Blood Tests

Original Editor - John Mitchell

Top Contributors - Rachael Lowe, Lucinda hampton, Scott Buxton, Admin, Kim Jackson, Jin Yoo, Mason Trauger, Evan Thomas, Naomi O'Reilly, Mariam Hashem, WikiSysop and Adam Vallely Farrell

Introduction

Blood tests are one of the most common types of medical test. They have many uses, including assessing general health, checking for an infection, seeing how well specific organs are functioning and screening for certain genetic conditions.

Human blood contains thousands of different chemicals and molecules.

• If blood in a test tube is allowed to stand it separates out into blood cells and the support fluid called plasma. Some tests are done on the blood cells and others just on the plasma.
• Blood also has a unique ability to clot and will normally do so when taken out of the body into a test tube unless an anti-clotting agent is added.
• If clotted blood is tested the fluid left separate from the clotted cells is called serum.
• Separating blood cells from the support fluids can be speeded up by spinning the test tube of blood in a centrifuge at high speed.

Use: 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
  

4 Common “Panels” in Laboratory Blood Testing

1. Complete Blood Count (CBC)

What it measures: A CBC is a collection of tests related to the cells in your blood.  It usually includes the following results:

• White blood cell count (WBCs): the number of white blood cells per microliter of blood
• Red blood cell count (RBCs): the number of red blood cells per microliter of blood
• Hemoglobin (Hgb): how many grams of this oxygen-carrying protein per deciliter of blood
• Hematocrit (Hct): the fraction of blood that is made up of red blood cells
• Mean corpuscular volume (MCV): the average size of red blood cells
• Platelet count (Plts): how many platelets (a smaller cell involved in clotting blood) per microliter of blood

The CBC can also be ordered “with differential.” This means that the white blood cells are classified into their subtypes.

What the CBC is often used for:

• Anemia may be diagnosed if the red blood cell count, hemoglobin, and hematocrit are lower than normal.
• The white blood cell count usually goes up if a person is fighting an infection. Some medications eg corticosteroids, can cause an increase in the white blood cell count.
• If several types of blood cells (i.e. red blood cells, white blood cells, and platelets) are low, this can be a sign of a problem with the bone marrow.

2. Basic metabolic panel (basic electrolyte panel)

What it measures: Common for electrolytes to be ordered as part of a panel of seven or eight measurements - often referred to as a “chem-7,”  and usually includes:

• Sodium
• Potassium
• Chloride
• Carbon dioxide (CO2) (sometimes referred to as “bicarbonate,” as this is the chemical form of carbon dioxide which is more common in the bloodstream)
• Blood urea nitrogen (BUN)
• Creatinine (often accompanied by an estimated “glomerular filtration rate,” or “eGFR”result)
• Glucose

What the basic metabolic panel is often used for:

• Medication side-effects can cause electrolytes eg sodium or potassium to be either too high or too low. These electrolytes are often monitored when people take certain types of medications eg certain blood pressure medications, diuretics.
• Carbon dioxide levels reflect the acidity of the blood. This can be affected by kidney function and by lung function. Severe infection can also change acid levels in the blood.
• Creatinine and BUN levels are most commonly used to monitor kidney function. Both of these measurements can go up if kidney function is temporarily impaired (e.g. by dehydration or a medication side-effect) or chronically impaired. Laboratories now routinely use the patient’s age and creatinine level to calculate an “estimated glomerular filtration rate,” which represents the filtering power of the kidneys. This is considered a better measure of kidney function than simply relying on creatinine and BUN levels.
• Glucose levels represent the amount of sugar in the blood. If they are higher than normal, this could be due to undiagnosed diabetes or inadequately controlled diabetes. If the glucose levels are on the low side ie hypoglycemia, it is often caused by diabetes medications, and may indicate a need to reduce the dosage of these drugs.

3. Comprehensive metabolic panel

What it measures: This panel includes the items above in the basic metabolic panel, and then usually includes an additional seven items ( sometimes referred to as a “chem-14” panel). What the comprehensive metabolic panel is and uses:

• Calcium - Calcium levels are usually regulated by the kidneys and by certain hormones ( not usually a good way to assess calcium intake or total calcium stores in the bones and body). High or low blood calcium levels can cause symptoms, including cognitive dysfunction, and usually indicate an underlying health problem. They can also be caused by certain types of medication.
• Total protein
• Albumin - Albumin is one of the key proteins in the bloodstream. It is synthesized by the liver. Low albumin levels may indicate a problem with the liver or a problem maintaining albumin in the bloodstream. Malnutrition may cause low albumin levels.
• Bilirubin (total) - Bilirubin is produced by the liver, and usually drains down the bile ducts and into the small intestine. Some bilirubin is also related to the breakdown of red blood cells. An increase in bilirubin can be caused by gallstones or another issue blocking the bile ducts.
• Alkaline phosphatase - Found throughout the body, but especially in bile ducts and also in bone. Higher levels are often caused by either a blockage in the liver or by a problem affecting bone metabolism.
• AST (aspartate aminotransferase) and ALT (alanine aminotransferase) - AST and ALT are enzymes contained in liver cells. An elevation in these enzymes often indicates a problem affecting the liver. This can be caused by medications or by a variety of other health conditions.

4. Lipid (cholesterol) panel - measure the different types of cholesterol and related fats in the bloodstream. The panel usually includes:

• Total cholesterol
• High-density lipoprotein (HDL) cholesterol, sometimes known as “good” cholesterol
• Triglycerides
• Low-density lipoprotein (LDL) cholesterol, sometimes known as “bad” cholesterol
• LDL results are usually calculated, based on the other three results

People are often asked to fast before having their cholesterol checked. This is because triglycerides can increase after eating, and this can cause a falsely low LDL to be calculated. Recent finding however concluded that in most cases, it’s not necessary for people to fast; it’s inconvenient and only makes a small difference in test results.

What the lipid panel is often used for - usually to evaluate cardiovascular risk

• Higher than normal total or LDL cholesterol levels are sometimes treated with a medication eg statins. They can also be reduced by dietary changes

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