Podcast
Questions and Answers
Why is the calculated osmolarity of plasma significantly lower than the true osmolality?
Why is the calculated osmolarity of plasma significantly lower than the true osmolality?
What is the effect of increased protein concentration in plasma on the volume of solvent?
What is the effect of increased protein concentration in plasma on the volume of solvent?
What is the unit of measurement of the concentration of ions in plasma according to most methods?
What is the unit of measurement of the concentration of ions in plasma according to most methods?
Why is the molarity of certain ions such as sodium reduced in pseudohyponatraemia?
Why is the molarity of certain ions such as sodium reduced in pseudohyponatraemia?
Signup and view all the answers
What is the purpose of the factor of 2 in the formula for calculating plasma osmolality?
What is the purpose of the factor of 2 in the formula for calculating plasma osmolality?
Signup and view all the answers
What is the effect of increased protein concentration in plasma on the molality of certain ions?
What is the effect of increased protein concentration in plasma on the molality of certain ions?
Signup and view all the answers
What is the term used to describe the apparently low sodium concentration in plasma due to high protein concentration?
What is the term used to describe the apparently low sodium concentration in plasma due to high protein concentration?
Signup and view all the answers
What is the purpose of osmometers in measuring plasma osmolality?
What is the purpose of osmometers in measuring plasma osmolality?
Signup and view all the answers
What is the formula used to calculate plasma osmolality?
What is the formula used to calculate plasma osmolality?
Signup and view all the answers
Why is the volume of solution greater than the volume of solvent in a protein solution?
Why is the volume of solution greater than the volume of solvent in a protein solution?
Signup and view all the answers
Study Notes
Requesting Laboratory Tests
- Laboratory tests should be used judiciously to provide useful information, avoid unnecessary discomfort, and optimize patient care.
- Overinvestigation can be harmful, causing delay in treatment, and wasting resources.
- Before requesting a test, clinicians should consider whether its result would influence their clinical management of the patient.
When is a Laboratory Investigation 'Urgent'?
- A laboratory investigation is considered 'urgent' if an early answer will alter the patient's clinical management.
- Laboratory staff should be consulted and the sample 'flagged' as clearly urgent if the test is required immediately.
Interpreting Results
- When interpreting laboratory results, clinicians should ask:
- Is the result the correct one for the patient?
- Does the result fit with the clinical findings?
- Is the result abnormal when the appropriate reference range is taken into account?
- Is the abnormality of diagnostic significance or a non-specific finding?
- If it is one of a series of results, has there been a change and, if so, is this change clinically significant?
Diagnostic Performance
- Test sensitivity measures the frequency of a test being positive when a particular disease is present.
- Test specificity measures the frequency of a test being negative when a certain disease is absent.
- Receiver operating characteristic (ROC) curves visually express the usefulness of tests.
- The predictive value of a negative result is the percentage of all negative results that are true negatives.
Test Reference Ranges
- A reference range (or interval) usually includes 95 per cent of the test results obtained from a healthy and sometimes age- and sex-defined population.
- For most tests, the individual's results for any constituent are distributed around the mean in a 'normal' (Gaussian) distribution.
- The 95 per cent limits are about two standard deviations from the mean.
Pseudohyponatraemia
- Pseudohyponatraemia occurs when the concentration of proteins in plasma is markedly increased, reducing the volume of solvent but not the volume of solution.
- This can cause the molarity (mmol/L) of certain ions, such as sodium, to be reduced, but the molality remains unchanged.
- A formula can be used to calculate plasma osmolarity, taking into account the concentrations of sodium, potassium, urea, and glucose.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz covers the importance of laboratory tests in diagnosis, including when to request urgent tests and how to interpret results.
