Chronic Kidney Insufficiency: Test and Diagnosis

1st-order laboratory parameters-obligatory laboratory tests.

  • Small blood count
  • Inflammatory parameters – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate).
  • Electrolytes (blood salts)
    • Calcium ↓
    • Sodium ↓
    • Potassium ↑ (initially normal potassium concentration despite impaired renal function due to compensatory increase in renal and intestinal potassium secretion; later hyperkalemia due to metabolic acidosis triggering potassium leakage from cells, and possibly due to excessive alimentary (“dietary”) potassium intake).
    • Magnesium ↑ (during compensated renal failure, serum magnesium concentrations are usually within the normal range, but may be decreased)
    • Phosphate ↑
  • Fasting glucose (fasting blood glucose).
  • Urine status (rapid test for: pH, leukocytes, nitrite, protein, glucose, ketone, blood), sediment, urine culture (pathogen detection and resistogram, that is, testing of suitable antibiotics for sensitivity/resistance)[sediment: erythrocyte and leukocyte cylinders always have a pathological value].
  • Renal parameters – urea, creatinine, cystatin C if necessary [Note: creatinine is unsuitable as an early marker of renal disease].
  • Creatinine clearance – quotient of urine creatinine multiplied by urine volume in 24 h divided by blood serum creatinine multiplied by time; calculated, gives the amount of creatinine excreted into the urine per minute; the “creatinine clearance” gives the GFR (glomerular filtration rate), according to which chronic renal failure is classified into stages (see Introduction)Determination of the GFR (glomerular filtration rate) according to the formula of the MDRD* study (Modification of Diet Renal Disease) from the serum parameters creatinine, urea and albumin – taking into account age, sex and indication of black skin color – according to the European Guidelines). Caution. In normal subjects, the MDRD formula* determines the GFR too low; in chronic kidney disease (cN), the result is acceptable in terms of compliance.
  • Urine examination from 24-hour collected urine: total protein, albumin; quantitative determination of proteinuria (e.g., as albumin-creatinine ratio in spontaneous or collected urine; if necessary, together with the determination of creatinine clearance).
  • Practical online calculator
    • https://www.kidney.org/professionals/kdoqi/gfr_calculator and
    • for SI units: https://www.niddk.nih.gov/health-information/communication-programs/nkdep/laboratory-evaluation/glomerular-filtration-rate-calculators/ckd-epi-adults-si-units.
    • Kidney Failure Risk Equation (KFRE): to determine the risk of needing dialysis within 2 or 5 years: Online calculator

Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.

  • Protein electrophoresis in urine – method for proteinuria differentiation (protein excretion in urine).
  • Erythropoietin (synonyms: erythropoietin, EPO) – ↓ in renal anemia (due to diurnal fluctuations blood collection in the morning: 08.00 am – 10.00 am).
    • EPO is further decreased in:
      • AIDS
      • Tumor anemia
      • Polycythaemia vera
  • 1,25-Dihydroxy vitamin D (synonym: 1,25-OH-D3, calcitriol) – decreased in renal insufficiency, nephrotic syndrome.
  • Parathyroid hormone [renal insufficiency: PTH ↑ (hyperparathyroidism/parathyroid hyperfunction), Ca2+ ↓]
  • Uric acid ↑; Note: uric acid is 70-80% excreted by the kidneys (urinary).

Monitoring of patients with renal disease not requiring dialysis [guideline: DEGAM]

  • Monitoring intervals should be agreed upon individually depending on CKD stage, proteinuria, diabetes mellitus, or hypertension.
  • Albumin-creatinine ratio or microalbuminuria only needs to be routinely checked in diabetes mellitus.
  • Serum hemoglobin should be checked once a year in patients without known anemia from stage G3b (GFR 30-44) and semiannually from stage G4 (GFR 15-29) to G5 (GFR < 15).
  • If the hemoglobin level is below 11 mg/dl, the iron status (serum ferritin level and serum transferrin saturation) should be checked.
  • Calcium, phosphate, parathyroid hormone, and vitamin D should be measured once starting at a CKD stage ≥ G4 and then monitored individually.

Further notes

  • * The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) has redeveloped the MDRD formula, which includes the same four parameters but weights them differently. The CKD-EPI formula results in a decrease in the prevalence of renal failure (stage 3 to 5) from 8.7% to 6.3%.
  • The GFR calculated from the combination of cystatin C and creatinine is closer to the true GFR than that calculated from the individual parameters. It can be used to confirm chronic kidney disease.
  • Patients with chronic kidney disease and a GFR < 45 ml/min/1.73 m2 (CKD stage 3b or higher) should have serum calcium, phosphate, iPTH, and 25-OH vitamin D3 determined.