Nutrition 411: Why Worry about Body Weight Measurements?

     A healthy person can do a weight check by stepping on a bathroom scale. When a patient is infirm and unable to stand freely on a scale or has other medical problems, the process of obtaining a body weight measurement is not quite as simple. A patient’s debility, impaired cognitive status, and ability to ambulate all affect a caregiver’s ability to perform this seemingly easy task. However, accurate body weight measurements are critical to good wound care, so weighing patients regularly and accurately must be part of care in every medical clinic and healthcare facility.

The Importance of Accurate Weight Measurements

     Healthcare staff often ask, “Is a patient’s body weight really that important?” Absolutely! Registered dietitians (RDs) utilize the body weight measurement as part of the data entered in mathematical formulas that estimate a patient’s total daily energy requirement (TER). In other words, a patient’s weight is part of the information needed to determine the daily caloric requirements necessary to maintain energy balance and promote wound healing. Protein and fluid requirements also are based on body weight. Using a patient’s weight and height, RDs calculate nutritional needs based on each patient’s unique body size and medical condition. This information then is used to develop a nutrition plan of care; thus, an inaccurate weight may result in inappropriate treatment of a patient.

     In many clinical settings, particularly in long-term care, body weight measurement is the least expensive and most readily available way to determine nutrient needs. Some medical facilities use indirect calorimetry rather than body weight to measure TER.1 This technique involves measuring oxygen consumption and carbon dioxide production using a small machine that requires a patient to breathe into a mask. Indirect calorimetry is thought to be more accurate than body weight to establish energy needs of a patient.2 Even if calorie needs are measured using indirect calorimetry, an accurate body weight is still required in order to estimate protein and fluid needs.

     Weight measurements are important in other ways. In acute care and critical care settings, body weight is used to determine or adjust the dosage of certain medications.3 For this reason, inaccurate weights may have profound effects on patient outcomes. In skilled nursing facilities, body weight measurements are tracked at regular intervals. RDs look for both significant weight loss (rapid weight loss during specified time periods) and insidious weight loss (slow weight loss over time). Table 1 outlines the parameters for evaluating the significance of weight loss.

     Weight loss can signal that a patient’s nutritional needs are not being met. Unintended weight loss over time is a risk factor for pressure ulcer development4 and usually means that some type of nutrition intervention is needed. Figure 1 exemplifies a slow weight loss that might not be as easy to identify (but just as detrimental) as a significant weight loss. Unintended weight gain may be a sign of serious medical conditions such as heart or kidney failure or ascites associated with cirrhosis of the liver. Figure 2 details the formula for determining percentage of weight loss.

     Weight measurements are required in many medical facilities to ensure compliance with state and federal regulations. Both hospital and long-term care surveyors are likely to scrutinize a facility’s policies and procedures for weighing patients. Regulatory agencies also look closely at the systems in place to intervene when unintended weight changes occur. In the event of litigation, the timeliness and accuracy of a patient’s weight can be used as an indicator of patient care. For all of these reasons, measuring patient weight correctly is critical in any healthcare setting.

Protocols for Weighing Patients

     Every inpatient medical facility should have a policy in place that clearly delineates the process for obtaining body weight measurements. Today’s standards typically call for obtaining a weight measurement on admission and at regular intervals until an accurate weight pattern is established. Transcribing past weight measurements from prior medical records or asking patients to state their weight are practices that should be avoided. Stated, or verbal weights, are notoriously inaccurate and lead to documentation problems later when a patient actually is placed on a scale. For example, when the nursing assistant asked Mr. J. how much he weighed, he stated 150 lb. This weight was recorded in the medical record. A few days later, it was noted that Mr. J. had a fever and was not eating well. He was placed on the scale and weighed 135 lb. The medical record showed a 15-lb weight loss in only a few days, which was unlikely but probably due to the inaccurately stated weight. This type of error is difficult to explain to surveyors and attorneys. The situation could be easily averted by having and following a policy to avoid stated weights. If a patient exercises his right to refuse to be weighed and a verbal response is all the information available, it should be clearly indicated in the medical chart.

     Most long-term care facilities weigh new patients weekly for 4 weeks and monthly thereafter if the patient’s weight is stable. If weight loss or gain is noted from month to month, the patient should be reweighed as soon as possible, preferably the same day or the next day. If significant weight changes or a slow upward or downward weight trend is noted, the patient should be placed on more frequent monitoring, usually weekly, to help measure the effectiveness of interventions. Certain patients may require daily weighing — eg, when information is needed to assess the effects of medications such as diuretics.

     Facilities often find it hard to make time for daily, weekly, and monthly weighing. Facility or unit managers should emphasize the importance of weight monitoring to staff and conduct routine monitoring to ensure weights are taken as scheduled. It is recommended that outpatient clinics and doctor’s offices, especially wound care clinics, weigh patients at each visit and track weight changes over time.

Selecting the Correct Scales

     Patients can be weighed easily and accurately when the proper scales are available. Each medical facility should have a scale that will allow enough flexibility to accommodate all patients, regardless of patient weight or ambulatory status. Stand-on scales aren’t practical in many healthcare facilities because they can’t accommodate wheelchair or bed-bound patients. Chair scales (with chair attached) are available for patients who cannot stand; however, a patient must be transferred to the scale’s chair for weighing. Some scales allow a wheelchair to be wheeled up onto the scale so transferring is not needed. In this situation, the patient’s wheelchair must be weighed when empty and subtracted from the weight of the patient and chair together in order to get an accurate patient weight. Bed-bound patients can be weighed without being transferred using either a bed scale or a sling scale. Bed scales are placed underneath a bed and the weight of the bed is subtracted to obtain the patient’s weight. To use a sling scale, the sling is carefully placed underneath the patient. The patient is lifted off the bed using the sling and weighed. Once the weight is obtained, the patient is returned to the bed.

     Many healthcare facilities treat bariatric patients on a regular basis. Stand-on scales that hold up to 1,000 lb are available, as are extra-wide wheelchair scales. Any facility that accepts bariatric patients should be equipped with scales that can accommodate these persons without compromising their dignity.

     Scales are delicate instruments that must be handled gently and regularly maintained in accordance with the manufacturer’s instructions; they must be calibrated frequently. To test a scale, weigh something with a known weight, such as a 10-lb weight from the physical therapy department. A scale that does not measure the weight accurately should be recalibrated. Every facility should have a policy that outlines the preventive maintenance procedure for the scale and a log to support that the policy has been followed.

Weighing Accuracy

     Weighing errors occur for a number of reasons. Mistakes often result when poorly trained staff members do not fully understand how to use a scale correctly. The owner’s manual that comes with the scale should be used to train staff members. Additionally, the scale manufacturer may have a local representative available to inservice or train staff.

     To minimize weighing errors, patients should be weighed at the same time of day using the same scale. Patients should be in light clothing without shoes. If a patient has a prosthetic device, care should be taken to weigh the patient either with or without the device consistently and the medical record should contain a notation specifying whether the weight includes (or does not include) the prosthetic device. Casts also can increase a patient’s weight and should be noted as well. Other factors that can cause errors include heavier (or lighter) clothing on a patient and additional (or less) bedding or pillows on a bed or wheelchair. In addition, staff may forget to subtract the weight of a wheelchair or bed, resulting in dramatic weight fluctuations until the error is corrected. If a patient gets a new wheelchair, the new chair weight also could result in weighing errors. Having two scales available in a facility ensures scale availability should one be out of service but variances between the different scales may occur, even if they are the same model.

Maintaining Patient Privacy and Dignity

     Some facilities weigh patients before or after bathing when they are unclothed. Although this practice provides an accurate weight, the facility should be certain to maintain the patient’s dignity and right to privacy during the weighing process. Regardless of a facility’s weighing procedures, weight measurements should be obtained privately and out of view of other patients and caregivers. A patient’s weight should be considered part of the confidential medical record and falls under HIPAA guidelines for patient confidentiality.

Practice Points

     • Patient-stated weights are notoriously inaccurate and should be avoided.
     • RDs cannot complete their nutrition assessment without a weight measurement to use in calculating nutrient needs.
     • Rapid, significant weight loss and slow, insidious weight loss may impede wound healing.
     • Staff must be trained in proper use of the scale.
     • Scales must be maintained and calibrated on a regular schedule.
     • Copying weight measurements from past charts, other facilities, or even month to month for an individual patient is unethical.
     • Accurate weight measurements are essential when titrating drug dosages.

Correspondence may be sent to Dr. Collins at NCtheRD@aol.com. 

Editor’s note: Congratulations to Dr. Collins and RD411.com on receiving the 2009 Circle Award from the Dietitians in Health Care Communities. The award honors an individual or organization that has provided outstanding or unique support for Consultant Dietitians.

This article was not subject to the Ostomy Wound Management peer-review process.

1. Mahan LK, Escott-Stump S. Krause’s Food and Nutrition Therapy, 12th ed. St. Louis, MO: Saunders/Elsevier;2008;399–400.

2. Boullata J, Williams J. Cottrell F, Hudson L, Compher C. Accurate determination of energy needs in hospitalized patients. J Am Diet Assoc. 2007;107(3):393–401.

3. Determann RM, Wolthuis EK, Spronk PE, et al. Reliability of height and weight estimates in patients acutely admitted to intensive care units. Crit Care Nurs. 2007;27(5):48–55.

4. Litchford M. The Advanced Practitioner’s Guide to Wound Healing. Greensboro, NC: Case Software and Books;2006:26.