renal impairment

22. Chronic Complications of DM

23. Microvascular - Retinopathy Pre-proliferative Maculopathy

24. 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

25. 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

26. 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

27. 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

28. 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)

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

30. 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)

31. 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, Addison’s disease)

32. Clinical Biochemistry and Calcium metabolism

33. 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

34. Parathyroid hormone • Increases Bone resorption • Increases Renal Ca reabsorption • Decreases Renal PO4 reabsorption • Increases Renal production of 1, 25 (OH)2 VitD • Net effect:CaPO4

35. 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

36. Calcitonin • Net effect:CaPO4 • (? 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

37. Biochemical Investigation of a Patient with Suspected Hypercalcaemia

38. 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)

39. 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”

40. 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/L • CorrCa 2.60 + [(40-50) x 0.02] • 2.60 – 0.2 = 2.4mmol/L

41. 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

42. Is the patient on “Calcium-raising” medications? • Thiazides • Vit D or A • Milk-alkali syndrome • Lithium • Discontinue meds and recheck Plasma Ca

43. 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 - ESRD • FHH Hyperparathyroidism is the most common cause of HyperCa in the community • If PTH suppressed the HyperCa is PTH-independent • Consider other causes

46. 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

47. 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,

48. 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

49. 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?

50. 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?