Best Tests March 2006
|Including:Full colour PDF of ‘best tests’ September 2006.|
The Laboratory Investigation of Tiredness
The investigation of tiredness is a clinical rather than laboratory task
- Patients present with tiredness due to lifestyle, psychosocial, and physical causes: these often overlap and interrelate
- The key role of laboratory tests is in the diagnosis or exclusion of physical causes of tiredness
A focused approach to laboratory investigation of tiredness is usually determined by clinical findings
- Define the problem from the patient’s viewpoint
- Focused symptom review: especially looking for red flags
- Focused examination considering patient demographics and history
- Focused laboratory tests determined by clinical findings
Below is a consensus approach that has been suggested for investigating tiredness. There are few clinical trials that assess laboratory testing using patient benefits as outcomes.
|Patients under 50 years without other risk factors:|
Searching for iron deficiency, macrocytosis, significant infections and leukaemias.
|Patients under 50 years with risk factors for the following conditions may require extra tests:|
|Type II diabetes||Fasting glucose||Renal impairment||Creatinine with eGFR
|Thyroid dysfunction||TSH||Body fluid transfer||HIV
Hepatitis B & C serology
|Patients over 50 years OR tiredness lasting over one month|
This wide range of tests reflects the increased risk that older people have of many diseases and the difficulty of reaching a diagnosis in chronic tiredness.
When tiredness is the sole clinical finding, investigations are determined by patient demographics, presence of risk factors and duration of the tiredness.
- bpacnz recommends that, for patients under 50 years in whom tiredness of less than one month’s duration is the sole clinical finding, ferritin is usually the sole initial test of iron status.
- A ferritin below the lower limit of the reference range has a high probability of iron deficiency. In addition, there is some evidence that non-anaemic women with unexplained fatigue and a ferritin towards the lower end of the reference range may benefit from iron supplementation (Verdon, 2003). This does not mean that every woman with a ferritin at this level will benefit from iron therapy.
- Concurrent inflammation will often elevate ferritin, making it more difficult to interpret. Full iron studies may clarify the situation. However, as the concentration rises above 100 μg/L iron deficiency becomes less probable.
- Iron and transferrin saturation are of value:
- When iron overload is suspected
- When adherence to iron therapy is being questioned
- When ferritin is elevated
- When other co-morbidities are known or suspected