Laboratory Data

Introduction

Clinical laboratory tests are valuable tools used to

• Differentiate among possible diagnoses
• Confirm a diagnosis
• Assess current status
• Evaluate the response to therapy

when history and physical exam alone are insufficient

Related tests may be grouped together into a set called a profile or a panel, although small differences may exist between institutions panels.

Reference Range

The reference range is a statistically derived numeric range obtained by testing a sample of individuals assumed to be healthy. It is usually established as the mean ± 2 standard deviations.

• Reference ranges can vary between laboratories and facilities due to differences in analytic techniques, reagents and equipment.
• Reference ranges may also differ among populations and may change as new data are published.

The 'normal range' should be used with caution as it takes little account of an individual's age, sex, weight, height, muscle mass or disease state, many of which variables can influence test results.

NOTE: Abnormal values are not always clinically significant, and in some diseases or conditions, values within the reference range can be considered abnormal.

Interpretation Key Points

Baseline results, rate of change and patterns should be considered when interpreting laboratory results.

• A disturbance of one parameter often cannot be considered in isolation without looking at the pattern of other tests within the group.
• A series of values rather than a simple test value may be required in order to ensure clinical relevance and to eliminate erroneous values caused.

Laboratory results must be interpreted in context of the patient and the limitations of the laboratory test.

• The presence or absence of signs and symptoms associated with the medical problem outweighs an isolated laboratory report.

If laboratory error is suspected, the test should be repeated.

• Laboratory error is an uncommon occurrence; however, it can happen.
• Potential causes of laboratory error include technical error, improper calculation, inadequate specimen, incorrect sampling timing, improper sample preservation, food substances affecting specimen, or medication interference with lab tests.

NOTE: May refer Critical Care Pharmacy Handbook for management of abnormalities in plasma sodium, potassium, calcium, magnesium and phosphate.

External Links

• A Manual of Laboratory and Diagnostic Tests, 2014
  
• Basic Skills in Interpreting Laboratory Data, 2017
  
• Henry’s Clinical Diagnosis and Management by Laboratory Methods, 2016
  
• Testing.com
• Mosby’s Manual of Diagnostic and Laboratory Tests, 2017
  
• Oxford Handbook of Clinical and Laboratory Investigation, 2018