Blood Tests

An Introduction To Pathology

Different clinical areas which can be tested:

  • Pathology
  • Biochemistry
  • Haematology (blood bank)
  • Microbiology
  • Histology
  • Cytology
  • Immunology

Use of Pathology Tests

Differential Diagnosis: to confirm or refute
Prognosis: risk factors
Monitoring: progress & treatment
Screening: subclinical presence of pathology

Interpretation

Is it normal?
Is it different?
Is it consistent with clinical findings?

Factors affecting results

  • Age and stage of development
  • Ethnicity
  • Sex
  • Pregnancy
  • Posture
  • Exercise
  • Stress
  • Nutritional state
  • Time
  • Other medical intervention

Chemical Pathology

NB reference ranges apply to adults only and are laboratory-specific and not applicable to every lab result

Water and sodium

Na: 135-145 mmol/l

↓Na - Hyponatremia (from skin, kidneys, gut) – weakness, postural hypotension, syncope, wt loss, cv changes, decreased skin turgor.
↑Na - Hypernatremia (incr. intake, decr. Excretion) – oedema, pulmonary oedema, HT, effusions

Potassium

K: 3.4-5.2 mmol/l

↓K- Hypokalemia (alkalosis, RF, D&V,diuretics) – Weakness, ileus, hypotonia, confusion, depression, arrhythmias, alkalosis.
↑K- Hyperkalemia (catabolism, acidosis, RF) – Cardiac arrest with VF.

Renal Function Tests - Urea & creatinine

U: 2.5-6.5 mmol/l Cr: 60-120μmol/l

Both should rise together in renal failure. Creat is the more accurate measurement, urea is affected more by diet and dehydration.
Creatinine Clearance Crcl: 100-120mls/min
Measures glomerular filtration rate and permeability

Enzymes

  • Non-specific
  • Have a specific time window of elevation
  • Temperature specific

Alkaline phosphatase

alk: 30-120 IU/l

  • ↑ - Pagets, osteomalacia, bone tumours, healing #, osteomyelitis.

Cholestasis, cirrhosis, hepatitis, liver tumour.

Alanine transaminase

Alt/GPT: <40 IU/l

  • ↑ - Acute and chronic hepatitis, liver necrosis, tissue hypoxaemia and crush injuries, cholestasis & other liver diseases.

Creatine kinase CK: ♂40-215 ♀40-185 IU/l

  • ↑ - MI, rhabdomyolisis, Sk. Muscle trauma, MD, severe exercise

Enzymes and MIs

  • -Troponin T (Trop T) rises within hours & remains elevated for days. Results reported as neg, pos or some myocardial damage.

-CK:

  1. At 3hrs, 25% of MIs have raised CKs
  2. At 6hrs, 72% “ “ “ “ “
  3. At 9hrs, 97% “ “ “ “ “

Gamma glutamyl tranferase

γGT/GTP: ♂<65 ♀<55 IU/l

  • ↑ Liver disease esp. Cholestasis, alcoholic liver disease, cirrhosis, hepatitis

Amylase

Amy: <100 IU/l

  • ↑ Acute pancreatitis

other abdo disorders, RF

Thyroid diseases

Hyperthyroidism (Graves disease, multinodular goiter, adenoma) – weight loss, sweating, palpitation, angina, tremor, diarrhea, muscle weakness, goiter, eyelid retraction.

Hypothyroidism (Hashimotos disease, post surgery, congenital, secondary to pituitary/hypothalamic disease)
- lethargy, cold intolerance, dry coarse skin & hair, hoarseness, wt gain, slow reflexes & muscle relaxation. Others including: anaemia, psychosis, constipation bradycardia, CTS, infertility.

Thyroid Function Testing:

TSH 0.3-5mU/l

>15mU/l - 1° hypothyroidism

0.3-5mU/l - euthyroid (normal)

<0.3mU/l - Further investigations!

Interpretation complicated by:
-Many medications, hormones
-Any acute illness – “sick euthyroidism” all thyroid tests are low.
-Recovery – TSH raised.

Glucose:

Fasting 3-5.5 mmol/l
>7.8 – diagnostic of DM
5.5-7.8 – impaired glucose tolerance  

Hyperglycaemia
Thirst, polyuria, dehydration, hypotension, tachycardia, drowsiness.
(and for IDDM, DKA) ketosis, hyperventilation, vomiting.

Hypoglycaemia
Tiredness, confusion, detachment, ataxia, blurred vision, dizziness, paraesthesia, hemiparesis, convulsions, coma

Lactate

<2.0 mmol/l
↑ mainly due to tissue hypoxia (decreased perfusion or decr. PO2)

Albumin

alb: 36-50 g/l

  • Maintains oncotic pressure (keeps fluid in vessels)
  • Transports small drugs, calcium & hormones
  • ↓ (Many causes incl. malnutrition, liver disease, overhydration, incr. cap. Permeability, protein-losing states, burns, haemorrhage, general catabolism-sepsis, fever, malignancy, trauma)
  • Symptoms – edema! (Unresponsive to diuretics or elevation)

C-reactive protein

CRP: <5mg/l

An ‘acute phase’ protein
-Monitoring infections (>100, more likely to be bacterial)
-Distinguishing between AI diseases and active infection
-Monitoring RA Rx
-Checking for post-op infection
More sensitive than ESR

Uric acid

0.1-0.4 mmol/l

Incr. production/decr. Excretion → gout (exquisite pain and inflammation often in 1st MTP joint)
>0.54 mM → 50% chance of developing gout

Tumour Markers
 

  • Chemicals related to the presence/progress of a tumour
  • Either secreted by tumours or cell surface antigens
  • Of greater prognostic than diagnostic use, should always be interpreted in the light of clinical and other diagnostic findings.

Carcinoembryonic Antigen

CEA 2-5μg/l

  • Monitoring/detection of colorectal, gastric, breast, bronchial, bronchial and some ovarian cancers.
  • Modestly elevated levels in a variety of non-malignancies

Alpha Fetoprotein

AFP <9 KU/l

  • Monitoring/detecting liver cancers, testicular cancer.
  • Also raised in pregnancy, hepatic regeneration.

Human Chorionic Gonadotrophin

βHCG <5IU/l

  • Diagnosis and monitoring of choriocarcinoma, also testicular tumours.
  • Also used to detect ectopic pregnancies.

Prosate Specific Antigen (PSA)

  • Monitoring/detecting prostate cancer
  • Maybe raised in benign prostatic hypertrophy

CA 125

<35 IU/l

  • 96% of patients with ovarian cancer have raised levels

CA 19-9

<60 IU/l

  • Elevated in patients with pancreatic tumours

CA15-3

  • Elevated in 70% of patients with metastatic breast cancer. A good marker for monitoring Rx.

Paraproteins

  • Elevated in 98% of patients with myeloma (and other malignancies of B-cells.
  • Myeloma is a haematological malignancy the symptoms of which are anaemia, bone pain (esp LBP) and pathological #s.

Immunology

Anti-nuclear antibody (ANA)

Associated with “connective tissue disease” positive in 95% of SLE, also found in JCA, Sjogren’s syndrome, fibrosing alveolitis

Anti-mitochondrial antibodies (AMA)

positive in >95% of primary biliary cirrhosis.

Anti-smooth muscle antibodies (ASMA)

Positive in 50-70% of autoimmune “lupoid” hepatitis.

Rheumatoid factor (RF)

(anti-IgG antibodies) Positive in 70% of RA (but lots of false positives). Should only be used to screen, NOT monitor, (use C-RP instead)

Anti-Reticulin Antibodies.

-Present in Coeliac disease. Also Crohn's and UC.

Anti-acetylcholine receptor antibody

Positive in 80-95% MG

Anti-cardiolipin antibody

Anti-phospholipid syndrome (recurrent abortion, thromboses, thrombocytopaenia)

Anti-dsDNA antibody

Strongly suggestive of SLE

Anti-ENA (extractable nuclear antigen) Antibody

Used to classify connective tissue diseases

Anti-Intrinsic Factor antibody

Positive in 70% of pernicious anaemia

Anti-neutrophil cytoplasmic antibody (ANCA)

Granulomatosis with Polyangiitis, Microscopic polyangiitis

Anti-thyroid antibody

95% positive in Hashimotos thyroiditis
90% positive in primary myxoedema
18% positive in Graves disease

Haematology

Coagulation studies -Measure the clotting mechanisms, for diagnosis and extent of disorder.

Heparin

Therapeutic administration

  • DVT, PE
  • MI, Unstable Angina

Prophylactic administration

  • >30 mins GA with post-op bed rest.
  • High risk patients.

Pregnancy - Relevant side effects

  • Haemorrhage
  • Thrombocytopaenia

Monitoring of Heparin

Low dose subcut. –
no laboratory control required
Continuous iv infusion or full dose subcut. –
APTT (activated partial thromboplastin time) should
be between 50-75 seconds. Caution with high values
(>100) re spontaneous bleeding.

Warfarin

  • Patients require close monitoring of INR (International Normalized Ratio).
  • Target INR ranges are 2-3 for moderate anticoagulation and 3-4.5 for more intensive therapy.
  • These doses may fluctuate with no clinical significance.


Warfarin requirements may be dramatically changed by:

  • Illness
  • Change in diet
  • Change in other medication


International normalized ratio (INR)
>10 Life threatening haemorrhage can occur.

>4.5 Caution re spontaneous bleeding
-Always be wary of patients with mild haemorrhage such as haematuria or epistaxis (nosebleed).

Full Blood Count (FBC)

Red blood cell count (RBC)

♂4.5-6.5 ♀3.5-5.8

↓anaemias, Hodgkins disease, myeloma, leukaemia, haemorrhage, SLE, rheumatic fever and chronic infection.
↑polycythaemia, renal disorders, decr. plasma vol: (severe burns, shock, vomiting)

Haemoglobin (Hb)

♂13-18 ♀12-16

↓anaemia, hyperthyroidism, liver/kidney disease, many CAs (especially haematological) SLE
↑haemoconcentration disorders: burns, polycythaemia, COPD, CCF.
<5 can lead to MI
>20 can lead to clogging of capillaries.

White blood cell count (WBC)

A useful guide to the severity of a disease process
Neutrophils 2.5-7.5
Lymphocytes 1-3.5
Monocytes 0.2-0.8
Eosinophils 0.04-0.4
Basophils 0.01-0.1

Neutrophilia(↑) bacterial infections, gout, uraemia, poisoning, haemorrhage, haemolysis, necrosis.
Neutropaenia(↓) bacterial infections (poor prognosis) viral infections, certain anaemias, blood cancers, anaphylactic shock.
Eosinophilia(↑) Allergic reactions, parasitic diseases, certain blood cancers, skin infections, immunodeficiency disorders.
-Other variations occur in the specific white blood cell differential count with conditions such as: anaemias, blood cancers, infections, and certain inflammatory disorders.

Platelets (150-400)

Thrombocytosis(↑) malignancies, polycythaemia, RA & other inflammatory diseases, acute infections,
Thrombocytopaenia(↓) toxic affects of drugs, esp. chemotherapy, allergies, anaemias, viral infections, post transfusion, ITP.
Caution with low values re spontaneous bleeding, and bruising.

References