Tuesday, June 24, 2014

Advantages and Disadvantages of Testing in Serum, Saliva, Urine or Capillary Dried Blood

Diagnostic testing using body fluids is a cornerstone of modern medicine.  While urine analysis has been used by doctors since the middle ages, blood plasma and serum testing was developed during the last 100 years.  More recently, routine saliva testing for hormones was introduced, followed by commercial testing in capillary dried blood spots.  Dried urine testing has now eliminated some of the disadvantages of liquid urine collections, making this methodology more accessible.

With the innovations in testing methods comes a need to understand which body fluids serve the doctor and patient best in a variety of testing situations.  This is particularly important when testing hormones in patients using supplemental hormones by a variety of administration routes.  The following helps to outline the advantages and disadvantages of each of the commonly-used methods. 

Serum/Plasma - Advantages 

 
·        Accepted as gold standard testing method by the conventional medical community

·        Wide range of hormone tests available: Ideal for testing peptide hormones

·        Automated with FDA-approved methodology

·        Costs covered by most insurance carriers

·        Familiarity with established levels and ranges

Serum/Plasma - Disadvantages

·        Invasive -sharp needle in arm

·        Stressful -inconvenient to patient-requires driving to blood draw station

·        Phlebotomist required

·        Processing of specimen-centrifugation

·        Shipment-Biohazard labeling and requires cold packs

·        Normal ranges (+/- 2 SD) are too wide-more geared for disease than failing health

·        Difficult to measure multiple times during day due to collection logistics

·        Usually measures TOTAL and not BIOAVAILABLE fraction of hormone in bloodstream

·        Limitations with testing of sex hormones: No distinction between bound and free hormone

·        Cannot be used to measure hormone metabolites

·        Not a valid method for measuring hormones delivered topically -gross underestimation of hormone distribution to tissues

Urine  - Advantages 

·        Non-invasive

·        Simple collection procedure

·        Measures total daily output of steroids

·        Measures steroid metabolites

·        More likely covered by insurance carriers

Urine - Disadvantages

·        Problem with 24 hr urine collections: Inaccuracy in collecting all urine-missed collections

·        Inaccuracy in determining volume of urine collected during 24 hours

·        Up to 40% of 24-hour urine collections are done improperly

·        Results altered by liver or kidney disease

·        Diurnal hormone patterns (cortisol). Inconvenient for assessment of monthly variations (estrogen and progesterone)

·        Expensive and advanced testing technology required for better accuracy

Saliva - Advantages

·        Simple

·        Stress-free

·        Noninvasive (no needles)

·        More convenient than blood testing for health care provider and patient

·        Measures the “unbound” biologically active or free hormone levels

·        Ideal for measuring and accurately monitoring transdermal application of hormones

·        Optimized for multiple collections any time of day/month, any place

·        No special processing (eg, centrifugation, ice-packs) prior to shipment

·        Hormones stable in saliva for weeks

·        Ideal for evaluating cortisol secretion patterns, and balance and flow of estrogens and progesterone.

·        Salivary estriol can be tested to identify women at risk for preterm labor: It spikes approximately two weeks prior to the onset of labor

·        Convenient shipment by regular US mail

Saliva - Disadvantages

·        Restricted to steroid hormones-no thyroid or peptide (e.g. FSH, LH) hormones

·        Technically more challenging: need 10-20x sensitivity-more problematic for hormones at very low concentration (i.e., estrogens)

·        Interfering substances - food, beverages

·        Sublingual use of hormones leads to spurious high test results (direct contamination of the oral mucosa)

·        Problematic for those with poor saliva production

·        Restrictions regarding eating, drinking, make-up and brushing teeth

·        Hormone metabolites cannot be measured in saliva

Capillary Dried Blood Spot - Advantages

·        Convenient-Simple collection procedure

·        Can be collected at remote sites - samples are stable when dried

·        More latitude in collection timing than serum-i.e. night time sampling for cortisol & insulin

·        Dried serum analytes very stable for at least a month at ambient temperature-shipping simplified-allows for international shipment without need for Biohazard Label

·        Wider range of analytes can be tested than in saliva - similar to serum/plasma

·        Results & ranges equivalent to serum/plasma for endogenously produced hormones

·        More accurately reflects tissue uptake of exogenously used hormones than serum/plasma (gross underestimation)

Capillary Dried Blood Spot - Disadvantages

·        Finger-prick with a needle inconvenient for some

·        Not all analytes can be tested in dried blood

·        Sometimes sample contamination problems in patients using their hands to apply topical hormones.

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