NPNs and Kidney Function Flashcards

Vocabulary-style flashcards covering Non-Protein Nitrogen (NPN) compounds (BUN, Uric Acid, Creatinine, Ammonia), their clinical significance, analytical methods, and basic renal function testing as described in the lecture notes.

Non-Protein Nitrogen (NPN) Compounds

Waste products traditionally used to monitor renal function, including urea, uric acid, creatinine, and ammonia.

Urea (Blood Urea Nitrogen)

The major excretory product of protein metabolism, primarily produced in the liver from amino groups and ammonia; it is the NPN of highest concentration in the blood.

Coupled Enzymatic Method (Urea)

The most common analytical method for urea which starts with the conversion of urea to ammonium ion by the enzyme urease.

Glutamate Dehydrogenase Method

The most specific urea measurement method where ammonium ion is reacted with oxoglutarate and NADH; measurement is based on the disappearance of NADH at $340\,\text{nm}$.

Diacetylmonoxime Method

A chemical method for urea based on the Fearon Reaction where urea is coupled with diacetyl to produce diazine, measured at $540\,\text{nm}$.

Isotope Dilution Mass Spectrophotometry (IDMS)

The reference method for all NPNs, involving the detection of characteristic fragments following ionization and quantification using isotope-labelled compounds.

Azotemia

The laboratory description for elevated concentrations of non-protein nitrogens (NPNs) in the body.

Uremia

A condition characterized by elevated concentrations of NPNs accompanied by clinical signs and symptoms such as bronze-colored skin, anemia, and distended abdomen.

Prerenal Azotemia

Azotemia caused by conditions leading to reduced blood flow to the kidneys (e.g., congestive heart failure) or increased protein metabolism.

Renal Azotemia

Azotemia caused by intrinsic kidney problems, such as damage from UTIs or abnormally small kidneys, often leading to anemia due to decreased erythropoietin.

Post-Renal Azotemia

Azotemia caused by the obstruction of urine flow anywhere in the urinary tract, such as renal stones or kinked ureters.

BUN to Urea Conversion

The calculation used to find urea concentration by multiplying the Urea Nitrogen value by $2.14$.

Blood Uric Acid (BUA)

The product of purine catabolism (adenosine and guanine) in the liver; $70\%$ is excreted by the kidneys while the rest is excreted via the GI tract.

Monosodium urate

The dominant form of uric acid in the plasma at a pH of $7$, which can crystallize in joints at concentrations greater than $6.8\,\text{mg/dl}$.

Caraway Method

A chemical method for uric acid where uric acid is oxidized to allantoin while Phosphotungstic acid (PTA) is reduced to tungsten blue in an alkali solution.

Uricase Method

The first step in enzymatic uric acid analysis where uric acid is reacted with oxygen and water to produce allantoin, $\text{CO}_2$, and hydrogen peroxide.

Lesch-Nyhan Syndrome

An X-linked disorder (seen in males) caused by a complete deficiency of Hypoxanthine Guanine Phosphoribosyltransferase (HGPRT), leading to an inability to recycle purine bases and resulting in hyperuricemia.

Tophi

Microscopically identifiable deposits of crystalline uric acids and urates in tissues.

Creatinine

A waste product derived from muscle creatine and creatine phosphate that is excreted at a constant rate and is inversely related to the glomerular filtration rate.

Jaffe Reaction

A method where creatinine reacts with picric acid in an alkali solution to produce a red-orange chromogen; it is subject to interference from glucose and pyruvate.

Kinetic Jaffe Method

A high sensitivity and specificity method where serum is mixed with alkaline picrate and the rate of change in absorbance is measured.

Ammonia

A toxic byproduct of amino acid deamination that is normally converted to urea in the liver; elevated levels can lead to neurotoxicity and Hepatic Encephalopathy.

Conway Method

An analytical method for ammonia where ammonia gas diffuses into a separate compartment and is absorbed in a pH indicator solution for titration.

Berthelot Method

A spectrophotometric method for ammonia analysis using phenol and hypochlorite (Berthelot reagent) to produce indophenol blue.

Glomerular Filtration Rate (GFR)

The volume of plasma filtered by the glomerulus per unit of time, computed as $\text{GFR} = \frac{U_c \times V_u}{P_c \times t}$.

Clearance

Specifically defined as the volume of plasma from which a substance is removed per unit of time; Creatinine Clearance (CrCl) provides a reasonable estimate of GFR.

Renal Threshold

The plasma concentration above which a substance (such as glucose) appears in the urine; it does not exist for water.

Panel C Excretion Process

Occurs when a substance is freely filtered and fully reabsorbed (e.g., Amino Acids and Glucose), resulting in an excretion rate of $0$.