	Male	Female^*
Haemoglobin (g/dL)	13–18.0	11.5–16.5
RBCs (×10¹²/L)	4.5–6.5	4.0–5.8
Hct (%)	0.40–0.52	0.37–0.47
MCV (fL)	84–96	84–96
MCH (pg)	27.0–32.0
MCHC (g/dL)	27.0–32.0
Platelets (×10⁹/L)	150–400
WBCs (×10⁹/L)	4.0–11.0
Neutrophils (×10⁹/L)	2.0–7.5
Lymphocytes (×10⁹/L)	1.5–4.0
Monocytes (×10⁹/L)	0.2–0.8
Eosinophils (×10⁹/L)	0.04–0.4
Basophils (×10⁹/L)	0.0–0.1
Reticulocytes (% or 10⁹/L)	0.5–2.5 or 20–80

* In pregnancy the Hb may fall as low as 9 g/dL in the third trimester. RBCs, red blood cells; Hct, haematocrit; MCV, mean cell volume; MCH, mean cell haemoglobin; MCHC, mean corpuscular haemoglobin concentration; WBC, white blood cell.

Abnormalities

Anaemia: Low haemoglobin

See Table 7.2.

Table 7.2 The anaemias

Polycythaemia: Increased haemoglobin/haematocrit

See Table 7.3.

Table 7.3 Polycythaemia

True polycythaemia	Secondary polycythaemia	Apparent or spurious polycythaemia
Polycythaemia rubra vera, (PRV)	Inappropriate erythropoietin secretion in benign & malignant renal disorders and by some tumours	Secondary to cigarette smoking, obesity, excess alcohol or hypertension

Thrombocytopenia: Platelet count <150 × 10⁹/L

See Table 7.4.

Table 7.4 Causes of thrombocytopenia

Failure of production	Increased consumption	Pseudothrombocytopenia
Drugs & chemicals Viral infection, e.g. HIV Radiation Aplastic anaemia Leukaemia Marrow infiltration Megaloblastic anaemia Liver disease

Idiopathic thrombocytopenic purpura (ITP)

Disseminated intravascular coagulation (DIC)

Infection

Haemorrhage & transfusion

Systemic lupus

Some leukaemias & lymphoma

Heparin

Hypersplenism

Thrombotic thrombocytopenic purpura (TTP)

Haemolytic uraemic syndrome

Caused by clumping: can be excluded by examination of PBS and citrate sample (clumping due to EDTA)

Thrombocytosis: Platelet count >450 × 10⁹/L

See Table 7.5.

Table 7.5 Causes of thrombocytosis

Primary myeloproliferative disorder	Secondary reactive disorder
Essential thrombocythaemia PRV Idiopathic myelofibrosis

Haemorrhage

Acute & chronic infection

Inflammatory disease

Post splenectomy

Trauma/surgery

Iron deficiency anaemia

Malignancy

Leucopenia: WBC <4.0 × 10⁹/L

• It is uncommon for absolute leucopenia to be due to an isolated deficiency of any cell other than the neutrophil.

• The risk of infection is closely related to the absolute neutrophil count.

• Neutropenia – neutrophils <2.0 × 10⁹/L.

• Lymphopenia – lymphocytes <1.5 × 10⁹/L.

See Table 7.6.

Table 7.6 Leucopenias

Neutropenia		Lymphopenia
Congenital causes	Acquired causes
Benign chronic neutropenia (Yemenite Jews & people of African descent) Rare – Kostmann’s syndrome, cyclic neutropenia

Drugs – cytotoxic agents, anticonvulsants, thyroid inhibitors, antibiotics, clozapine, procainamide, hydroxychloroquine, penicillamine, NSAIDs

Post-infectious – usually after viral infection:

• Severe sepsis

• Autoimmune

• Felty’s syndrome (rheumatoid arthritis)

Systemic lupus erythematosus

Corticosteroids

HIV

Test: Group and screen/crossmatch

Indications

• To determine a patient’s ABO blood group, and to screen serum for the presence of antibodies to common red cell antigens.

• To allow provision of appropriate red cell concentrate (RCC) and blood products in order to avoid transfusion reactions.

How it is done

• ‘Group’ – determines which ABO and Rh antigens are present on patient’s red blood cells (RBCs). RBCs are incubated with commercially available antibodies (anti-A, anti-B), which react with antigens if present and cause agglutination. The patient’s serum is then incubated with A and B cells to determine the presence of anti-A and anti-B antibodies. (See Table 7.8)

• ‘Screen’ – utilizes the indirect Coomb’s test (indirect antiglobulin test). Serum is incubated with a wide range of RBCs that together exhibit a comprehensive range of surface antigens. If antibodies are present they will cause agglutination.

• Crossmatch – may be electronic or serological. An electronic crossmatch is used in uncomplicated cases with a negative antibody screen. A serological crossmatch requires RBCs from the donor unit to be incubated with the patient’s serum, which will cause agglutination if the unit is not compatible.

Table 7.8 ABO blood group antigens present on RBC and IgM antibodies present in serum

Interpretation

Data presented as

• A, B or O blood group and Rhesus (Rh) status, e.g. O+, AB−.

Physiological principles

• Blood type is determined by the presence or absence of inherited antigenic material on the surface of RBCs; the ABO blood group system and Rh blood group system are the two most likely to cause harmful immunologically mediated reactions if noncompatible blood is transfused.

• ABO system. The A and B antigens are produced from a common precursor, the H antigen. Either, both or none may be present. Anti-A or anti-B IgM antibodies are produced in the first years of life possibly by sensitization to environmental substances such as food, viruses and bacteria.

• Rhesus system. The most significant Rh antigen is the Rh D antigen, which is either present (Rh D positive, RhD+) or not (Rh D negative, RhD−). IgG and IgM anti-D antibodies are formed in RhD-negative individuals through a sensitizing event.

Management principles

• ABO compatibility. When considering blood group compatibility for transfusion it is the recipient antibodies and donor antigens that are important. For example, group AB individuals have A and B antigens on the surface of their RBCs; their blood serum does not contain any antibodies against either A or B antigen so they can receive blood from any group (in theory, AB being preferable). Blood group O individuals have neither antigen but both anti-A and anti-B antibodies therefore will cause agglutination of the donor RBCs if they are given anything other than group O blood (Table 7.9).

• Rhesus compatibility. An RhD-negative patient with no antibodies could only receive RhD-positive blood once, as this would lead to the formation of antibodies and potentially hazardous transfusion reactions if they were to receive it again. If an RhD-negative woman develops antibodies and becomes pregnant with an RhD-positive child, these antibodies can cross the placenta and cause haemolytic disease of the newborn. Therefore rhesus-positive blood or platelets should never be given to RhD-negative women of childbearing age or patients with rhesus D antibodies. Platelets can be given with anti-D cover in emergencies.

• Plasma compatibility. Donor-recipient compatibility is the opposite of blood compatibility. Type O plasma (fresh frozen plasma, FFP) can only be given to type O recipients; Type AB can be given to individuals of any blood group (Table 7.10).

• There are usually local policies in place for the routine ordering of preoperative G&S or crossmatched blood that take into account the planned surgery, estimated blood loss and need for transfusion.

• Guidelines are available for the transfusion of blood and blood products published by The Association of Anaesthetists of Great Britain and Ireland (AAGBI) and British Committee for Standards in Haematology (BCSH) and advice should be sought from a haematologist where necessary.

Table 7.9 Red blood cell compatibility

Table 7.10 Plasma compatibility

Recipient blood type	Donor plasma must be:
AB	AB
A	A or AB
B	B or AB
O	O, A, B or AB

Laboratory tests of coagulation

Tests: Prothrombin time (PT)/international normalized ratio (INR), activated partial thromboplastin time (APTT) and thrombin time (TT)

Indications

• Part of coagulation screen often ordered preoperatively.

• Assessment of synthetic liver function.

• Assessment of coagulopathy in disseminated intravascular coagulation (DIC) and massive blood transfusions.

• INR used to monitor warfarin therapy.

• APTT used to monitor unfractionated heparin therapy.

• TT used in diagnosis of hypo/dysfibrinogenaemia.

How it is done

• Platelet poor plasma (PPP) obtained from citrated blood sample (9:1 ratio).

• PT/INR – thromboplastin and calcium added to PPP and time to fibrin formation measured by a photo-optical or electromechanical device; this equals the prothrombin time (PT). To standardize results the PT is compared to a reference value, which gives the INR.

• APTT – PPP, phospholipid and calcium are added to kaolin and the time to fibrin formation measured.

• TT – thrombin added to plasma and clotting time measured in seconds.

Interpretation

Normal range/graph

• PT = 10–14 seconds.

• INR = 0.9–1.2.

• APTT = 25–35 seconds.

• TT = <15 seconds.

Physiological principles

• Coagulation was traditionally thought to consist of ‘intrinsic’ and ‘extrinsic’ pathways with a final common pathway. This has now been replaced with the cell-based model of haemostasis which comprises three stages of initiation, amplification and propagation.

• At the site of vascular injury tissue factor (TF) expressed on extravascular cells forms a TF/VIIa complex that activates factors X to Xa and IX to IXa.

• Factor Xa converts factor V to Va and forms a Xa/Va complex on the TF cell, which converts prothrombin to thrombin (initiation).

• Thrombin activates platelets and factors VIII, V and XI.

• Factor VIII circulates in combination with von Willebrand factor (vWF) which acts as a carrier molecule to transport factor VIII to the platelet surface.

• Activated platelets bind cofactors VIIIa and Va with their respective enzymes IXa and Xa to form a prothrombinase complex, which causes a thrombin burst to take place on the surface of the activated platelet (amplification).

• Thrombin converts fibrinogen to fibrin and the haemostatic plug comprised of platelets and fibrin strands is formed (propagation and stabilization).

• Control mechanisms exist to limit fibrin formation to the site of injury including TF pathway inhibitor, the protein C and S system and antithrombin III.

• Disturbances in these mechanisms can lead to thrombotic disorders.

Abnormalities

See Table 7.11.

Table 7.11 Coagulation abnormalities

Prolonged INR	Prolonged APTT	Prolonged TT
Due to deficiency of factor I, II, V, VII or X: • Warfarin anticoagulation therapy • Vitamin K deficiency resulting in deficiency of vitamin K dependent factors II, VII, IX and X • Liver disease • Coagulopathy secondary to DIC ^* • Coagulopathy secondary to massive blood transfusion • Dilutional coagulopathy • High-dose unfractionated heparin therapy • Fibrinogen deficiency • Haemorrhagic diseases of the newborn

Due to deficiency of Factor VIII, IX, XI or XII:

• Unfractionated heparin therapy

• Haemophilia A, B or C (factor VIII, IX or XI deficiency, respectively)

• Lupus anticoagulant (actually prothrombotic but binds to phospholipid in test sample)

• Coagulopathy secondary to DIC

• Coagulopathy secondary to massive blood transfusion

• Von Willebrand disease

Prolonged due to thrombin inhibition:

• Heparin

• Fibrin degradation products (FDP)

• Lupus anticoagulant

* Disseminated intravascular coagulopathy: DIC may complicate massive tissue injury, sepsis and some pregnancy-related complications. The normal anticoagulant and fibrinolytic systems are overwhelmed resulting in disseminated microvascular thrombi with consumption of platelets and coagulation factors leading to a haemorrhagic state. The fibrinolytic system is activated to dissolve the fibrin thrombi, resulting in the formation of D-dimers and fibrin degradation products (FDP), which have a further anticoagulant action.

Further investigations

• Liver function tests.

• Full blood count (FBC) (monitor platelet count on heparin).

• Fibrinogen level to exclude hypofibrinogenaemia.

• Mixing studies to check for possible factor deficiencies or inhibitors.

• Specific factor deficiencies.

• Lupus/anticardiolipin antibodies.

• Fibrin degradation products (FDPs).

Limitations and complications

• Underfilling sample tube alters the anticoagulant:blood ratio of 9:1.

• High or low haematocrit alters the APTT.

• Heparin contamination prolongs PT and APTT.

• Haemolysis, lipaemia, hyperbilirubinaemia and hyperproteinaemia produce errors in the optical endpoint analysis.

• APTT is not suitable for high-dose heparin, e.g. on cardiopulmonary bypass.

Test: Fibrinogen

Indications

• Diagnosis of acquired/hereditary fibrinogen deficiencies.

How it is done

• Most automated analyzers produce a derived fibrinogen level from PT, APTT and TT.

• Clauss method uses a high concentration of thrombin, which is added to dilute patient plasma, converting fibrinogen into a fibrin clot. The amount of fibrinogen in the sample is inversely proportional to the clotting time.

Interpretation

Normal range

1.5–4.0 g/L.

Abnormalities

See Table 7.12.

• <1.0 g/L may be associated with bleeding.

Table 7.12 Abnormalities of fibrinogen

Elevated fibrinogen	Fibrinogen deficiencies
Pregnancy Acute phase reactions

Congenital

Acquired:

• Advanced liver disease

• DIC due to excessive thrombin generation

• Thrombolytic therapy

• Massive blood transfusion

Management principles

• In a bleeding patient if fibrinogen level <1.0 g/L give cryoprecipitate, which contains 350 mg of fibrinogen, factor VIII, von Willebrand factor, factor XIII and fibronectin or fibrinogen concentrate.

• With massive transfusion fibrinogen levels fall rapidly and cryoprecipitate should always be given as well as FFP.

Further investigations

• Usually done in conjunction with a coagulation screen.

• FDPs.

• D-dimers.

Test: D-dimers and fibrin degradation products

Indications

• Diagnosis of DIC.

• Diagnosis of deep vein thrombosis/pulmonary embolism (DVT/PE).

How it is done

• Latex agglutination assay.

• Enzyme-linked immunosorbent (ELISA) assay.

Management principles

• DIC – identify cause, support coagulation with blood, FFP, cryoprecipitate and platelets as necessary.

• Antithrombin concentrates or recombinant activated protein C have also been used.

• Heparin has been used in the treatment of DIC but is controversial.

• DVT/PE – anticoagulation.

Further investigations

• Coagulation screen.

• Fibrinogen.

Limitations and complications

• Not specific.

• Latex agglutination tests are not sensitive to exclude DVT/PE.

• Moderate increases of D dimers in major surgery do not necessarily indicate a pathological state.

• Rheumatoid factor may cause false positives.

Point-of-care tests of coagulation

Test: Activated clotting time (ACT)

Indications

• Monitor high doses of unfractionated heparin used in cardiopulmonary bypass (CPB), interventional radiology, haemofiltration and critical care.

• Assess adequacy of heparin reversal by protamine.

How it is done

• Sample of whole blood added to a glass tube containing an activator and a small magnet and slowly rotated at 37° in the analyzer.

• As the blood clots the magnet is pulled away from a detection switch and this signals the ACT.

• Other devices use a cuvette, which only needs two drops of blood.

Limitations and complications

• ACT is relatively insensitive to low doses of heparin.

• High ACT values of >600 do not have a linear relationship with heparin dose.

• Affected by hypothermia/haemodilution.

• As protamine may affect the ACT, a prolonged ACT after the appropriate dose of protamine should not generally be treated.

• Aprotinin prolongs celite-activated ACT so ACT should be kept >750 seconds; kaolin-activated ACT is unaffected by aprotinin.

Haemoglobinopathies

Test: Sickledex

Indications

• Screening test for sickle cell anaemia/sickle cell trait (see NICE guidelines).

How it is done

• Blood is mixed with sodium metabisulphite, a reducing agent that induces sickling in susceptible cells. These can be viewed under a microscope within 20 minutes.

Interpretation

Data presented as

• Positive or negative test.

Physiological principles

• This is an autosomal recessive condition in which the beta chain of haemoglobin A has valine substituted for glutamine at position 6 (HbS).

• At low oxygen tensions deoxygenated HbS aggregates producing abnormal, rigid ‘sickle’-shaped cells, which can impede blood flow.

• Sickled cells adhere to the vascular endothelium resulting in chronic endothelial inflammation and damage.

• Sickle cells haemolyze resulting in anaemia.

Abnormalities

A positive test indicates presence of HbS but does not differentiate between:

• Sickle cell trait – heterozygous condition HbS/HbA

• Sickle cell anaemia – homozygous HbS/HbS

• Other haemoglobinopathy in which patients are heterozygous for HbS and another abnormal Hb, e.g HbSC.

Management principles

• All patients of African and Afro-Caribbean descent should have screening by Sickledex test prior to anaesthesia if sickle status unknown.

• Eastern Mediterranean, Middle Eastern and Asian people should also be considered.

• Preoperative advice from haematologists with regards to the need for ‘top up’ or exchange transfusion in patients with sickle cell disease. The hazards of exchange transfusion may outweigh the benefits unless the patient is considered high risk for developing a crisis and complications. Preoperative transfusion aims for a haematocrit of 30% and HbS less than 30%.

• Sickling can be induced by hypoxia, acidosis, dehydration, hypothermia and presence of desaturated HbS therefore perioperative management includes keeping patients warm and well-hydrated, administering supplemental oxygen and maintaining an adequate cardiac output.

• The use of tourniquets is controversial and most authorities advise against their use unless absolutely necessary.

• Antibiotic prophylaxis is important as risk of infection is higher.

Further investigations

• FBC and PBS to look for anaemia (normocytic) and characteristic morphological changes.

• Haemoglobin electrophoresis.

• U&E, urinalysis, liver function tests and chest x-ray to investigate signs of end organ damage.

Limitations and complications

• Indicates presence of HbS not the diagnosis of Sickle cell disease.

• Is positive if HbS is more than 20% of total haemoglobin, so has limited use if recently heavily transfused or <1 year old.

Test: Haemoglobin electrophoresis/high-performance liquid chromatography (HPLC)

Indications

• Diagnosis of haemoglobinopathy.

How it is done

• Haemoglobin electrophoresis is performed at an alkaline pH. At this pH, haemoglobin, a negatively charged protein, will migrate to the anode.

• Normal and abnormal haemoglobins separate from each other on the basis of charge and produce distinct bands that also allow quantification.

Interpretation

Data presented as

• Type and percentage of haemoglobins present.

Abnormalities

• Sickle cell disease – HbS present (see Sickledex test).

• Thalassaemia – genetic disorder resulting in abnormal rates of production of alpha and beta haemoglobin chains. The gene/promoter deletions result in a spectrum of clinical conditions ranging from asymptomatic to death in utero.

Management principles

• As above for sickle cell anaemia/trait.

• Obtain haematology advice.

• There are some case reports of difficult intubation associated with thalassaemia due to ectopic marrow expansion in the bones of the face.

Further investigations

• FBC: Sickle cell anaemia, normocytic anaemia.

• Thalassaemias: hypochromic, microcytic anaemia with normal iron levels.

• Other tests may be required (e.g. echocardiogram to assess pulmonary hypertension) after discussion with a haematologist.

Viscoelastic measurement of haemostasis

Test: Thromboelastography/thromboelastometry

Indications

• Point-of-care test of global coagulation.

• Diagnosis of hypo- or hypercoagulability, platelet function and primary/secondary fibrinolysis.

• To guide blood product and antifibrinolytic drug administration.

How it is done

• Two main instruments perform similar assays:

– Thromboelastography (TEG, Haemoscope Corp, IL, USA; Fig. 7.1) results in a thromboelastograph trace

– Thromboelastometry (ROTEM, Pentapharm, Milton Keynes, UK) results in a thromboelastogram trace.

• A small quantity of blood is placed in a heated cup.

• A pin is suspended within the cup connected to a detector system, a torsion wire in the TEG system and an optical detector in the ROTEM system.

• The cup and pin are oscillated relative to each other.

• Initially when no clot exists the motion of the cup does not affect the pin and the resulting trace is a straight line. As fibrin forms characteristic traces are obtained.

• Modifications:

– Addition of ‘activators’, e.g. kaolin, celite or tissue factor, which allow more rapid results

– Heparinase-coated cups to evaluate the effects of exogenous or endogenous heparins

– Functional fibrinogen tests.

Fig. 7.1 TEG cup attached to pin and torsion wire.

Interpretation

Data presented as

• Graphical trace (Fig. 7.2) and descriptive data. See Table 7.13.

Fig. 7.2 TEG trace showing common parameters.

Table 7.13 Nomenclature used for TEG and ROTEM

	TEG	ROTEM
Measurement period		RT
Clot time-latency time from placing blood in cup until clot starts to form (2 mm amplitude)	Reaction time r	Clotting time (CT)
Period from 2 mm to 20 mm Amplitude	K	Clot formation time (CFT)
Alpha angle	α	α
Maximum angle		Clot formation rate (CFR)
Maximum strength	Maximum amplitude (MA)	Maximum clot firmness (MCF)
Time to maximum strength	TMA	MCF-t
Amplitude at set time	A30, A60	A5, A10…
Clot elasticity	G	Maximum clot elasticity (MCE)
Maximum lysis		Maximum lysis (ML)
Lysis at fixed time	LY30, LY60	CL30, CL60