Main Blood tests for diagnosis of kidney diseases are: Serum Creatinine, Blood Urea Nitrogen (BUN), Serum Uric Acid, Electrolytes levels and Complete Urine Analysis.
Other tests to follow up Treatment of kidney disorders, after surgery, Dialysis, and Kidney Stones are listed below with interpretation of acceptable levels in blood and urine as well as the critical values which require a fast medical decision.
When to take a kidney function test?
Once You Feel or Notice Such Signs and Symptoms you should do some tests before you are going to a doctor. Symptoms may include:
weight loss and poor appetite
swollen ankles, feet or hands (due to water retention)
shortness of breath
an increased need to urinate, particularly at night
Cloudy Urine (blood or protein in your urine, protein in your urine may be not noticed as it can only be detected during a urine test)
high blood pressure (hypertension)
erectile dysfunction in men (an inability to get or maintain an erection)
General Screening tests for kidney function
General kidney function checkup tests include:
1- Serum Creatinine level
Adult: Male: 0.6–1.2 mg/dL; SI units: 53–106 mol/L. Female: 0.5–1.1 mg/dL; SI units: 44–97 mol/L
Child: 0.3–0.7 mg/dL
■ Creatinine is the breakdown product of creatine phosphate in muscle.
■ Produced at a constant rate by the body and excreted by the kidney. Blood level rises in renal impairment.
■ Serum Creatinine is the common test for renal function and Creatinine level is a sensitive indicator of renal function but is dependent on kidney function and muscle mass. Patients with decreased muscle mass do not exhibit a rise in creatinine levels as readily as those with more muscle mass and should have an estimated glomerular filtration rate (GFR) reported as well.
2- Urinalysis (UA)
Random urine sample.
■ Urinalysis provides information about the renal/urinary system.
■ Protein content in urine is indicative of decreased renal function.
■ Specific gravity measures the concentration of particles in the urine and is an indicator of the kidney’s ability to concentrate urine. It also reflects overall hydration status. Low specific gravity indicates that the urine is dilute; high specific gravity means that the urine is concentrated (volume depletion).
■ Leukocyte esterase, nitrite, and white blood cells in the urine are an indication of urinary tract infection.
■ Red blood cells indicate of damage to the renal tubules.
■ Crystals indicate the presence of renal stones like Crystals of Uric acid and Calcium Oxalate.
■ Casts are clumps of cells formed in the tubules. Hyaline casts indicate protein in the urine. WBC and RBC casts are generally indicative of upper urinary tract infection. RBC casts are also present in other serious kidney disorders. Renal tubular epithelial cell casts reflect damage to the tubules and are found in renal tubular necrosis, viral disease, and transplant rejection.
Early indicators of Kidney diseases and renal function abnormalities:
Microalbumin (MA, Urine Albumin, Albumin to Creatinine Ratio)
Normal values of Microalbumin: 0–30 mg/day
Albumin to creatinine ratio: 0 – 30 g albumin/mg creatinine; SI units: 2.5 mg albumin/mmol creatinine
Testing Sample is 24-hr or timed urine specimen.
■ This test measures minute amounts of albumin in the urine and is an early indicator of kidney damage, detecting kidney damage up to 5 years earlier than routine urine protein tests.
■ Is used to identify diabetics at risk for nephropathy so that appropriate intervention (ACE inhibitors to control hypertension and tight glycemic control).
■ Levels more than 300 mg/day (SI units: more than 300 mg/L) indicate irreversible nephropathy.
■ The timed test (4-hr or overnight urine sample) is less accurate than the 24-hr urine study. It uses a microalbumin to creatinine ratio to correct for variations in urine dilution.
Blood test for kidney abilities to filter and concentrate:
Also they are tests assess in Body Hydration Status and dehydration.
1- Electrolytes Levels in Serum and Urine
Sodium, Chloride, Potassium, Calcium, Phosphorus, and Magnesium
Sodium normal levels are 30–280 mmol/day
Required sample: 24-hour urine collection
■ Provides information about hydration status, the kidneys’ ability to conserve or excrete sodium.
2- Blood Urea Nitrogen (BUN)
Adult: 10–20 mg/dL; SI units: 3.6–7.1 mmol/L
Child: 4–16 mg/dL; SI units: 1.4–5.7 mmol/L
More than 40 mg/dL (not dehydrated/no history of renal disease)
Greater than 100 mg/dL (patient with history of renal disease)
More than 20 mg/dL increase in 24 hr (indicates acute renal failure)
■ BUN, a by-product of protein metabolism, is excreted primarily by the kidneys and therefore reflects kidney function.
■ Elevated BUN (azotemia) occurs in most renal diseases; also rises with GI bleeding, dehydration, high protein diet, and CHF.
3- Serum Osmolality Test
Normal range: 278–298 mOsm/kg H2O; SI units: 279–298 mmol/kg
Critical Levels: 265 or 320 mOsm/kg H2O
Must Sent to lab on ice.
■ Measures the concentration of particles in solution and therefore indicates hydration status.
■ Osmolality increases with dehydration and decreases with fluid overload.
4- Urine Osmolality Test
In 24-hr urine: 300–900 mOsm/kg
In Random sample: 50–1200 mOsmol/kg water
Random, timed or 24-hr urine collection. Refrigerate specimen during collection.
■ Osmolality is a measure of the number of particles in solution.
■ Used to assess electrolyte and fluid balance, the kidneys’ ability to concentrate urine, renal disease, diabetes insipidus (DI), and syndrome of inappropriate antidiuretic hormone secretion (SIADH).
■ Determination of both urine and serum osmolality aids in interpretation of results.
5- Creatinine in Urine
1–2 g/24 hr; SI units: 8.8–17.7 mmol/day
Require a 24-hr urine sample collection. Refrigerate.
■ Creatinine is a by-product of muscle breakdown. It is filtered (removed from plasma) by the kidneys and excreted in the urine.
■ Elevated levels of creatinine indicate impaired renal function.
Adult: 0.5–1 mg/L, Child: 0–3 mo: 0.8–2.3 mg/L; 4–11 mo: 0.7–1.5 mg/L; 1–17 yr: 0.5–1.3 mg/L
■ A cysteine protease inhibitor that is freely filtered (removed) by the glomeruli and thus can be used to assess for changes in glomerular filtration rate.
■ High levels of cystatin C suggest impaired renal function.
■ It is thought to be superior to creatinine as a marker of glomerular filtration rate because it is not affected by muscle mass, diet, or acute inflammatory processes.
6- Test for Protein in Urine
Normal range: 30–140 mg/24 hr; SI units: 0.01–0.14 g/24 hr
Testing a random or 24-hr urine collection. Must refrigerate during collection.
■ Urine normally contains only scant quantities of urine protein.
■ Used to assess renal function, preeclampsia, multiple myeloma.
Blood tests indicate dialysis is required:
Male: 107–139 mL/min; SI units: 1.78–2.32 mL/s. Female: 85–105 mL/min; SI units: 1.45–1.78 mL/s.
The test requires a timed urine sample (12 or 24 hr) with a blood sample taken the morning of or sometime during the test.
■ Creatinine clearance refers to the amount of blood that can be cleared of creatinine in 1 min.
■ It is calculated using the volume of urine, the amount of creatinine excreted, and the amount of creatinine in the blood.
■ It is used to determine safe dosing of nephrotoxic drugs.
Creatinine clearance of 10–20 mL/min is indicative of renal failure and the need for dialysis.
Idicator tests for Renal Diseases Complications:
1- Erythropoietin (EPO) level
Normal Range: 5–35 IU/L
■ Hormone produced by the kidney to stimulate RBC production.
■ Decreased in patients with renal disease, primary polycythemia, or after kidney surgeries.
■ Also EPO Low levels cause an Anemia due to Chronic disease.
2- Vitamin B12 in serim
160–900 pg/mL; SI units: 118–690 pmol/L
B12 deficiency can result from malabsorption from liver and kidney diseases.
3- Serum Calcium Total level
Adult: 8.2 to 10.5 mg/dL; SI units: 2.05–2.54 mmol/L
Child: 8.6–11.2 mg/dL; SI units: 2.15–2.79 mmol/L
Critical levels: 12 mg/dL; SI units: 2.99 mmol/L (coma, death).
7mg/dL; SI units: 1.75 mmol/L (tetany, death)
■ Assess for diseases of the parathyroid gland or kidneys.
Blood Test For Kidney Stones:
In addition to urine test and calculus analysis.
1- Uric Acid level in Urine
Low purine diet: 250–500 mg/day; Unrestricted diet: 250–750 mg/day
Required a 24-hr urine. Refrigerate during collection.
■ Assess for elevated levels of urine uric acid in patients with renal calculus formation or identify patients at risk for stone formation.
■ Uric acid kidney stones occur in gout or secondary to malignant diseases, ulcerative colitis, Crohn’s disease, and surgical jejunoileal bypass.
2- Cystine in Urine
Reference Ranges are 10–100 mg/24 hr
By testing a 24-hr urine collection.
■ Used to detect cystinuria or identify cause of kidney stones.
Finally, I recommend you to read about kidney roles in the body rhythms to fully understand why these tests are required, recently I posted this topic to explain the meaning of creatinine and Urea results, and How to read kidney function test results?
I have to mention that the kidney filtrate or bypass all nutrients and constituents which circulate in the blood stream, hence; Any Abnormality in the blood levels of Nutrients and their Products considered as indicator of possible renal function disturbance.
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