The Clinical Benefit of Osmolality Testing | Advanced Instruments
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How clinical labs benefit from osmolality testing

In-house osmolality testing helps clinicians make more timely diagnoses, improve patient care, and reduce healthcare costs for hospitals of all sizes and settings.

Osmolality is a valuable clinical tool used in the diagnosis and treatment of patients.

Osmolality helps ensure proper diagnosis of various conditions such as:

  • Hyponatremia and similar electrolyte disorders
  • Alcohol and toxin ingestion
  • Metabolic acidosis
  • Monitoring of osmotically active drug therapies, and many more1-5

For these conditions, osmolality testing is a quick and cost-effective test to:

  • Expedite patient treatment
  • Mitigate patient specimen stability concerns
  • Enable time-sensitive patient monitoring
  • Ensure full insurance reimbursement1-5

In-house osmolality testing:

Neville R. Dossabhoy, MD, Consultant Nephrologist in Shreveport, Louisiana, acknowledges that cost savings are significant, and the advantages of in-house osmolality testing are evident. For example, the measurement of plasma osmolality helps narrow the list of differential diagnoses in cases of metabolic acidosis from a hundred plus to fewer than a dozen.

“This leads to significant cost savings and a quicker and proper diagnosis and eliminates the patient spending days in an ICU bed waiting for results of several dozen tests,” explains Dossabhoy. “From a cost-analysis point of view, just one or two patient stays in ICU can cost as much as the cost of the instrument that measures osmolality.”

This is only one example in a long list of possible applications from which clinicians, patients, internal medicine, urology, surgery, gynecology, pharmacy, and general Quality Control can benefit.6

Click here for a list of osmolality applications in emergency medicine.

The value of osmolality testing

Dr. Neville R. Dossabhoy, Consultant Nephrologist, shares his experiences regarding the utility of osmolality and the implications of this critical test on quality and cost of patient care.

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Calculated vs. Measured Osmolality

Osmolality can be calculated as well as measured. However, when it comes to objectivity, accuracy, and efficiency, a freezing point osmometer – such as Advanced Instruments’ OsmoPRO® Multi-Sample Micro-Osmometer – is the choice for the measurement of osmolality. Additionally, calculated osmolality formulas (using sodium, BUN, and glucose) do not account for all osmotically active substances potentially present in body fluids, such as methanol, ethanol, and many others. Therefore, the direct measurement of body fluid osmolality with a Freezing Point depression osmometer is the preferred method when reporting osmolality in a clinical setting.7,8

In practice, physicians use both measured and calculated osmolality to determine a patient’s osmolal gap. The difference between measured and calculated osmolality can be diagnostically significant for conditions such as toxic alcohol ingestion and useful for monitoring patients being treated with osmotically active therapies. If a laboratory were to solely provide calculated osmolality, the physicians could not calculate the osmolal gap to screen for foreign substances.8

Calculated Osmolality Measured Osmolality
  • Highly subjective with over 65 equations in the literature
  • Misses toxins and medications that impact osmolality
  • Error could be embedded in each component of the calculation7,8
  • Provides objective measurement
  • Accounts for everything that impacts osmolality, including toxins and osmotically active therapies
  • Has tight tolerances at clinically relevant decision points7,8

Why you should equip your lab with an in-house osmometer

Many clinical labs have recognized the importance of in-house osmolality testing because they realize that processing and delays in lab results associated with sending out samples cost valuable time and money. 

With an in-house osmometer using freezing point depression, you can account for all clinically relevant, osmotically active substances, including toxins and medications. When measured osmolality and calculated osmolality are used in combination, this enables clinicians to determine the osmolal gap.  Measured osmolality, on the other hand, takes a clinical lab beyond the limitations of calculated osmolality by providing the full range of information physicians need for quick and confident diagnoses of body fluid disorders.7,8

Additional Resources

The Importance of Measured Osmolality

For further information on why measured osmolality is an important tool in providing the best care possible for patients, please view our new resource, “The Importance of Measured Osmolality Testing with an In-House Osmometer.”

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  3. Giuliano Soffiati and Davide Giavarina. Stat laboratory testing or autonomy? Clin Chem Lab Med 2010:48(7):927-930
  4. David A. Novis, et al. Continuous Monitoring of Stat and Routine Outlier Turnaround Times. Arch Pathol Lab Med, 2004, Vol 128, pp. 621-626
  5. Adam J. Singer, et al. Introduction of a Stat Laboratory Reduces Emergency Department Length of Stay. Acad Emerg Med Journal. April 2008, Vol. 15, No.4
    “Calculation of osmolality introduced a systematic bias, overestimating osmolality in the lower ranges and underestimating it in the higher ranges … sum of principal serum solutes, compares poorly with direct measurement using standard osmometry.” Vialet, et al. J Neurosurg Anesthesiol. 17. 106-9 (2005).
    “Our study concurs with other investigations that show that osmolal gap can be a useful diagnostic test in conjunction with clinical history and physical examination.” Krasowski, et al. BMC Clin Pathol 12, 1 (2012).