Contact

Daria Pašalić
Editor-in-Chief
Department of Medical Chemistry, Biochemistry and Clinical Chemistry
Zagreb University School of Medicine
Šalata ul 2.
10 000 Zagreb, Croatia
Phone +385 (1) 4590 205; +385 (1) 4566 940
E-mail: dariapasalic [at] gmail [dot] com

Useful links

S4-1

Diagnostic pathways for exclusion and diagnosis of kidney diseases. The role of urine sediment and urine protein differentiation

Walter G. Guder. Diagnostic pathways for exclusion and diagnosis of kidney diseases. The role of urine sediment and urine protein differentiation. Biochemia Medica 2015;25(Suppl 1):S26-S27.

Working Group Diagnostic Pathways of the German United Society for Clinical Chemistry and Laboratory Medicine and the Society of Nephrology, Munich, Germany

The number of patients with dialysis increases worldwide. Experts anticipate a doubling of dialysis patients in the next ten years. Therefore programs are needed to detect kidney insufficiency earlier to reduce the number of patients with end stage renal disease. Diagnostic pathways are such tools to improve diagnostic standards not only in university hospitals but in all medical institutions. Based on existing recommendations an expert group of nephrologists and clinical chemists have developed such diagnostic pathways and are presently working on relevant guidelines.

Laboratory screening for the exclusion of kidney diseases will include a sensitive marker for glomerular filtration rate in plasma/serum (cystatin C and/or reference method based creatinine) and teststrips for protein (albumin), blood, hemoglobin, myoglobin (peroxidase like activity), leucocytes (granulocyte indoxylesterase) and nitrite, based on either specific gravity (conductivity) or creatinine. In addition a visual examination of urine seems still useful to confirm observations of patients (colour, turbidity). Urine sediment is indicated only in this early stage, when one of the following symptoms or signs is present: Suspicion of cystinuria and other pathogenetic stone forming crystals, clarification of positive test strip fields for blood, leucocytes or nitrite.

In hematuria and/or leucocyturia urinary sediment can help to differentiate prerenal from renal and postrenal causes by identifying erythrocytes, erythrocyte casts and quantitate acanthocytes. When the latter increase above 10% of erythrocytes or erythrocyte casts are seen, a renal cause of hematuria is to be assumed. On the other hand, inclusion of α2-macroglobulin/albumin ratio can clearly separate renal from postrenal causes. Leucocyte casts indicate a renal cause of leucocyturia. Here α1-microglobulin/creatinine ratio > 14 mg/g indicates a renal cause of leucocyturia (like pyelonephritis, but also secondary tubular insufficiency due to high pressure in the postrenal pathways caused by stones or prostate adenoma). In proteinuria (albumin > 20 mg/g creatinine) prerenal, glomerular and postrenal causes can be differentiated by stepwise measurement of the respective proteins.

After urine proteins can be measured on routine analysers in a stepwise manner, and sediment constituents can be measured by flow cytometric and microscopic analyzers, both strategies may be used in an experienced laboratory to provide the clinician with interpretative results answering the medical question regarding kidney diseases. After the protein differentiation technique seems of the same diagnostic sensitivity and specificity as other new markers of tubular insufficiency, urine sediment analysis may sustain its importance in experienced hands (eyes) in well-defined areas of differential diagnosis in urology and nephrology.

e-mail: walter [dot] guder [at] extern [dot] lrz-muenchen [dot] de

S4-2

Estimated glomerular filtration rate – from theory to practice

Vanja Radišić Biljak.Estimated glomerular filtration rate – from theory to practice. Biochemia Medica 2015;25(Suppl 1):S27-S29.

Department of Medical Biochemistry and Laboratory Medicine, Merkur University Hospital, Zagreb, Croatia

 

Chronic kidney disease (CKD) is a world-wide public health problem, with adverse outcomes of kidney failure, cardiovascular disease, and premature death. CKD typically evolves over many years, with a long latent period when the disease is clinically silent and therefore diagnosis, evaluation and treatment is based mainly on biomarkers that assess kidney function.

Glomerular filtration rate (GFR) remains an ideal marker of kidney function. However, the gold standard for measuring GFR has been a plant polysaccharide called inulin, an exogenous substance requiring injection and a complex collection protocol. Alternatives involve administration of radionuclides such as 125I-iothalamate, 51Cr-EDTA or 99mTc-DTPA. All these procedures are labour-intensive and too costly for routine use. None of these techniques is suitable as a screening procedure for the detection of CKD.

As one of the possible alternatives, a 24 h urine creatinine clearance has been regarded as a more sensitive tool for the detection of kidney failure. However, the inconvenience of a timed urine collection, failure to collect the entire specimen, and the wide within-subject variability, restrict the usefulness of this procedure. Furthermore, there is some tubular secretion of creatinine and as a result, healthy individuals could have a creatinine clearance 10 do 40% higher than measured by inulin clearance, thereby overestimating GFR and masking any future or present renal impairment.

The National Kidney Foundation, through its Kidney Disease Outcomes Quality Initiative (K-DOQI) recommended use of estimates of GFR calculated from prediction equations based on plasma or serum creatinine and general demographic data (age, sex, gender). GFR estimating equations are useful because they provide a more accurate estimate of measured GFR than the serum level of the filtration marker alone (creatinine, cystatin C); they are expressed in the same units as measured GFR, which facilitates clinical decisions based on the level of kidney function. Large number of laboratories throughout the world routinely report eGFR with every creatinine request (UK, France, Australia, more than 80% of US clinical laboratories). And there is a change from mostly used MDRD (Modification of Diet in Renal Disease study) equation for GFR estimation to CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, which uses the same variables as the MDRD study but is more accurate across the range of GFR. Also, CKD-EPI is the recommended equation for routine eGFR reporting by the KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease.

Recently conducted survey among Croatian medical-biochemistry laboratories showed that laboratory diagnostics of CKD is not standardized. Almost 74% of laboratories do not report eGFR. The most commonly used equation for GFR estimation is MDRD equation. What is very concerning is the observed discrepancy between routine method for serum creatinine measurement and equation used for eGFR calculation seen in some laboratories. For that reasons joint Working group (WG) of Croatian society of medical biochemistry and laboratory medicine and Croatian chamber of medical biochemists was established in 2014. with the very first goal to produce easily applicable national recommendations for laboratory diagnostics of CKD.

e-mail: vanja [dot] radisic [at] gmail [dot] com

S4-3

Acute renal failure

Lorena Honović. Acute renal failure. Biochemia Medica 2015;25(Suppl 1):S29-S31.

Department of Laboratory Diagnostics, General Hospital Pula, Pula, Croatia

Acute renal failure (ARF) is a clinical syndrome characterized by a rapid and sudden reduction of blood flow through the kidneys and significant reduction in glomerular filtration (GF), which takes place in a very short period of time. Reduction of GF causes reduced urine excretion, disturbance of electrolyte (hyperkalemia, hyperphosphatemia, hypocalcemia), disturbance of acid-base balance (acidosis) and accumulation of nitrogen compounds (azotemia). Urea formation and blood clotting is disturbed. The excretion of urine is affected, and depending on the type and cause of ARF, almost 3/4 of cases show oliguria or anuria. The clinical ARF reflects the primary illness or surgical procedure that is initiated. The accumulation of fluid in the lungs causes shortness of breath and crepitus. Depending on the defect (glomerulonephritis or myoglobinuria) urine can be dark brown, and obstruction of expulsion tract may be palpated as stretch bladder.

The causes of ARF are most commonly hemodynamic disorders, infections, metabolic disorders, physical and chemical agents, and damage may occur at the vascular system kidney glomeruli and tubules. Clinical syndromes can be divided into three basic groups: prerenal, renal (intrinsic) and postrenal.

Any condition with marked hypovolemia, reduction of the effective volume of circulating blood due to systemic vasodilation, or the reduced stroke volume of the heart, can lead to the development of prerenal ARF. Kidney parenchyma cells are not damaged, and the correction of hemodynamic disorders normalizes renal function. Hypoperfusion causes increased reabsorption of sodium and water with oliguria and high urine osmolality with low sodium in urine.

Renal ARF most often occurs due to primary renal disease or renal injury leading to prolonged ischemia, tubular and interstitial disease, kidney disease or glomerular microcirculatory disease. In addition to these, the reasons may be nephrotoxicity of some drugs and intravenous iodine contrast agents. Damage to the tubules reduces the reabsorption of sodium and the concentration of sodium in the urine increased, which helps in the diagnosis.

Obstruction of urine leakage can lead to postrenal ARF, and it can occur in patients with bilateral obstruction, obstruction below the bladder, or in the case of unilateral obstruction of the only functioning kidney. Because of the obstruction of the flow, the GF decreased, the flow through the kidneys is disrupted and after 24 hours GF decreased <50% of normal due to the increased resistance in the renal vascular system.

There are two proposed criteria for diagnosis and staging of ARF: AKIN (Acute Kidney Injury Network) and the RIFLE (Risk, Injury, Failure, Loss, and End-Stage Kidney Disease). According to RIFLE criteria, ARF is classified into five stages based on the percentage increase in serum creatinine or decrease in GF. An AKIN criterion classifies ARF in three stages using the absolute value of the increase in serum creatinine.

Diagnosis of ARF requires a complete assessment by a clinician: reviewing the history of the disease because of possible nephrotoxic influence, monitoring urine volume, searching for systemic diseases that might affect kidney function, imaging techniques (ultrasound, CT, MRI) to assess the size of the kidney. If the diagnosis is unclear kidney biopsy should be performed.

Laboratory diagnostics of ARF traditionally includes the determination of serum creatinine (and estimation of GF), potassium, urea, inorganic phosphate, ABS, examination of urine sediment and lately determination of the newer markers of kidney damage, such as NGAL (Neutrophil Gelatinase-Associated Lipocalin) and KIM-1 (Kidney Injury Molecule).

ARF is most common in hospitalized patients with injuries, burns, extensive bleeding or those undergoing major surgery in which it can be prevented by maintaining fluid balance, blood volume and blood pressure. Given that AFR is associated with significant morbidity and mortality, it requires a systematic approach for prevention, early detection and diagnosis.

 

e-mail: lhonovic1 [at] gmail [dot] com