Lecture 8 - Approach to Clinical Haematological Investigations

Question 1

Deviation from ‘Normal’

Answer 1

Categories

• incorrect measurement
• artefact
• physiological
• pathological (abnormal, atypical)

Question 2

Incorrect Measurement

Answer 2

May occur due to a systemic or random error
Systematic error
- e.g. poorly calibrated analyser, use of incorrect method, use of incorrect reagent etc.
Random error
- e.g. air bubble, clot preventing reagent flow, incomplete wash allowing sample carry-over etc.
In these situations the resultant measurement does not reflect the composition of the sample

Question 3

Artefact

Answer 3

Artefacts = changes in the characteristics of the sample that occurs after the sample is collected and is caused by the collection or handling of the samples
May affect the sample as a whole or a specific component of the sample i.e. RBC, WBC, platelets
Not due to physiological or pathological processes

Question 4

Platelet Artifacts - Aggregation

Answer 4

Aggregation (clumping)
- activation of platelets; venepuncture
- incomplete mixing, EDTA mediated
Detected by:
- automated analysers
- visual review of blood films
Results:
- decreased measured platelets 
- aggregates of platelets may be misclassified as WBC by some analysers -> erroneously increased [WBC]

Question 5

Platelet Artifacts - Thrombocytosis

Answer 5

Automated analysers commonly misclassify small particles as platelets 
Detected by:
- automated analysers
- visual review of blood film
Results:
- artefactual thrombocytosis = falsely increased platelet count
Causes:
- fragmented RBC
- lipid droplets
- protein droplets
- mircoorganisms

Question 6

RBC Artefacts - Agglutination

Answer 6

Physical association of RBC results in 2-several RBC being misclassified as 1 large RBC
Detected by:
- automated analyser
- visual review of blood films
Results:
- falsely decreased RBC count
- falsely increased MCV
- correct [Hb]

Question 7

RBC Artefacts and its Effect on MCV

Answer 7

Increased MCV
- cold agglutinins
- storage
- hypernatremia
Decreased MCV
- excess anticoagulant
- hyponatremia
May also result in altered classification of RBC indices
- e.g. macrocytic instead of normocytic

Question 8

WBC Artefacts

Answer 8

The concentration of WBC may be affected by several artefacts including:
Neutrophil aggregates
- decreased neutrophil concentration
Pseudoleukocytosis
- aggregates of platelets may be misclassified as WBC by some impedance analyser
- increased WBC results

Question 9

WBC Artefact - nRBC

Answer 9

nRBCs may be encountered in the blood for several reasons
Detected by:
- automated analysers
- visual review of blood film
Results:
- falsely increased WBCs
- increased lymphocytes

Question 10

Physiological Influences on Haematology

Answer 10

Physiological factors may affect the haematological values of a patient
These include:
- biological variation
- sex
- ethnicity
- age
- pregnant

Question 11

Physiological Influences on Haematology - Pregnancy

Answer 11

Decreased Hb
- expansion plasma volume -> physiological anaemia of pregnancy
Increased MCV
Increased neutrophils
Decreased ~10% platelets due to ‘incidental thrombocytopenia of pregnancy’

Question 12

Pathological Influences

Answer 12

Alterations in haematological values induced by a disease state
Many causes
Alterations in FBC results and blood film characteristics typically a starting point for investigation

Question 13

Diagnosis

Answer 13

Identification of the nature and cause of a disorder/disease
Differential diagnosis
- a list of possible causes of a disorder/disease
- often ranked from most probable to least probable
Aetiological diagnosis
- the specific cause(s) of a disorder/disease