Abnormal kidney function As kidney function decreases, the kidneys are less able to main- tain appropriate fluid concentrations in the body. Salts and fluids become increasingly difficult to remove from the bloodstream as the glomerular filtration rate (GFR) decreases, resulting in edema and hypertension. Edema, or fluid overload, can cause symptoms such as swollen ankles and legs, as well as shortness of breath due to an accumulation of fluid in the lungs, known as pulmonary edema (DiPiro et al., 2019). A decline in kidney function can also result in a decreased ability to remove metabolic byproducts, such as phosphorus and creat- inine. High phosphorus levels can lead to decreased blood calci- um levels, which triggers the parathyroid glands to release more parathyroid hormones to stimulate the release of calcium from the bones into the bloodstream. If this mechanism is not suppressed, it can lead to an excessive release of calcium from the bones, resulting in bone demineralization, weaker bones, and bone pain. Since the kidneys activate vitamin D, lower levels of calcitriol can be seen in patients with kidney disease, exacerbating bone condi- tions. Blood creatinine levels predictably increase in patients with decreased kidney function. The increase in creatinine level is used to determine the level of kidney dysfunction, as it is a component in the calculation of glomerular filtration rate (DiPiro et al., 2019). Decreased kidney function also can cause a decrease in eryth- ropoietin production, which is typically seen in later stages of disease progression. This causes a decrease in red blood cell production, which leaves fewer red blood cells to carry oxygen through the bloodstream to the tissues. The resulting effect is anemia, which can cause patients to become tired more easily, feel weak, get dizzy easily, and develop shortness of breath after
minimal activity. Chronic kidney disease patients with severe ane- mia may require administration of synthetic erythropoietin if the kidneys are unable to maintain production (DiPiro et al., 2019). As kidney function declines, patients may be required to make diet modifications to prevent accumulation of unwanted sub - stances. Renal diets typically involve decreasing potassium, sodi- um, and phosphorus intake to prevent overaccumulation of these substances. Fluid restriction may also be required depending on the level of kidney disease. Medications to bind phosphates and supplement vitamin D levels may be required, depending on the severity of accumulation (DiPiro et al., 2019). Symptoms may emerge when waste products begin to accumu- late, causing a syndrome called uremia . Uremia typically occurs as a result of end-stage kidney disease, when the kidneys are unable to filter toxins through the urine. Patients with uremia can experi - ence headaches, fatigue, nausea, vomiting, decreased appetite, decreased ability to concentrate, and an increased tendency to bleed. High phosphorus levels may also cause itching. Treatment typically involves dialysis or kidney transplantation (DiPiro et al., 2019). Self-Assessment Quiz Question #1 Renal diets can involve decreasing the intake of all of the follow- ing to prevent over accumulation EXCEPT: a. Potassium. b. Sodium. c. Phosphorus. d. Calcium.
CALCULATING KIDNEY FUNCTION
Overall kidney function is estimated by calculating the glomeru- lar filtration rate (GFR). This rate describes the flow rate of fluid filtered by all glomeruli, presented as milliliters per minute, and can be calculated in several different ways. The National Kidney Foundation recommends using the CKD-EPI creatinine equation to estimate GFR. This equation takes age, sex, and serum cre- atinine level into account to calculate an estimated glomerular filtration rate. The calculation is as follows (National Kidney Foun - dation, 2021): GFR = 142 × min (S cr /k, 1) a × max(S cr /k, 1) –1.200 × 0.9938 age × 1.012 [if female] ● S cr = serum creatinine in mg/dL ● k = 0.7 for females and 0.9 for males
There are many online calculators available to estimate GFR using this equation, such as the one provided by the National Kidney Foundation, found at https://www.kidney.org/professionals/kdo- qi/gfr_calculator Healthcare Consideration: In the past, many health care profes- sionals were trained to calculate creatinine clearance using the Cockcroft–Gault equation to estimate kidney function. Creatinine clearance calculations using this equation tend to exceed true GFR by between 10% and 20% or more, depending on the pro- portion of urinary creatinine derived from tubular secretion. In the past, this error was balanced by a nearly equivalent error in mea- suring serum creatinine, but national standardization of blood creatinine assays has essentially removed this error. Therefore, creatinine clearance measurements using the Cockcroft–Gault equation typically reflect a GFR that is falsely inflated, which should be considered when calculating medication dosages for patients with kidney disease (Inker & Perrone, 2021). ● Stage 5 : Kidney failure (GFR <15 mL/min/1.73 m 2 or dialysis). In stages 1 and 2, the GFR alone should not be used to diagnose chronic kidney disease because GFR greater than 60 mL/min/1.73 m 2 may be considered borderline normal. In these cases, the pres- ence of one or more markers of kidney damage should be used to determine the diagnosis (KDIGO Work Group, 2013): ● Albuminuria (albumin excretion >30 mg/24 hr or albumin:cre- atinine ratio >30 mg/g). ● Urine sediment abnormalities. ● Electrolyte and other abnormalities related to tubular disor- ders. ● Histology abnormalities. ● Structural abnormalities of the kidney, often detected using imaging studies. ● History of kidney transplantation.
● a = –0.241 for females and –0.302 for males ● Min indicates the minimum of S cr /k or 1 ● Max indicates the maximum of S cr /k or 1
DEFINING CHRONIC KIDNEY DISEASE
The Kidney Disease: Improving Global Outcomes (KDIGO) Work Group defines chronic kidney disease as abnormalities of kidney structure or function, present for greater than three months, with implications for health. This can be measured by a glomerular fil - tration rate (GFR) of less than 60 mL/min/1.73m 2 , or it can be de- fined by one or more markers of kidney damage (kidney disease: Improving Global Outcomes [KDIGO] Work Group, 2013a). Chronic kidney disease is classified into five stages, with stage 1 indicating the mildest form of disease and stage 5 representing kidney failure (KDIGO Work Group, 2013): ● Stage 1 : Markers of kidney damage found, but GFR is normal or increased (>90 mL/min/1.73 m 2 ). ● Stage 2 : Mildly reduced GFR (60–89 mL/min/1.73 m 2 ). ● Stage 3a : Mildly to moderately reduced GFR (45–59 mL/ min/1.73 m 2 ). ● Stage 3b : Moderately to severely reduced GFR (30–44 mL/ min/1.73 m 2 ). ● Stage 4 : Severely reduced GFR (15–29 mL/min/1.73 m 2 ).
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