In practice, the best source of information will be your patient. It is best to assess the patient for any reported and/or observable change. During assessment, the patient may not be able to quantify values so our responsibility is to provide estimate options instead. Also, the symptoms enumerated are also affected by contextual issues and conditions present in the patient. For example, oliguria, may be a baseline condition already in the patient based on history. You may measure the amount through I&O for a specific time and compare it with reference values based on books OR you may measure the same amount and compare it with a baseline value based on the patient’s data. In this case, which basis for comparison will be more important in assessing the patient’s condition: the reference values based on books or the trend in the patient? The answer would be the change in the trend in the patient compared to their baseline.
That’s why I didn’t provide specific values. We always, ideally, use the patient’s baseline information as the more important basis of comparison for change in patterns.
Different references documents will have different reference values, anyway. Even individual institutions will vary in their normal ranges depending on their reference studies. Most institution will provide the reference values.
However, the reference ranges don't usually vary that much among institutions and/or references. Having said that, I still use Brunner and Suddarth’s (B&S Med-Surg Nursing MSN). Our task is to facilitate to highlight important concepts based on the topic, but you still need to read the books and reputable references, especially if they are not clear in the lectures.
1. How "frequent" is frequent urination?
According to B&S MSN, frequent urination is more than every 3 hours. However, this is very much affected by fluid intake. So frequency shouldn’t be assessed just as the frequency but also should take account the context of any patterns or conditions.
2. What is the amount of urine to say that it is anuria? Oliguria? Polyuria?
B&S MSN: Anuria is UO <50 ml/day. But do you really need to wait for 24 hours to measure <50 ml to say anuria is present if a patient who just voided once every three hours the previous day?
B&S MSN: Oliguria is UO <0.5ml/kg/hr. In the outpatient or public health setting, in patients with chronic conditions (which is the case in most patients), can we realistically expect patients to actually measure their UO qh or q shift? During initial assessment and nursing history, can we realistically expect the patient to provide us information/estimates on urine output in ml/hour? In acute settings/conditions especially in the hospital, yes, it is important especially if anticipating and monitoring for fluid congestion and its effects.
B&S MSN: Polyuria is increased volume in the urine. Harrison’s Principles of Internal Medicine (HPIM) says UO >3L /24 hour. But, again, this is very context-specific. Increase in fluid volume in the context of increased fluid intake will not tell you much about kidney function. It would make sense for someone who drank 10-12 glasses of water to increase in their urine output. The better reference would be comparing urine output with fluid intake first before determining if there is polyuria.
3. What are the normal values of BUN, serum creatinine, GFR, urine specific gravity?
- Urine Specific Gravity: 1.010-10.025
- Osmolality: Serum 280-300 mOsm/kg, Urine 200-800mOsm/kg/24 hr
- Creatinine level 0.6-1.2mg/dl But this doesn’t say much if you don’t use it to estimate GFR
- eGFR varies according to age and sex.
- BUN: 7-18mg/dl; patients >60 years 8-20 mg/dl
HPIM: “A significantly reduced GFR (either acute or chronic) is usually reflected in a rise in PCr, leading to retention of nitrogenous waste products (defined as azotemia) such as urea. Precise determination of GFR is problematic, as both commonly measured indices (urea and creatinine) have characteristics that affect their accuracy as markers of clearance. Urea clearance may underestimate GFR significantly because of urea reabsorption by the tubule. In contrast, creatinine is derived from muscle metabolism of creatine, and its generation varies little from day to day.”
The main point is, and one thing we were taught in healthcare, we assess the patients based on their signs and symptoms. We only use the lab results to validate our hypotheses on what’s happening to the patient as manifested by signs and symptoms. I didn’t indicate the actual lab values because, more than different references indicating different values, I expect you to learn more about the symptoms associated with the conditions and how they develop so that you understand the reason for the medical and nursing management therapies for the condition. I didn’t place them there because I want you to understand the relationship between pathophysiologic processes, the manifestations, and the rationale for the management; not to memorize normal values because those are something that should have been emphasized in physiology and pathophysiology.
I hope the answers were adequate. But, more than, that, I hope the explanation clarifies what is the focus of the interventions courses.😊
- Dr. JCVAlejo