Clinical Biochemistry An Introduction Dr Steve Smith Consultant Clinical Biochemist UHCW

Clinical Biochemistry Meaurement of substances Measured In: Enzymes Metabolites Metal ions Drugs and metabolites Proteins Hormones Vitamins Mutations in DNA & RNA etc Blood, Mainly serum but also cells Urine Cerebrospinal Fluid Faeces Kidney stones Saliva etc Mainly quantitative but also qualitative Measure around 200 substances in house with al least another 200 possible by sending samples to other hospitals. For example due to the relatively low number of paediatric samples we receive many of the complex metabolic tests we send to the Birmingham Children’s Hospital who are funded to provide a specialist paediatric service.

How do we do it? 96% work is fully automated

Reasons for requesting a Biochemistry test Diagnosis (confirmation or rejection of clinical diagnosis) Glucose, TSH Monitoring (Progression or response to treatment) TSH, HbA1C, Lithium, Tacrolimus, PSA Prognosis (Information about the likely outcome) Cholesterol, Lactate Dehydrogenase (teratoma) Screening (detection of subclinical disease) Phenylketonuria, FOBT, Cholesterol

Specimen Collection Obtaining the correct specimen is crucial Blood Samples: Venous or arterial Specimen bottle Transport Time of day Avoid damage to sample

Questions which may be asked on receipt of Laboratory Results ‘If the result is not what I expected can I explain the discrepancy?’ ‘Does it differ significantly from previous results and will change my diagnosis or the way I treat the patient?’ ‘Is it consistent with clinical findings?’ ‘what do I do next?’

How do we identify abnormal biochemistry? 'The Normal Range’ Defines the values of a biochemical test found in healthy subjects against which patient values can be compared. Artificial concept - no clear boundaries exist. Preferred term is 'Reference Interval'

Defining the Reference Interval ‘Normal’ Subjects Test Value -2.5% +2.5%

Some factors which affect reference ranges Age Gender Diet Pregnancy Time of month Time of day Time of year Weight Stimulus Method These need to be borne in mind when interpreting results

Hormone changes during the menstrual cycle

Some factors which affect reference ranges Age Gender Diet Pregnancy Time of month Time of day Time of year Weight Stimulus Method These need to be borne in mind when interpreting results

Diurnal Rhythm of Cortisol

Some factors which affect reference ranges Age Gender Diet Pregnancy Time of month Time of day Time of year Weight Stimulus Method These need to be borne in mind when interpreting results

Monthly variation in 25-hydroxy Vitamin D levels in UK men and women

Some factors which affect reference ranges Age Gender Diet Pregnancy Time of month Time of day Time of year Weight Stimulus Method These need to be borne in mind when interpreting results

Alkaline Phosphatase Reference Intervals 30 – 120 IU/L 80 – 280 IU/L

Ideal Diagnostic Test Concn. ‘Normal’ Diseased Frequency No false positives or negatives

Comparisons with Disease Groups ‘Normal’ Diseased Test Value +2.5% False Negatives False Positives

Comparisons with Disease Groups ‘Normal’ Diseased Test Value False Negatives False Positives

Different Ranges Reference Interval (Range) Therapeutic Range Urea Therapeutic Range Phenytoin Clinical Cut Off Cholesterol, B-Type natriuretic peptide

Comparisons with Disease Groups ‘Normal’ Diseased Test Value +2.5% False Negatives False Positives

Is the change significant?

Is the change significant? A GP measured the serum creatinine of a 41-year-old man newly diagnosed as having diabetes and hypertension. The result was 105 mol/L. Six months later, both conditions were well controlled and the test repeated.

Is the change significant? Investigation Serum creatinine = 118 mol/L (105 mol/L previous) Patient was alarmed at the increase and the GP uncertain whether the change was significant.

Is the change significant? Analytical Variation Biological Variation Extrinsic Time, posture, stress. Intrinsic

Is the change significant? Analyte Level Change required Sodium 140 mmol/L 6 Potassium 4.2 mmol/L 0.6 Urea 5.0 mmol/L 2.1 Creatinine 60 mol/L 18 Calcium 2.40 mmol/L 0.19 Albumin 40 g/L 5

A 4 year old boy was seen in the paediatric out-patients’ department because of hepatomegaly, metabolic acidosis, and growth retardation. Some of his abnormal blood test results are: Glucose 2.0 mmol/L (3.0 – 5.6 ) Uric Acid 610 μmol/L (200 – 430 ) Lactic Acid 3.7 mmol/L (0.5 – 1.5 ) Cholesterol 5.4 mmol/L (<5.0 ) Triglycerides 6.7 mmol/L (0.5 – 1.5)

Finding a low glucose is common in paediatrics and it triggers a whole raft of tests. Hypoglycaemia is a feature of many inborn errors of metabolism

Von Gierke’s Disease This case Glucose-6 phosphatase deficiency Hepatomegaly due to excess glycogen stores Raised urate due to raised lactate Abnormal lipids due to lack of glucose Lactate raised because G6P taken down a pathway to lactate not glucose.

Demonstrates the knock on effects from what a first might appear common; low glucose.